Weed Science
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Questions and Answers

What is one major consequence of weed competition on crop growth?

  • Increased nitrogen availability
  • Reduced leaf area development (correct)
  • Enhanced crop growth rate
  • Increased resistance to pests

    • Which weed type is specifically noted for being efficient in CO2 utilization?

  • C3 type weeds
  • Perennial weeds
  • C4 type weeds (correct)
  • Annual weeds

    • How does crop density influence weed competition?

  • Crop density has no effect on weed competition
  • Higher crop density decreases weed growth (correct)
  • Higher crop density increases weed growth
  • Weed growth becomes independent of crop density

    • Which factor does NOT influence the potential of allelochemicals in soil?

    <p>Presence of beneficial insects</p> Signup and view all the answers

    Which of the following is NOT a factor that affects competitive ability of crops against weeds?

    <p>Soil type</p> Signup and view all the answers

    What is the primary objective of a weed management system?

    <p>To maintain an environment that is detrimental to weeds</p> Signup and view all the answers

    What is the effect of dense weed growth on young crop seedlings?

    <p>Suppresses their growth</p> Signup and view all the answers

    Which crop is considered to be more susceptible to weed competition based on its growth characteristics?

    <p>Dwarf varieties of crops</p> Signup and view all the answers

    Which of the following plants inhibits the growth of corn?

    <p>Jatropha curcas</p> Signup and view all the answers

    What happens to crop yield when weed density increases?

    <p>Crop yield often decreases</p> Signup and view all the answers

    Which principle is NOT part of weed control methods?

    <p>Cultivation</p> Signup and view all the answers

    Under what conditions does competition for light become most significant in crop-weed interactions?

    <p>When moisture and nutrients are plentiful</p> Signup and view all the answers

    How do abiotic stress factors affect allelochemicals?

    <p>They can enhance the activity of allelochemicals.</p> Signup and view all the answers

    What is a recommended preventive measure to control weeds?

    <p>Clean farm machinery thoroughly before moving between fields</p> Signup and view all the answers

    Which plant inhibits seed germination and root growth of pigweed?

    <p>Sour Orange</p> Signup and view all the answers

    Which method contributes to the eradication of weed establishment?

    <p>Digging and burning new weed patches</p> Signup and view all the answers

    What is the main characteristic of annual weeds?

    <p>Complete their life cycle in one year</p> Signup and view all the answers

    Which of the following plants is an example of a biennial weed?

    <p>Rottboellia exaltata</p> Signup and view all the answers

    Which characteristic distinguishes sedges from grasses?

    <p>Sedges have triangular stems</p> Signup and view all the answers

    What type of weeds are obligate weeds?

    <p>Only found in cultivated areas</p> Signup and view all the answers

    Which of the following is considered a perennial weed?

    <p>Cyperus rotundus</p> Signup and view all the answers

    Which of the following describes aquatic weeds that are free floating?

    <p>Float on the water surface and are not attached to soil</p> Signup and view all the answers

    What do broadleaf weeds generally have?

    <p>Netted venation and broadleaf structure</p> Signup and view all the answers

    Which of the following best describes common weeds?

    <p>Annual, biennial, or simple perennials commonly found in farms</p> Signup and view all the answers

    What is the primary goal of eradication measures in weed control?

    <p>To completely remove a weed species from an area</p> Signup and view all the answers

    Which method is NOT classified as a weed control method?

    <p>Aerobic methods</p> Signup and view all the answers

    What are control measures primarily concerned with in weed management?

    <p>Minimizing weed growth and intensity</p> Signup and view all the answers

    Which of the following is considered a mechanical method of weed control?

    <p>Hand hoeing</p> Signup and view all the answers

    What is one of the primary characteristics of weed management?

    <p>Systematic planning to minimize weed invasion</p> Signup and view all the answers

    When is eradication most likely to be pursued in relation to weed species?

    <p>When the weed species is new and highly noxious</p> Signup and view all the answers

    Which of the following is a reason for the high cost and difficulty of eradication measures?

    <p>It is usually attempted in small areas</p> Signup and view all the answers

    What distinguishes weed control from weed management?

    <p>Weed control focuses on immediate suppression while weed management involves long-term planning</p> Signup and view all the answers

    How many liters of the commercial formulation are required for treating a 0.5-ha area with a 0.04% concentration fungicide?

    <p>0.12 liters</p> Signup and view all the answers

    What is the total volume of spray needed for a 0.5-ha area if 300 liters of spray solution are applied per hectare?

    <p>150 liters</p> Signup and view all the answers

    If the recommended rate for a pesticide is 0.75 kg ai/ha, how much is required for a 0.5-ha area?

    <p>0.53 kg</p> Signup and view all the answers

    What is the formula used to calculate the amount of commercial formulation required?

    <p>Recommended rate x area x 100 / percent a.i.</p> Signup and view all the answers

    How many kilograms of commercial formulation are needed to treat a 0.5-ha area with a recommended rate of 0.75 kg ai/ha and 70% a.i. formulation?

    <p>0.57 kg</p> Signup and view all the answers

    If applying a pesticide granule at a rate of 0.5 kg ai/ha to a 2-ha field, how much total active ingredient is required?

    <p>1.0 kg</p> Signup and view all the answers

    What is the capacity of the sprayer if 0.536 kg of commercial formulation is used for a total spray volume of 175 liters?

    <p>16 liters</p> Signup and view all the answers

    What amount of the active ingredient is delivered per sprayer load if 0.536 kg of commercial formulation is used in a 16-liter sprayer?

    <p>0.049 kg</p> Signup and view all the answers

    What is the primary goal of weed science as a discipline?

    <p>To formulate efficient and cost-effective weed control methods.</p> Signup and view all the answers

    Which of the following is considered a beneficial effect of weeds?

    <p>Weeds provide shelter to wildlife.</p> Signup and view all the answers

    How many weed species are estimated to cause serious losses worldwide?

    <p>About 18,000</p> Signup and view all the answers

    Which of the following statements best defines weeds?

    <p>Plants with no economic value.</p> Signup and view all the answers

    What role do weeds play in soil health?

    <p>They add organic matter to the soil.</p> Signup and view all the answers

    Which of the following organizations is focused on weed science in Asia?

    <p>Asian Pacific Weed Science Society (APWSS)</p> Signup and view all the answers

    What type of plant is characterized as a basophilic species?

    <p>Agrophyron repens</p> Signup and view all the answers

    What is a commonly accepted definition of weeds?

    <p>Plants growing out of place or interfering with human interest.</p> Signup and view all the answers

    What is the primary resource that weeds compete for in agro-ecosystems?

    <p>All of the above</p> Signup and view all the answers

    What effect do weeds have on crop yield?

    <p>Weeds reduce crop yield by competing for resources.</p> Signup and view all the answers

    Which practice is known to discourage the growth of nutsedge?

    <p>Repeated cultivation</p> Signup and view all the answers

    Which of the following nutrient accumulators is noted for its nitrogen accumulation?

    <p>Amaranthus viridis</p> Signup and view all the answers

    How do weeds primarily affect crop plants in agricultural systems?

    <p>Through competition and allelopathy</p> Signup and view all the answers

    What defines the relationship of competition between crops and weeds?

    <p>Crops and weeds compete for limited resources</p> Signup and view all the answers

    Which factor is NOT typically considered part of the soil factors affecting weed growth?

    <p>Crop rotation</p> Signup and view all the answers

    Which of the following is a characteristic of acidophilic plants?

    <p>They prefer a pH of about 4.5 to 6.0</p> Signup and view all the answers

    What is the primary reason why weeds may lower crop yield?

    <p>Weeds compete for nutrients, moisture, and light.</p> Signup and view all the answers

    Which factor does not typically affect crop-weed competition?

    <p>Soil temperature</p> Signup and view all the answers

    How does the type of weed species influence crop competition?

    <p>Some weed species may hinder crop growth through different mechanisms.</p> Signup and view all the answers

    Which crop characteristic typically offers an advantage against weed competition?

    <p>Fast canopy formation</p> Signup and view all the answers

    What is the effect of increased weed density on crop yield?

    <p>Decreased yield as weeds compete more intensely with crops.</p> Signup and view all the answers

    What factor can influence the competitive ability of crop plants against weeds?

    <p>The growth stage of crops.</p> Signup and view all the answers

    Why is competition for light said to be crucial during certain growth stages?

    <p>It can impact flowering and seed development.</p> Signup and view all the answers

    Which of the following typically characterizes the competitive ability of fast canopy-forming crops compared to slow growers?

    <p>Faster growth allows them to outcompete weeds effectively.</p> Signup and view all the answers

    Which factors are indicated to influence the potential of allelochemicals in soil?

    <p>Soil temperature and moisture</p> Signup and view all the answers

    What is a primary aim of implementing preventive methods in weed management?

    <p>To prevent the introduction and spread of weeds</p> Signup and view all the answers

    Which of the following is NOT a stated principle of weed control?

    <p>Irrigation</p> Signup and view all the answers

    What effect does Sour Orange have on the growth of pigweed?

    <p>Inhibits seed germination and root growth</p> Signup and view all the answers

    How does Leucaena influence the yield of various crops?

    <p>Reduces yield of wheat and turmeric but increases yield of maize and rice</p> Signup and view all the answers

    Which type of stress factors can influence the activity of allelochemicals?

    <p>Both abiotic and biotic stresses</p> Signup and view all the answers

    Which weed is known to inhibit the growth of corn?

    <p>Jatropha curcas</p> Signup and view all the answers

    What is the outcome of inadequate preventive measures in weed control programs?

    <p>Increased weed infestation</p> Signup and view all the answers

    How many loads are required to spray at a rate of 300 liters/ha in a 0.6-ha field using a 16-liter sprayer?

    <p>11.25 loads</p> Signup and view all the answers

    What is the % concentration of a spray solution if 5 tbsp of 70% WP product is mixed with 16 liters of water?

    <p>0.21%</p> Signup and view all the answers

    What formula is used to calculate the amount of sprayer loads needed?

    <p>No.of loads = desired spray volume x area of field / size of sprayer</p> Signup and view all the answers

    If a 16-liter sprayer is used and one wishes to apply a total of 320 liters over a 0.5-ha area, how many loads must be completed?

    <p>12 loads</p> Signup and view all the answers

    How many grams of active ingredient (a.i.) are required per hectare if a formulation of 20 grams of 50% WP is used per 5 gallons of water?

    <p>0.05 kg ai/ha</p> Signup and view all the answers

    When calculating the number of loads needed, what does the size of the sprayer represent?

    <p>The amount of liquid the sprayer can hold</p> Signup and view all the answers

    In the context of spray solutions, what does WP stand for?

    <p>Wettable Powder</p> Signup and view all the answers

    To achieve a 0.04% concentration in a spray solution, which of the following would be correct?

    <p>Use 0.04 grams of active ingredient per liter of water</p> Signup and view all the answers

    What is the primary goal in managing weeds in agriculture?

    <p>Formulating an efficient method to control weeds</p> Signup and view all the answers

    Which of the following effects of weeds can be considered beneficial?

    <p>They prevent soil erosion in sloping areas</p> Signup and view all the answers

    What defines a plant as a weed?

    <p>A plant that interferes with human interests or has no economic value</p> Signup and view all the answers

    Which organization focuses specifically on weed science in the Asia-Pacific region?

    <p>Asian Pacific Weed Science Society (APWSS)</p> Signup and view all the answers

    What is a major adverse effect of weeds in agricultural settings?

    <p>They increase costs for insect and disease control</p> Signup and view all the answers

    What basis is NOT typically used for classifying weeds?

    <p>Size of the weed plant</p> Signup and view all the answers

    How many species of weeds are estimated to cause serious agricultural losses worldwide?

    <p>Approximately 18,000</p> Signup and view all the answers

    Which is NOT considered a detrimental effect of weeds?

    <p>They can provide habitat for wildlife</p> Signup and view all the answers

    What effect does a depth of 5.1 cm have on the germination of certain weed species?

    <p>Significantly reduces germination of specific weed species</p> Signup and view all the answers

    Which stage of weed growth is considered the most practical phase for control measures?

    <p>The seedling stage</p> Signup and view all the answers

    What is one major factor affecting seedling growth and development?

    <p>Soil nutrient levels</p> Signup and view all the answers

    Which climatic factor is crucial for the germination and growth of weeds?

    <p>Humidity</p> Signup and view all the answers

    What characteristic is primarily responsible for the competitive power of most weeds?

    <p>Rapid development</p> Signup and view all the answers

    Why are roots of seedlings more susceptible to herbicide absorption?

    <p>They have thin epidermal walls</p> Signup and view all the answers

    What role do light conditions play in weed adaptation?

    <p>They affect germination and flowering time</p> Signup and view all the answers

    What is persistence in weeds primarily a result of?

    <p>Adaptive potential to environments</p> Signup and view all the answers

    Which plant is classified as a basophilic species?

    <p>Agropyron repens</p> Signup and view all the answers

    How do biotic factors primarily affect weed growth?

    <p>Through competition for available resources</p> Signup and view all the answers

    What characteristic distinguishes allelopathy from competition?

    <p>Depends on chemical compounds being released into the environment</p> Signup and view all the answers

    Which of the following weed species is noted for accumulating significant amounts of nitrogen?

    <p>Amaranthus viridis</p> Signup and view all the answers

    Which of these factors does NOT influence the competitive ability of weeds against crops?

    <p>Wind velocity</p> Signup and view all the answers

    What type of soil conditions do Acidophiles prefer?

    <p>Acidic soil conditions</p> Signup and view all the answers

    Which method can discourage specific weeds such as nutsedge?

    <p>Repeated cultivation</p> Signup and view all the answers

    What is the primary nutrient that Achyranthus aspera is known to accumulate?

    <p>Phosphorus</p> Signup and view all the answers

    What is a primary characteristic of physical dormancy in weed seeds?

    <p>Inability to absorb moisture due to seed coat impermeability</p> Signup and view all the answers

    Which type of dormancy is acquired as seeds mature?

    <p>Primary (natural) dormancy</p> Signup and view all the answers

    What method is used to break the physical dormancy of hard-shelled seeds?

    <p>Scarification</p> Signup and view all the answers

    What effect does sunlight have on weed seed viability?

    <p>Reduces moisture content, leading to seed death</p> Signup and view all the answers

    Which of the following weed seeds is reported to remain viable for the longest time?

    <p>Nelumbo nucifera</p> Signup and view all the answers

    Which factor is shown to be more detrimental to seed viability?

    <p>Soil type, specifically peat soil</p> Signup and view all the answers

    Which mechanism is NOT associated with physiological dormancy in weed seeds?

    <p>Impermeability of the seed coat</p> Signup and view all the answers

    Which of the following is an example of a species with reported longevity in seed viability?

    <p>Cyperus rotundus</p> Signup and view all the answers

    How many kilograms of commercial formulation are needed to treat a 2-ha area with a recommended rate of 0.5 kg ai/ha and a 3% active ingredient concentration?

    <p>33.33 kg</p> Signup and view all the answers

    What is the correct amount of chemical needed to dilute 750 ml of water to achieve a concentration of 0.2% using a chemical with 50% a.i.?

    <p>3 g</p> Signup and view all the answers

    If the total cost of 1000 ml of chemical is P 450, what is the cost for 3 g of this chemical?

    <p>P 1.35</p> Signup and view all the answers

    What is the recommended first step in calibrating a knapsack sprayer?

    <p>Check for leaks and clear nozzles</p> Signup and view all the answers

    What volume of spray solution is needed per hectare if 300 liters are used on a 0.5-ha area?

    <p>600 liters</p> Signup and view all the answers

    What is the relationship formula to determine the amount of chemical needed to dilute a specific volume of water?

    <p>$Y = (X imes Z) / 1,000,000$</p> Signup and view all the answers

    During calibration, how will you calculate the application rate in liters per hectare?

    <p>Application Rate = (Swath Established imes Distance Traveled) / 10,000</p> Signup and view all the answers

    When calculating the amount of chemical needed, what unit is effectively used for the volume of water?

    <p>Liters</p> Signup and view all the answers

    What is the primary goal of weed science?

    <p>To formulate the most effective and affordable methods of weed control</p> Signup and view all the answers

    Which of the following is classified as a detrimental effect of weeds?

    <p>Reduced crop yield due to competition for resources</p> Signup and view all the answers

    According to life cycle classification, which of the following is NOT a type of weed?

    <p>Permanent weeds</p> Signup and view all the answers

    What impact do weeds generally have on the quality of agricultural products?

    <p>They lead to decreased quality due to competition and contamination</p> Signup and view all the answers

    Which of the following is a beneficial effect of weeds?

    <p>Weeds help prevent soil erosion in sloping areas</p> Signup and view all the answers

    What is a commonly accepted definition of weeds?

    <p>Plants that interfere with human activities or desirable plants</p> Signup and view all the answers

    Which organization is associated with weed science in the Asia-Pacific region?

    <p>Asian Pacific Weed Science Society</p> Signup and view all the answers

    How many weed species are estimated to cause serious economic losses worldwide?

    <p>Around 18,000</p> Signup and view all the answers

    Which weed species is noted for having the longest reported seed longevity?

    <p>Nelumbo nucifera</p> Signup and view all the answers

    What type of dormancy is characterized by seeds acquiring it as they develop?

    <p>Primary dormancy</p> Signup and view all the answers

    Which factor is most detrimental to the viability of weed seeds?

    <p>Sunlight exposure</p> Signup and view all the answers

    Which type of mechanism breaks down the impermeability of a seed coat during dormancy?

    <p>Physical (structural) mechanism</p> Signup and view all the answers

    What is the maximum reported moisture content (m.c.) for Cyperus rotundus that can still allow seed viability?

    <p>13% to 16%</p> Signup and view all the answers

    Which of the following is a method for breaking physical dormancy in seeds with hard seed coats?

    <p>Scarification</p> Signup and view all the answers

    Which of the following species has been recorded to have a seed longevity of up to 19 years in glass vials?

    <p>Amaranthus spinosus</p> Signup and view all the answers

    Which type of dormancy results from unfavorable conditions encountered by seeds?

    <p>Secondary dormancy</p> Signup and view all the answers

    What effect does 5.1 cm soil depth have on the germination of certain weed species?

    <p>Reduces germination in Echinochloa crusgalli, Brachiaria, and Sesbania</p> Signup and view all the answers

    At which stage is a weed most vulnerable to management practices?

    <p>Seedling stage</p> Signup and view all the answers

    Which factor does NOT influence the competitive power of a weed?

    <p>Increased soil moisture</p> Signup and view all the answers

    What role does light play in the germination and growth of weeds?

    <p>Affects flowering time and seed maturation</p> Signup and view all the answers

    What is a primary reason that seedlings are more susceptible to herbicides?

    <p>Absence of cutin or waxes on leaves</p> Signup and view all the answers

    Which climatic factor is most significant in determining weed persistence?

    <p>Sunlight duration</p> Signup and view all the answers

    What adaptive potential allows weeds to grow in diverse environments?

    <p>Adaptive persistence</p> Signup and view all the answers

    Which statement is true regarding seedling growth and development factors?

    <p>Soil pH and nutrient level are critical</p> Signup and view all the answers

    How many liters of commercial formulation are needed to treat a 0.5-ha area with a 0.04% concentration fungicide when the volume of spray required is 150 liters?

    <p>0.12 liters</p> Signup and view all the answers

    What is the correct formula to calculate the commercial formulation in kg for a recommended rate of 0.75 kg ai/ha over a 0.5-ha area with a 70% active ingredient formulation?

    <p>Recommended rate x area / % a.i.</p> Signup and view all the answers

    How many kilograms of commercial formulation are required for treating a 0.5-ha area based on a recommended rate of 0.75 kg ai/ha with a 70% active ingredient formulation?

    <p>0.536 kg</p> Signup and view all the answers

    What is the total volume of spray needed for a 0.5-ha area if the application rate is 350 liters/ha?

    <p>175 liters</p> Signup and view all the answers

    If a 16-liter sprayer is used, how much active ingredient is delivered per sprayer load if 0.536 kg of commercial formulation is used over a total spray volume of 175 liters?

    <p>0.049 kg</p> Signup and view all the answers

    Which component is NOT necessary to calculate the amount of pesticide granules to apply?

    <p>Type of plant being treated</p> Signup and view all the answers

    What is the recommended spray concentration used in the application of a fungicide if the effective concentration is set at 0.04%?

    <p>0.04%</p> Signup and view all the answers

    What is the total active ingredient needed when pesticide granules are applied at a rate of 0.5 kg ai/ha to a 2-ha field?

    <p>1 kg</p> Signup and view all the answers

    What is the total volume of spray needed for treating a 0.6-ha field at a rate of 300 liters/ha using a 16-liter sprayer?

    <p>11.25 loads</p> Signup and view all the answers

    To achieve a 0.21% concentration, how much 70% WP product must be added to 16 liters of water?

    <p>5 tbsp</p> Signup and view all the answers

    How is the number of sprayer loads determined to achieve a desired spray volume?

    <p>By dividing the desired spray volume by the size of the sprayer</p> Signup and view all the answers

    What is the % concentration if 20 grams of a 50% WP product is added to 5 gallons of water?

    <p>0.05%</p> Signup and view all the answers

    How many loads are required for a 0.5-ha area when aiming for a spray volume of 160 liters/ha with a 16-liter sprayer?

    <p>10 loads</p> Signup and view all the answers

    If 15 ml of a 30% EC product is added to 20 liters of water, what is the % concentration?

    <p>0.02%</p> Signup and view all the answers

    Which formula is used to convert weight recommendations to percent concentration in the solution?

    <p>% concentration = weight of product x concentration / volume of solution</p> Signup and view all the answers

    How many loads are required to spray a 0.4-ha field at a rate of 400 liters/ha using a 16-liter sprayer?

    <p>12 loads</p> Signup and view all the answers

    What is the maximum lifespan of biennial weeds?

    <p>2 years</p> Signup and view all the answers

    Which of the following plant types has narrow, 2-ranked leaves and a round stem?

    <p>Grasses</p> Signup and view all the answers

    Which category do weeds that can grow on both cultivated land and wild areas belong to?

    <p>Facultative weeds</p> Signup and view all the answers

    Which of the following is an example of a perennial weed?

    <p>Cynodon dactylon</p> Signup and view all the answers

    What type of aquatic weed has its roots under the water but leaves above the surface?

    <p>Emerged</p> Signup and view all the answers

    What is a characteristic feature of sedges that distinguishes them from grasses?

    <p>Triangular stem shape</p> Signup and view all the answers

    What is the goal of weed science as a discipline?

    <p>To formulate efficient methods for controlling weeds</p> Signup and view all the answers

    Which of the following is NOT a beneficial effect of weeds?

    <p>Interfering with crop growth</p> Signup and view all the answers

    How long do perennial weeds typically live?

    <p>3 years or more</p> Signup and view all the answers

    What classification basis for weeds is mentioned in the content?

    <p>Life cycle</p> Signup and view all the answers

    Which of the following weeds is noted for having broadleaf and netted venation?

    <p>Amaranthus spinosus</p> Signup and view all the answers

    How many weed species are estimated to cause serious losses worldwide?

    <p>18,000</p> Signup and view all the answers

    Which journal is specifically focused on weed science?

    <p>Weed Research</p> Signup and view all the answers

    What is a commonly accepted definition of weeds?

    <p>Plants that interfere with human interests</p> Signup and view all the answers

    Which of the following societies is associated with weed science in Asia?

    <p>Asian Pacific Weed Science Society</p> Signup and view all the answers

    What is one of the adverse effects of weeds on crops?

    <p>Reduced crop yield due to nutritional competition</p> Signup and view all the answers

    What is the main feature of eradication measures in weed control?

    <p>They aim to completely eliminate weed species and their seeds from an area.</p> Signup and view all the answers

    How do control measures in weed management typically function?

    <p>They minimize weed intensity to protect crop yield without elimination.</p> Signup and view all the answers

    Which of the following describes cultural weed management methods?

    <p>Planning land use in ways that promote competitive crop advantage.</p> Signup and view all the answers

    Which method is NOT categorized as a mechanical method for weed control?

    <p>Fumigation</p> Signup and view all the answers

    What is the characteristic outcome of mechanical weed control methods?

    <p>They provide an immediate physical removal of weeds.</p> Signup and view all the answers

    In which scenario is eradication most likely to be attempted?

    <p>When a weed species is newly introduced and poses a high risk.</p> Signup and view all the answers

    Which of the following statements best describes the relationship between weed control and weed management?

    <p>Weed management is a comprehensive approach that includes weed control among other strategies.</p> Signup and view all the answers

    Which factor significantly influences the choice of weed management strategies?

    <p>The economic value of crops affected by weeds.</p> Signup and view all the answers

    What is the principle behind integrated weed management (IWM)?

    <p>Employing a variety of control methods for effective weed control.</p> Signup and view all the answers

    Which method utilizes living organisms to manage pest populations?

    <p>Biological control</p> Signup and view all the answers

    What is a significant advantage of integrated weed management (IWM)?

    <p>It prevents the development of resistance in weeds to herbicides.</p> Signup and view all the answers

    Which of the following factors is NOT relevant to chemical methods of weed control?

    <p>Type of sprayer used</p> Signup and view all the answers

    In pesticide calculations, which factor is essential for determining the spray volume per hectare?

    <p>The size of the sprayer, area of field, and number of loads.</p> Signup and view all the answers

    What is the conversion factor for area when measuring in hectares?

    <p>1 hectare = 10,000 square meters</p> Signup and view all the answers

    What type of weeds are best targeted for biological control?

    <p>Introduced weeds</p> Signup and view all the answers

    How do you convert grams per liter (g/liter) to a percentage concentration?

    <p>Divide by 10</p> Signup and view all the answers

    What role does competition for moisture primarily play between weeds and crops?

    <p>Weeds transpire more water than most crop plants.</p> Signup and view all the answers

    How does planting density of crops influence competition with weeds?

    <p>Increased crop density reduces weed competitiveness until self-competition occurs.</p> Signup and view all the answers

    Which type of weeds are more likely to outcompete C3 crops in terms of CO2 utilization?

    <p>C4 type weeds</p> Signup and view all the answers

    What impact does dense weed growth have on the leaf area development of crops?

    <p>It reduces leaf area development.</p> Signup and view all the answers

    Which factor does NOT directly affect the competitive ability of crops against weeds?

    <p>The climatic conditions.</p> Signup and view all the answers

    What is a potential consequence of weed competition on crop pest and disease incidence?

    <p>Increased pest and disease incidence on crops due to weeds.</p> Signup and view all the answers

    How do fast canopy forming crops generally relate to weed competition?

    <p>They suffer less from weed competition than slow-growing crops.</p> Signup and view all the answers

    What happens to crop yields as weed density increases?

    <p>Crop yields typically decrease with increased weed density.</p> Signup and view all the answers

    What is the first phase of seed germination that involves the absorption of water by the endosperm?

    <p>Imbibition</p> Signup and view all the answers

    Which type of germination involves the cotyledons remaining below the soil surface?

    <p>Hypogeal germination</p> Signup and view all the answers

    Which chemical treatment is commonly used to break down seed dormancy?

    <p>Sulfuric acid</p> Signup and view all the answers

    What is the primary purpose of the stratification method in seed treatment?

    <p>To simulate natural conditions for germination</p> Signup and view all the answers

    During germination, what is primarily responsible for the rapid metabolic activity of the embryo?

    <p>Water absorption</p> Signup and view all the answers

    Which environmental factor is critical for the hydrolysis of food reserves in seeds during germination?

    <p>Moisture</p> Signup and view all the answers

    Which period of germination is observed when the root or root-like structures grow into the soil?

    <p>Root elongation</p> Signup and view all the answers

    What type of treatment applies light and temperature to aid artificial breaking of seed dormancy?

    <p>Growth regulation</p> Signup and view all the answers

    Which weed has the longest longevity of seed viability based on the provided data?

    <p>Nelumbo nucifera</p> Signup and view all the answers

    Which factor has been found to be detrimental to seed viability?

    <p>Exposure to sunlight</p> Signup and view all the answers

    What is the primary type of dormancy that a seed may acquire during its development?

    <p>Natural dormancy</p> Signup and view all the answers

    What mechanism primarily prevents a seed's ability to absorb water and oxygen?

    <p>Physical mechanism</p> Signup and view all the answers

    Which process is used to break the physical dormancy of hard-shelled seeds?

    <p>Scarification</p> Signup and view all the answers

    In which soil type were weed seeds found to have lower viability?

    <p>Peat soil</p> Signup and view all the answers

    What type of mechanism is responsible for dormancy caused by an immature embryo?

    <p>Physiological mechanism</p> Signup and view all the answers

    Which of the following seed types demonstrates primary dormancy?

    <p>Generally mature seeds</p> Signup and view all the answers

    Which factors are influential in determining the potential of allelochemicals?

    <p>Soil and air temperature</p> Signup and view all the answers

    Which principle focuses on preventing the establishment and spread of weeds?

    <p>Prevention</p> Signup and view all the answers

    What is a specific negative effect of Sour Orange on weed growth?

    <p>Inhibits seed germination of bermuda grass</p> Signup and view all the answers

    Which of the following best describes the goal of weed management systems?

    <p>Maintain an environment detrimental to weeds</p> Signup and view all the answers

    What effect does Leucaena have on crop yields?

    <p>Reduces yield of wheat while increasing yield of maize</p> Signup and view all the answers

    What is the ideal scenario for applying eradication measures to control weeds?

    <p>In smaller areas with extremely noxious and persistent weed species</p> Signup and view all the answers

    Which of the following measurements are part of a long-term weed control plan?

    <p>Regular crop rotation</p> Signup and view all the answers

    Which of the following is considered a mechanical method of weed control?

    <p>Hand pulling</p> Signup and view all the answers

    Which of the following weed control methods is considered curative?

    <p>Weed seed sterilization</p> Signup and view all the answers

    What is a common practice to prevent weed introduction onto farms?

    <p>Clean machinery thoroughly before moving it between fields</p> Signup and view all the answers

    What is the main difference between weed control and weed management?

    <p>Weed management involves planning ahead to minimize weed invasions</p> Signup and view all the answers

    Which method can be used to destroy dormant viable weed seeds in the soil?

    <p>Flooding and fumigation</p> Signup and view all the answers

    Which among the following is NOT a type of weed control method?

    <p>Aspectual methods</p> Signup and view all the answers

    What is one reason that eradication measures are rarely achieved?

    <p>High cost and difficulty involved</p> Signup and view all the answers

    In weed control, what is the aim of cultural methods?

    <p>To reduce weed population through agricultural practices</p> Signup and view all the answers

    What is the purpose of mechanical methods in weed control?

    <p>To destroy weeds by physical intervention</p> Signup and view all the answers

    How many liters of the commercial formulation are required for treating a 0.5-ha area with a 0.04% concentration fungicide and a total spray volume of 150 liters?

    <p>0.12 liters</p> Signup and view all the answers

    What is the total volume of spray needed for a 0.5-ha area if 350 liters of spray solution are applied per hectare?

    <p>175 liters</p> Signup and view all the answers

    If the recommended rate for a pesticide is 0.75 kg ai/ha, how much is required for a 0.5-ha area with a 70% a.i. formulation?

    <p>0.536 kg</p> Signup and view all the answers

    Which formula represents how to calculate the amount of commercial formulation needed based on the recommended rate (kg a.i./ha)?

    <p>recommended rate x area / % a.i. in formulation</p> Signup and view all the answers

    What amount of active ingredient is delivered per sprayer load if 0.536 kg of commercial formulation is used in a 16-liter sprayer for a total spray volume of 175 liters?

    <p>0.049 kg</p> Signup and view all the answers

    When applying pesticide granules at a rate of 0.5 kg ai/ha to a 2-ha field, what is the total active ingredient required?

    <p>1 kg</p> Signup and view all the answers

    What is the volume of spray needed for treating a 0.5-ha area if the application rate is 350 liters/ha?

    <p>175 liters</p> Signup and view all the answers

    If using a 50% a.i. formulation, how much commercial formulation is needed if the target spray concentration is 0.04% for a 0.5-ha area?

    <p>0.12 liters</p> Signup and view all the answers

    What is a primary goal of crop protection in weed science?

    <p>Formulating effective and efficient weed control methods</p> Signup and view all the answers

    Which of the following is considered a beneficial effect of weeds?

    <p>Weeds provide excellent forage for animals</p> Signup and view all the answers

    Which classification of weeds is based on their life cycle?

    <p>Biennial weeds</p> Signup and view all the answers

    What defines the controversy around weeds?

    <p>Weeds can have both positive and negative impacts depending on perspective</p> Signup and view all the answers

    What are the organizations associated with weed science in Asia?

    <p>International Weed Science Society</p> Signup and view all the answers

    Which of the following effects do weeds have on agriculture?

    <p>Weeds contribute to higher maintenance costs</p> Signup and view all the answers

    How are weeds defined in the context of agriculture?

    <p>Plants that grow out of place and interfere with human interests</p> Signup and view all the answers

    Which of the following is NOT typically included as an adverse effect of weeds?

    <p>Improvement of soil structure</p> Signup and view all the answers

    What is a main characteristic of biennial weeds?

    <p>They require two growing seasons to complete their life cycle.</p> Signup and view all the answers

    Which of the following is an example of a perennial weed?

    <p>Cynodon dactylon</p> Signup and view all the answers

    What distinguishes sedges from grasses?

    <p>Sedges have three-ranked leaves and triangular stems.</p> Signup and view all the answers

    Which type of weed is characterized by living in cultivated areas only?

    <p>Obligate weeds</p> Signup and view all the answers

    Which of the following classifications of weeds is based on their growth environment?

    <p>Habitat classification</p> Signup and view all the answers

    What type of broadleaf weed would you find with netted venation?

    <p>Broadleaf weeds</p> Signup and view all the answers

    What is a defining feature of free-floating aquatic weeds?

    <p>They float on the water surface and are not rooted.</p> Signup and view all the answers

    Which of the following terms describes weeds that can exist in both cultivated and wild environments?

    <p>Facultative weeds</p> Signup and view all the answers

    What is a key characteristic of cultivated soil in relation to allelopathy?

    <p>It has higher values of allelopathy.</p> Signup and view all the answers

    Which of the following practices is essential for effective weed prevention?

    <p>Thoroughly cleaning farm machinery before moving it.</p> Signup and view all the answers

    Which plant is noted for inhibiting the sprouting of purple nut sedge tubers?

    <p>Mango</p> Signup and view all the answers

    What are abiotic and biotic stresses known to influence?

    <p>The activity of allelochemicals in soil.</p> Signup and view all the answers

    Which principle of weed control focuses on long-term planning to reduce weed infestation?

    <p>Prevention</p> Signup and view all the answers

    Which of the following allelopathic plants inhibits root growth and seed germination of pigweed?

    <p>Sour Orange</p> Signup and view all the answers

    How do herbicides contribute to a weed management system?

    <p>By complementing preventive and curative measures.</p> Signup and view all the answers

    Which of the following describes the interaction of weeds with crops in terms of resource competition?

    <p>Weeds compete with crops primarily for water and light.</p> Signup and view all the answers

    What is the main advantage of integrated weed management (IWM) over traditional methods?

    <p>It combines multiple control methods for effective weed control.</p> Signup and view all the answers

    Which of the following methods relies on using living organisms to control pest populations?

    <p>Biological methods</p> Signup and view all the answers

    What is one of the major characteristics of biennial weeds?

    <p>They require two growing seasons to mature.</p> Signup and view all the answers

    What is the definition of blind tillage?

    <p>Tillage carried out after a crop has emerged.</p> Signup and view all the answers

    Which of the following is considered a disadvantage of using herbicides?

    <p>They can lead to resistance in weed populations.</p> Signup and view all the answers

    In pesticide calculations, how do you convert grams per liter to percentage concentration?

    <p>Divide by 10</p> Signup and view all the answers

    What is the purpose of using solarization in weed management?

    <p>To desiccate and reduce weed populations.</p> Signup and view all the answers

    Which factor is NOT important in achieving effective integrated weed management?

    <p>Exclusivity of chemical methods</p> Signup and view all the answers

    What is primarily reduced in crop performance due to weed competition?

    <p>Leaf area development</p> Signup and view all the answers

    Which statement best describes the effect of weed density on crop yield?

    <p>Increased weed density generally results in decreased crop yield.</p> Signup and view all the answers

    How does the type of weed species affect crop competition?

    <p>Different weed species have varying competitive abilities against crops.</p> Signup and view all the answers

    What competitive advantage do C4 type weeds have over C3 type crops?

    <p>More efficient utilization of CO2</p> Signup and view all the answers

    Which of the following factors contributes significantly to crop-weed competition?

    <p>Weed species variety</p> Signup and view all the answers

    What role does crop density play in relation to weed competition?

    <p>Increased crop density can suppress weed growth.</p> Signup and view all the answers

    What impact does dense weed growth have on crop seedlings?

    <p>Prevents sunlight from reaching the seedlings.</p> Signup and view all the answers

    Which characteristic of crops may influence their competitive ability against weeds?

    <p>Canopy formation</p> Signup and view all the answers

    What characterizes a noxious weed?

    <p>It is highly competitive and persistent.</p> Signup and view all the answers

    Which factor is primarily responsible for the establishment of a weed species?

    <p>Magnitude of viable weed seed reserve.</p> Signup and view all the answers

    What effect does nitrogenous fertilizer typically have on weed seeds?

    <p>It enhances weed seed germination rates.</p> Signup and view all the answers

    Which of the following countries has the highest estimated number of weed seeds per hectare?

    <p>Germany</p> Signup and view all the answers

    What was the outcome when Scirpus maritimus was present in rice crops?

    <p>It reduced rice yields by 70% at certain densities.</p> Signup and view all the answers

    How does constant cultivation affect weed seed reserves?

    <p>It decreases weed seed reserves.</p> Signup and view all the answers

    Which cropping system is noted to reduce weed seed population effectively?

    <p>Sugar beets followed by beans.</p> Signup and view all the answers

    What is the significance of determining weed seed populations in the soil?

    <p>It indicates the efficiency of weed control methods.</p> Signup and view all the answers

    What is the maximum lifespan of biennial weeds?

    <p>1 to 2 years</p> Signup and view all the answers

    Which of the following weeds is classified as an annual weed?

    <p>Echinochloa spp.</p> Signup and view all the answers

    What distinguishes sedges from grasses?

    <p>Triangular stem structure</p> Signup and view all the answers

    What type of aquatic weed has its roots underwater and leaves growing above the surface?

    <p>Emerged</p> Signup and view all the answers

    Which plant is an example of a perennial weed?

    <p>Cyperus rotundus</p> Signup and view all the answers

    What characterizes broadleaf weeds?

    <p>Broad leaves with netted venation</p> Signup and view all the answers

    Which of the following is classified as an obligate weed?

    <p>Pistia stratiotes</p> Signup and view all the answers

    Which of the following statements about perennial weeds is true?

    <p>They live three years or more.</p> Signup and view all the answers

    Which crop characteristic contributes to reduced weed competition?

    <p>Fast canopy formation</p> Signup and view all the answers

    What defines the competition for space in crop-weed interactions?

    <p>The requirement for CO2</p> Signup and view all the answers

    What is an important effect of increased weed density on crop yield?

    <p>Decline in crop yield</p> Signup and view all the answers

    Which weed type is mentioned as having better CO2 utilization efficiency?

    <p>C4 type weeds</p> Signup and view all the answers

    Under which condition does competition for light become most critical in crops?

    <p>When moisture is plentiful</p> Signup and view all the answers

    What is the main purpose of integrated weed management (IWM)?

    <p>To achieve economic and effective weed control</p> Signup and view all the answers

    How does the type of weed species affect crop competition?

    <p>By influencing nutrient access</p> Signup and view all the answers

    What is a consequence of crop competition with weeds concerning pest and disease incidence?

    <p>Heightened disease susceptibility</p> Signup and view all the answers

    Which method is particularly useful in targetting introduced weed species?

    <p>Biocontrol using bioagents</p> Signup and view all the answers

    How does crop density impact weed growth and competition?

    <p>More crops lead to reduced weed growth</p> Signup and view all the answers

    What is NOT an advantage of integrated weed management (IWM)?

    <p>Creates herbicide residue in soil</p> Signup and view all the answers

    What is the formula to calculate spray volume in liters per hectare?

    <p>Size of sprayer x Number of sprayer loads / Area of field</p> Signup and view all the answers

    What is the primary use of herbicides in weed management?

    <p>To kill or control weed growth</p> Signup and view all the answers

    Which of the following describes the biological method of weed management?

    <p>It employs living organisms to suppress weed populations</p> Signup and view all the answers

    In pesticide calculations, how many grams are in one kilogram?

    <p>1,000 grams</p> Signup and view all the answers

    Which statement best describes the solarization method?

    <p>Uses solar energy for desiccating weeds</p> Signup and view all the answers

    How much commercial formulation is needed to treat a 2-ha area with a recommended rate of 0.5 kg ai/ha when the formulation contains 3% active ingredient?

    <p>33.33 kg</p> Signup and view all the answers

    What is the amount of chemical needed to reach a desired concentration of 300 ppm in 500 ml of water?

    <p>0.15 g</p> Signup and view all the answers

    If a chemical has a 50% active ingredient concentration, how much is needed to dilute 750 ml of water to a concentration of 0.2%?

    <p>3 g</p> Signup and view all the answers

    What is the cost of the chemical required if 3 g is needed and the price is P 450 for 1000 ml or g?

    <p>P 1.35</p> Signup and view all the answers

    Which equation would you use to find the application rate in liters per hectare after performing a test run with a knapsack sprayer?

    <p>Application rate (li/ha) = Volume sprayed (li) / Area Sprayed (ha)</p> Signup and view all the answers

    What initial step is crucial for calibration when using a knapsack sprayer?

    <p>Clean the nozzle and check for leaks</p> Signup and view all the answers

    When using the equation ‘X’ ppm = ‘Y’ amount of chemical / ‘Z’ (volume of water), what does ‘Y’ represent?

    <p>The amount of chemical needed</p> Signup and view all the answers

    For a fungicide application rate of 3 tbsp per 16 liters of water, how would you convert this rate to ppm for a 500 ml dilution?

    <p>300 ppm</p> Signup and view all the answers

    Study Notes

    Weed Classification based on Life Cycle

    • Annual weeds complete their life cycle within one year, with examples such as Echinochloa spp., Ipomea triloba, and Amaranthus spinosus.
    • Biennial weeds live for more than one year but not more than two years requiring two growing seasons to complete their life cycle, an example is Rottboellia exaltata.
    • Perennial weeds live for three or more years, examples include Synedrella nodiflora, Cynodon dactylon (Bermuda grass), Sorghum halepense (Johnson grass), Portulaca oleracea (Pigweed), Cyperus rotundus (Purple nutsedge), and Saccharum spontaneum (Talahib).

    Weed Classification based on Morphology

    • Grasses: Identified by narrow, two-ranked leaves, parallel venation, round stems (culm), and a ligule. Examples include Rottboellia exaltata and Eleusine indica.
    • Sedges: Similar to grasses, but have three-ranked leaves, triangular stem, and are lacking a ligule. The leaf sheath fuses around the stem to form a tube. Examples are Cyperus rotundus and Cyperus iria.
    • Broadleaf weeds: Distinguished by broad leaves and netted venation. They can be either monocots or dicots. Examples are Monochoria vaginalis, Amaranthus spinosus, and Spenochlea zeylanica.

    Weed Classification Based on Habitat

    • Terrestrial weeds grow on land:
      • Obligate weeds are found only in cultivated areas.
      • Facultative weeds are found in both wild and cultivated areas.
    • Aquatic weeds grow in or near water:
      • Free-floating weeds grow on the water surface, unattached to the soil bottom. Examples include Pistia stratiotes and Azolla pinnata.
      • Emerged weeds have roots underwater and leaves above the water surface. Example is Scirpus grossus.
      • Submerged weeds typically remain underwater with some floral parts potentially appearing above the water surface. Example is Hydrilla verticillata.

    Weed Control

    • Primary objective of weed management: To create an environment unfavorable to weeds through both preventive and curative measures, either alone or combined.
    • Principles of weed control: Prevention, Eradication, Control, and Management.

    Preventive Methods

    • Emphasis on preventing weed introduction, establishment, and spread.
    • Effective preventive measures are crucial for successful weed control.
    • Long-term planning is essential for effective and economical weed control.
    • Avoid using crop seeds that are infested with weeds.
    • Avoid feeding farm animals with screenings or materials containing weed seeds.
    • Thoroughly clean farm machinery before moving it between fields.
    • Maintain cleanliness in irrigation channels, fence lines, bunds, uncropped areas, and roads.
    • Regularly inspect your farm for unfamiliar weed species.
    • Destroy new weed patches by digging deep and burning the weeds and roots.
    • Quarantine regulations are implemented in many countries to prevent the entry of weed seeds and propagules through airports and shipyards.

    Curative Methods

    • Eradication measures: Aim to completely remove all traces of a weed species, including seeds and vegetative parts, from a designated area, often a challenging and expensive process.

      • Eradication is typically attempted only in small areas due to its difficulty and cost.
      • Effective for high-value areas or when dealing with extremely noxious and persistent weeds.
      • Involves destroying the species at the initial stage of introduction and before it produces any propagules.
      • Degeneration of buried dormant seeds can be achieved through fumigation, flooding, heating, and other methods.

    • Control measures: Aim to reduce weed infestation but not necessarily eliminate it.

      • Provide a degree of weed management ranging from poor to excellent.
      • Focus on suppressing existing weed populations using physical or chemical methods.

    • Weed Management: Encompasses comprehensive land use planning in advance to minimize weed invasion and give crop plants a competitive advantage.

      • Involves a systematic approach encompassing cultural, physical, biological, and chemical methods.

    Mechanical Weed Control Methods

    • Employ cutting, removal, desiccation, and exhaustion of weeds using various techniques.
    • Examples:
      • Hand hoeing
      • Hand pulling
      • Tillage
      • Flooding
      • Burning
      • Mulching using non-living materials

    Hoeing

    • A long-standing and widely used tool for weed control.
    • Offers a cost-effective and efficient way to manage weeds.
    • Provides a supplementary tool to cultivators for row crops.

    Herbicide Application Calculations

    • To apply herbicides:

      • Determine the recommended rate (concentration of active ingredient (% ai)).
      • Calculate the desired volume of spray per treated area (liters).
      • Note the % ai present in the commercial formulation.
      • Measure the area to be treated (hectares).

    • Example:

      • To apply 300 liters of spray solution/ha to a 0.5-ha area, using a 50% EC fungicide with a recommended concentration of 0.04%, the calculation:
        • Spray volume needed for the treated area: 300 liters/ha * 0.5 ha = 150 liters.
        • Liters of commercial formulation: (150 liters * 0.04) / 50 = 0.12 liters.

    Other Herbicide Application Calculations

    • For applying pesticides with a recommended rate in kg ai/ha:

      • Determine the recommended rate (kg ai/ha).
      • Know the % ai in the formulation.
      • Measure the area to be treated (ha).

    • Example:

      • To apply 350 liters/ha of spray solution to a 0.5-ha area, using a 70% wettable powder pesticide with a recommended rate of 0.75 kg ai/ha, the calculation:
        • Commercial formulation (kg): (0.75 kg ai/ha * 0.5 ha * 100) / 70 = 0.536 kg.
        • Volume of spray needed for the treated area: 350 liters/ha * 0.5 ha = 175 liters.
        • Amount of sprayer materials/sprayer load (kg): (0.536 kg * 16 liters) / 175 liters = 0.049 kg = 49 g/sprayer load (for a 16-liter sprayer).

    Pesticide Granule Application

    • Calculate the required amount of pesticide granules using the following information:

      • Recommended rate (kg ai/ha)
      • Area to be treated (ha)
      • % ai in the granular formulation

    • Example:

      • To apply pesticide granules at a rate of 0.5 kg ai/ha to a 2-ha field, the calculation:
        • The required amount of pesticide granules:

    • (0.5 kg ai/ha * 2 ha * 100) / (percentage in the granular formulation).

    Weed Science

    • Weed science is the study of weeds and their control.
    • The goal is to develop the most efficient and least expensive way to control weeds.
    • Weed science became an official discipline in 1944, when the herbicidal properties of 2,4-D were discovered.
    • Several universities in Southeast Asia now teach weed science courses.
    • Some of these universities are in Taiwan, Malaysia, Thailand, Korea, and the Philippines.
    • There are three major weed science societies: the Asian Pacific Weed Science Society (APWSS), the International Weed Science Society (IWSS), and the Weed Science Society of the Philippines (WSSP).
    • There are several weed science journals, including Weed Research, Weed Science, and the Philippines Journal of Weed Science.

    Definitions of Weeds

    • Weeds are plants that are growing out of place, unwanted, undesirable, or useless.
    • Weeds can interfere with human activities.
    • Weeds are plants that are detrimental to agriculture.
    • Weeds have no economic value.
    • Weeds are plants whose potential for harm is greater than their potential for good.

    Adverse Effects of Weeds

    • Weeds can reduce crop yields by competing for resources, such as nutrients, water, and light.
    • Weeds can increase the cost of insect and disease control.
    • Weeds can decrease the quality of agricultural products.
    • Weeds can increase the cost of maintaining lawns and landscaping.
    • Weeds can clog irrigation and drainage canals.
    • Weeds can be a hazard to human health.

    Beneficial Effects of Weeds

    • Weeds conserve soil moisture.
    • Weeds add organic matter to the soil.
    • Weeds prevent soil erosion, especially in sloping areas.
    • Some weeds are edible.
    • Weeds can provide shelter for wildlife.
    • Weeds provide excellent forage for animals.
    • Weeds can create jobs.
    • Weeds can be used as ornamental plants.

    Classification and Identification of Weeds

    • There are over 30,000 weed species around the world, and about 18,000 species cause serious losses.

    Bases of Weed Classification

    • Life Cycle: Weeds can be classified by their life cycle, such as annual, biennial, or perennial.
    • Rainfall and Wind: Weeds have adapted to various rainfall and wind conditions.
    • Soil Factors: Some weeds prefer specific soil pH levels. Basophilic weeds prefer alkaline soil (pH 8.5), while acidophiles prefer acidic soil. Some weeds, such as Digitaria sanguinalis, prefer neutral soil.
    • Biotic Factors: Weeds interact with crops, competing for resources, and agricultural practices can influence weed populations.

    Crop-Weed Interaction

    • The two main interactions between crops and weeds are competition and allelopathy.
    • Competition: This involves the removal or reduction of essential resources from the environment, such as nutrients, moisture, light, and space.
    • Allelopathy: This involves the release of chemical compounds by plants that inhibit the growth of other plants.

    Competition

    • Weeds are better adapted to agroecosystems than crops.
    • Weeds can easily outcompete crops for resources.
    • Competition for Nutrients: Weeds absorb nutrients faster than crops and can accumulate nutrients in their tissues.
    • Competition for Moisture: Weeds transpire more water than crops.
    • Competition for Light: Dense weed growth can shade crops, hindering their growth.
    • Competition for Space: Overcrowded conditions can limit the availability of CO2 for crops. C4 weeds are more efficient at utilizing CO2 than C3 crops, giving them an advantage in competition.

    Allelopathy

    • How Allelopathy Functions: Allelopathic plants release chemicals that inhibit the growth of other plants.
    • Factors Affecting Allelopathy:
      • Plant Habitat: Cultivated soil has higher allelopathic activity than uncultivated soil.
      • Climatic Factors: Soil and air temperature and moisture levels influence the activity of allelochemicals.
      • Soil Factors: The chemical and biological properties of soil impact the presence of allelochemicals.
      • Stress Factors: Abiotic and biotic stresses can influence allelochemicals.

    Weed Control

    • A successful weed control program should consider the characteristics of the weeds, their response to environmental changes, and their reaction to herbicides.
    • The primary objective of a weed management system is to create an environment that is unfavorable for weed growth.

    Principles of Weed Control

    • Prevention: Measures taken to prevent the introduction, establishment, and spread of weeds.
    • Eradication: Eliminating existing weed populations.
    • Control: Methods used to reduce weed populations and minimize their impact.
    • Management: Implementing integrated strategies to control weeds.

    Preventive Methods

    • Prevent the introduction and spread of weeds.
    • Avoid transporting weed seeds with crops and equipment.
    • Cleaning machinery before moving it between fields.
    • Regularly inspect fields for new weed infestations.
    • Destroy any new weeds by digging them up and burning them.

    Weed Control Formulation

    • Calculating Spray Volume: The amount of spray needed per hectare (ha) is determined by:
      • Size of sprayer (liters)
      • Number of sprayer loads
      • Area of the field (ha)

    Determining Sprayer Loads

    • Formula:
      • Number of loads = (Desired spray volume (liters/ha) × Area of the field (ha))/ Size of sprayer (liters)

    Calculating Dosage

    • Percent Concentration in Solution: This refers to the percentage (by weight or volume) of the formulated product in the spray solution.
    • kg ai/ha: This refers to the amount of active ingredient (ai) per hectare.

    Calculating Percent Concentration

    • Formula:
      • % Concentration = (Weight or volume of formulated product × % ai) / (Volume of water × 1,000 [ml/liter])

    Calculating Application Rate

    • When % Concentration is Known: You can calculate the rate of application by knowing the % concentration.

    Weed Science

    • Weed science is the study of weeds and their control.
    • The goal of weed science is to find the most effective and least expensive method of weed control.
    • Weed science as a discipline began in 1944 in the United States with the discovery of the herbicidal properties of 2,4-D.
    • Weed science courses are taught in agricultural universities in Southeast Asia, including Taiwan, Malaysia, Thailand, Korea, and the Philippines.

    Weed Science Societies

    • Asian Pacific Weed Science Society (APWSS)
    • International Weed Science Society (IWSS)
    • Weed Science Society of the Philippines (WSSP)

    Journals on Weeds Science

    • Weed Research
    • Weed Science
    • Philippines Journal of Weed Science

    Definitions of WEEDS

    • Plants growing out of place.
    • Plants that are unwanted, undesirable, or useless.
    • Plants that interfere with human activities.
    • Plants that are detrimental to agriculture rather than beneficial.
    • Plants that have no economic value.
    • Plants whose virtues have not been discovered.
    • Plants which, when allowed to develop, can cause financial loss in various ways.

    Adverse Effects of WEEDS

    • Reduced crop yields due to competition for resources.
    • Increased costs for insect and disease control.
    • Reduced quality of agricultural products.
    • Increased costs of lawn maintenance and beautification projects.
    • Clogged irrigation and drainage canals.
    • Health hazards.

    Beneficial Effects of WEEDS

    • Conserve soil moisture.
    • Add organic matter to the soil.
    • Prevent soil erosion.
    • Edible, especially succulent weeds.
    • Provide shelter for wildlife.
    • Provide forage for animals.
    • Provide employment.
    • Provide patients for physicians and veterinarians.
    • Some weeds are used as ornamental plants.

    Classification and Identification of WEEDS

    • Over 30,000 weed species exist worldwide, with approximately 18,000 causing significant losses.

    Bases of WEED Classification

    According to Life Cycle

    • Annuals: Complete their life cycle in one growing season.
    • Biennials: Complete their life cycle in two growing seasons.
    • Perennials: Live for more than two growing seasons.

    Longevity of weed seeds

    • Weed seeds can remain viable in the soil for extended periods.
    • Nelumbo nucifera seeds can remain viable for up to 1,040 years.
    • Eichhornia crassipes seeds can remain viable for up to 15 years.
    • Amaranthus spinosus seeds can remain viable for up to 19 years.
    • Ageratum conyzoides seeds can remain viable for 6 to 6.5 years.

    Factors affecting the longevity of weed seeds

    • Soil type: Peat soil is more detrimental to seed viability than mineral soils.
    • Sunlight: Exposure to sunlight reduces moisture content, killing seeds.
    • Moisture content: Critical moisture content for viability differs for specific weeds.

    Dormancy of Weeds Seeds

    • Dormancy is the inability of seeds or vegetative organs to germinate under favorable conditions.

    Types of Dormancy

    • Primary (natural) dormancy: Acquired during seed development or maturation.
    • Secondary dormancy: Induced by unfavorable conditions.

    Mechanisms of Dormancy

    • Physical (structural) mechanism: Impermeability of the seed coat to water and/or oxygen.
    • Physiological mechanism: Immature embryo or presence of germination inhibitors.

    How to break dormancy

    Methods of breaking physical dormancy

    1. Scarification: Physical puncturing or breaking of the seed coat.
    2. Cultivation: Brings buried seeds to the surface, exposing them to light and oxygen.
    3. Separation: Cuts dormant tubers, rhizomes, and stolons from the mother plant, causing them to lose dormancy.

    The Seedling Stage of WEEDS

    • The most competitive stage for most weed species.
    • The most vulnerable and practical stage for control.
    • The most susceptible stage to herbicide action.

    Reasons for susceptibility to herbicide action at the seedling stage

    • Tender tissues easily absorb pre-emergence herbicides.
    • Early stage leaves are succulent, lacking cutin or waxes for herbicide protection.
    • Seedling roots have thin epidermal walls, allowing for efficient herbicide absorption.

    Major Factors affecting seedling growth and development

    • Soil factors: Nutrient level, soil pH, salinity.
    • Light: Intensity, quality, and duration.
    • Adaptation to growing conditions.
    • Competitive power of the weed: Rapid root growth, rapid leaf production, and multiple shoot development contribute to competitive advantage.

    Persistence of Weeds (adaptation)

    • Persistence is an adaptive potential that allows weeds to grow in various environments.
    • The cropping system and its management practices determine the persistence of weed species.

    FACTORS AFFECTING PERSISTENCE

    1. Climatic factors: Light, temperature, rainfall, wind, and humidity.
      • Light: Affects germination, growth, reproduction, and distribution.
      • Temperature: Affects distribution and growth.
      • Rainfall: Influences reproduction and survival.
      • Wind: Dissemination of weeds.
    2. Soil factors: Soil water, aeration, temperature, pH, fertility level, and cropping system.
      • Basophiles: Tolerate alkaline soils (pH 8.5).
      • Acidophiles: Tolerate acidic soils.
      • Neutophiles: Tolerate neutral soils.
    3. Biotic factors: Interactions with crops, agricultural practices, and other organisms.
      • Competition for resources: Weeds often outcompete crops.
      • Allelopathy: Production of chemical compounds that inhibit the growth of other plants.

    CROP-WEED INTERACTION

    • Competition: Removal or reduction of essential factors for growth.
    • Allelopathy: Production of chemicals that inhibit the growth of other plants.

    Crop-Weed Competition

    • Weeds are highly adapted to agricultural ecosystems.
    • Competition for nutrients, moisture, light, and space are the primary factors of crop production.

    Competition for Nutrients

    • Weeds absorb nutrients faster than many crop plants.
    • Nitrophills: Weeds that accumulate high levels of nitrogen (e.g., Amaranthus species).
    • ‘P’ accumulators: Weeds that accumulate high levels of phosphorus (e.g., Achyranthus aspera).
    • ‘K’ lovers: Weeds that accumulate high levels of potassium (e.g., Portulaca species).

    Weed Science

    • Weed Science studies weeds and their control to find efficient and cost-effective methods.
    • Weed Science began in 1944 in the United States with the discovery of the herbicidal properties of 2,4-D.
    • Weed Science courses are taught in some universities in Southeast Asia, including Taiwan, Malaysia, Thailand, Korea, and the Philippines.
    • Major Weed Science Societies include the Asian Pacific Weed Science Society, the International Weed Science Society, and the Weed Science Society of the Philippines.
    • Key Journals on Weed Science include Weed Research, Weed Science, and the Philippines Journal of Weed Science.

    Defining Weeds

    • Weeds are plants considered unwanted or undesirable.
    • They interfere with human activities, such as agriculture.
    • Some consider weeds as a detriment to agriculture.
    • Others believe some weeds have unrevealed benefits and value.

    Adverse Effects of Weeds

    • Weeds can reduce crop yields by competing for resources such as nutrients, water, and light.
    • They increase the cost of insect and disease control.
    • Weeds can reduce the quality of agricultural products.
    • They also increase the cost of lawn maintenance and beautification projects.
    • Weeds clog irrigation and drainage canals.
    • They can pose health hazards.

    Beneficial Effects of Weeds

    • Weeds can conserve soil moisture.
    • They add organic matter to the soil.
    • Weeds prevent soil erosion.
    • Some weeds can be used as food.
    • They provide shelter for wildlife.
    • Weeds serve as forage for animals.
    • They provide employment opportunities.
    • Some weeds are used as ornamental plants.

    Classifying and Identifying Weeds

    • Over 30,000 weed species exist globally, with approximately 18,000 causing significant losses.
    • Weeds can be classified based on their life cycle, including annual, biennial, and perennial.

    Weed Seed Longevity

    • Weed seeds can remain viable in the soil for extended periods.
    • Nelumbo nucifera seeds can remain viable for 1,040 years.
    • Eichhornia crassipes seeds can last for 15 years.

    Factors Affecting Weed Seed Longevity

    • Soil Type: Peat soil can reduce seed viability more than mineral soils.
    • Sunlight: Exposure to sunlight can kill seeds by reducing moisture content.

    Dormancy of Weed Seeds

    • Dormancy is when seeds or vegetative organs cannot germinate even under favorable conditions.
    • Dormancy can be primary (natural) or secondary, induced by unfavorable conditions.
    • Primary dormancy is acquired during seed development or maturation.
    • Secondary dormancy is triggered by unfavorable conditions.

    Mechanisms of Dormancy

    • Physical (structural) mechanism: The seed coat prevents water or oxygen penetration, such as in Celosia argentea and Ipomea triloba.
    • Physiological mechanism: Immature embryos or germination inhibitors can cause dormancy.

    Breaking Dormancy

    • Scarification: Physically puncturing or breaking the seed coat can break physical dormancy.
    • Cultivation: Bringing seeds to the surface exposes them to light and oxygen, and also separates dormant tubers from their mother plants.

    Seedling Stage

    • The seedling stage is highly competitive for most weed species.
    • This stage is also vulnerable to control measures.
    • The seedling stage is most susceptible to herbicide action.
    • Herbicides are absorbed through tender tissues of the mesocotyl, coleoptile, hypocotyl, and radicle.
    • Early seedling leaves lack protective layers, making herbicide penetration easier.
    • Seedling roots have thin epidermal walls, allowing efficient herbicide absorption.

    Factors Affecting Seedling Growth and Development

    • Soil factors: Nutrient level, soil pH, and salinity influence seedling growth.
    • Light: Light intensity, quality, and duration impact weed germination, growth, and distribution.
    • Adaptation to Growing Conditions: Weed species adapt to specific conditions.
    • Competitive Power: Weeds with rapid growth, leaf production, and multiple shoots gain a competitive advantage.

    Weed Persistence (Adaptation)

    • Persistence is a weed's ability to thrive in diverse environments.
    • The cropping system and management practices determine weed persistence.

    Factors Affecting Weed Persistence

    • Climatic factors: Climate significantly affects weed persistence, with adaptations to various temperatures, rainfall, wind, and humidity.
    • Light: Light intensity, quality, and duration impact germination, growth, and distribution.
    • Photoperiod: It influences flowering time, seed setting, and weed ecotype evolution.
    • Temperature: Both atmospheric and soil temperatures influence weed distribution.

    Calculating Spray Volume for Herbicide Application

    • Formula: liter of spray/ha = size of sprayer (liters) x no.of loads / area of field (ha)

    Calculating Sprayer Loads

    • Formula: No.of loads = desired spray volume (liters/ha) x area of field(ha) / size of sprayer (liters)

    Calculating Dosage for Foliar Sprays

    • Formula: % concentration in the solution = weight or volume of formulated product / weight or volume of water

    Calculating Rate of Application Based on % Concentration

    • The necessary information includes the recommended rate, volume, active ingredient (ai) percentage, and area to be treated.

    Calculating Rate of Application Based on kg ai/ha

    • The necessary information includes the recommended rate, active ingredient (ai) percentage, and area to be treated.

    Applying Pesticide Granules

    • The necessary information includes the recommended rate, area to be treated, and active ingredient (ai) percentage in the granular formulation.

    Weed Science

    • Weed science is the study of weeds and their control.
    • The goal of weed science is to find the most effective, efficient, and affordable way to control weeds.
    • Weed science as a discipline began in 1944 in the United States when the herbicidal properties of 2,4-D were discovered.
    • Weed science courses are taught in several agricultural universities in Southeast Asia, including Taiwan, Malaysia, Thailand, Korea, and the Philippines.

    Weed Science Societies

    • Asian Pacific Weed Science Society (APWSS)
    • International Weed Science Society (IWSS)
    • Weed Science Society of the Philippines (WSSP)

    Weed Science Journals

    • Weed Research
    • Weed Science
    • Philippines Journal of Weed Science

    Definitions of Weeds

    • Plants growing in an unwanted location.
    • Plants that are undesired, useless, or interfere with human activities.
    • Plants whose potential for harm outweighs their potential benefits.
    • Plants that are detrimental to agriculture rather than beneficial.
    • Plants that have no economic value.
    • Plants whose virtues have not been discovered.
    • Plants that can cause financial losses if allowed to develop.

    Adverse Effects of Weeds

    • Reduced crop yields due to competition for nutrients, water, and light.
    • Increased costs for insect and disease control.
    • Reduced quality of products.
    • Increased costs for lawn maintenance and beautification projects.
    • Clogged irrigation and drainage canals.
    • Health hazards.

    Beneficial Effects of Weeds

    • Soil moisture conservation.
    • Soil organic matter addition.
    • Soil erosion prevention, especially in sloping areas.
    • Food source, particularly succulent weeds.
    • Wildlife shelter.
    • Forage for animals.
    • Employment opportunities.
    • Patients for physicians and veterinarians.
    • Ornamental plant use.

    Classification and Identification of Weeds

    • Over 30,000 weed species exist worldwide, with about 18,000 causing significant losses.

    Weed Classification Bases

    • Life cycle:
      • Annual weeds: Complete their life cycle in one year. Examples: Echinochloa spp., Ipomea triloba, Amaranthus spinosus.
      • Biennials: Live for more than one year but not more than two years, requiring two growing seasons to complete their life cycle. Example: Rottboellia exaltata.
      • Perennials: Live for three or more years. Examples: Synedrella nodiflora, Cynodon dactylon (Bermuda grass), Sorghum halepense (Johnson grass), Portulaca oleracea (Pigweed), Cyperus rotundus (Purple nutsedge), Saccharum spontaneum (Talahib).
    • Morphology:
      • Grasses: Narrow, two-ranked leaves, parallel venation, round stems (culm), and presence of a ligule. Examples: Rottboellia exaltata, Eleusine indica.
      • Sedges: Similar to grasses but have three-ranked leaves, triangular stems, and lack a ligule. Leaf sheaths fuse around the stem to form a tube. Examples: Cyperus rotundus, Cyperus iria.
      • Broadleaf weeds: Broad leaves with net-like venation, either monocots or dicots. Examples: Monochoria vaginalis, Amaranthus spinosus, Spenochlea zeylanica.
    • Habitat:
      • Terrestrial weeds: Growing on land.
        • Obligate weeds: Found only in cultivated areas.
        • Facultative weeds: Found in both wild and cultivated areas.
      • Aquatic weeds: Growing in or near water.
        • Free floating: Grow on the water surface without attaching to the soil bottom. Examples: Pistia stratiotes, Azolla pinnata.
        • Emerged: Roots under the water and leaves above the surface. Example: Scirpus grossus.
        • Submerged: Normally under the water surface, but may have flowering parts above the water. Example: Hydrilla verticillata.

    Other Weed Classifications

    • Common weeds: Annual, biennial, or simple perennial weeds that are common to most farms. They are easily controlled with good farming practices.
    • Noxious weeds: Aggressive weeds that cause significant damage to crops and ecosystems.

    Weed Competition

    • Weeds compete with crops for resources like nutrients, water, light, and space (CO2), leading to reduced crop growth and yields.
    • Weed competition for moisture is significant because weeds transpire more water than crops.
    • Weed competition for light becomes crucial when moisture and nutrients are plentiful.
    • Weed competition for space (CO2) occurs under crowded plant communities.

    Factors Affecting Crop Competitive Ability Against Weeds

    • Weed density: Higher weed density leads to lower yields.
    • Crop density: Increased plant population reduces weed growth and competition until crops become self-competitive.
    • Weed species: Specific weed species influence competition. Examples: Echinochloa crusgalli in rice, Rottboellia exaltata in corn.
    • Crop species and varieties: Crops and their varieties vary in their competitive abilities against weeds. Fast canopy forming and tall crops are more resistant to weed competition than slow-growing and short-statured crops. Dwarf and semi-dwarf varieties are often more susceptible to weed competition than tall varieties.

    Weed Control Methods

    • Quarantine regulations: Implemented in most countries to prevent the entry of weed seeds and other propagules through airports and shipyards.

    Eradication Measures

    • Ideal weed control method but rarely achieved.
    • Involves completely removing a weed species, its seeds, and vegetative parts from a given area.
    • Used in high-value areas where the weed species is extremely noxious and persistent.
    • Eradication is often attempted in smaller areas like a few hectares or a few thousand square meters.

    Control Measures

    • Aim to reduce weed infestations and minimize their effects on crop yield.
    • Weed intensity is reduced but not necessarily eliminated.
    • Often achieved through physical or chemical means.

    Weed Management

    • A systematic approach that incorporates whole land use planning to minimize weed invasion and give crops a competitive advantage over weeds.

    Weed Management Methods

    • Cultural methods: Involve using farm practices to suppress weeds.
    • Physical methods: Destroy weeds through physical means.
    • Biological methods: Use living organisms (bioagents) to control weeds.
    • Chemical methods: Use herbicides to kill or control weed growth.

    Integrated Weed Management (IWM)

    • A combination of mechanical, cultural, biological, and chemical methods for effective and economical weed control.
    • Rational use of direct and indirect weed control methods for cost-effective results.
    • Flexible to incorporate new innovations and local farmer practices.
    • Developed for the entire farm.
    • Economically viable and practically feasible.

    IWM Advantages

    • Favors crop-weed competition.
    • Prevents weed shift towards a perennial nature.
    • Prevents weed resistance to herbicides.
    • Reduces herbicide residues in soil and plants.
    • Suitable for high cropping intensity.

    Pesticide Calculations

    • Simple conversion factors:
      • Area: 1 hectare (ha) = 10,000 square meters (m2)
      • Weight: 1 kilogram (kg) = 1,000 grams (g)
      • Volume: 1 liter = 1,000 milliliters (ml)
      • 1 gallon (gal) = 3.8 liters
      • 1 tablespoon = 10 ml
      • To convert g/liter to %, divide by 10.
      • To convert lb/US gallon to %, multiply by 12.
      • To convert lb/Imperial gallon to %, multiply by 10.

    Calculation Example

    • To calculate spray volume in liters per hectare, you need:
      • Size of sprayer (liters)
      • Area of field (ha)
      • Number of sprayer loads
    • Formula:
      • Liters of spray/ha = (Size of sprayer (liters) x Number of loads) / Area of field (ha)
    • Example:
      • A 16-liter sprayer is used to apply 10 loads to a 0.5-ha field.
      • Spray volume (liters/ha) = (16 liters x 10 loads) / 0.5 ha = 320 liters/ha.

    Weed Abundance

    • Scirpus supinus has a density of 2.3/m^2 in one area and 3.0 in another
    • Echinochloa crusgalli has a density of 21.3/m^2 in one area and 14.3 in another

    Weed Seed Longevity

    • Seeds from Nelumbo nucifera can remain viable for 1,040 years
    • Eichhornia crassipes seeds can remain viable for 15 years
    • Amaranthus spinosus seeds can remain viable for 19 years

    Factors Affecting Weed Seed Longevity

    • Peat soil is detrimental to weed seed viability compared to mineral soils
    • Exposure to sunlight can reduce seed moisture and kill them
    • Cyperus rotundus has a critical moisture content for viability of 13 - 16%
    • Scirpus maritimus has a critical moisture content for viability of 18%

    Weed Seed Dormancy

    • Weed seed dormancy refers to the inability of a seed to germinate under favorable conditions
    • Primary dormancy is present in newly formed seeds
    • Secondary dormancy is induced by unfavorable conditions

    Physical Dormancy

    • The seed coat can be impermeable to water and oxygen, preventing germination
    • Celosia argento and Ipomea triloba are examples of species with physical dormancy

    Physiological Dormancy

    • Dormancy can also be due to an immature embryo or germination inhibitors

    Breaking Dormancy

    • Scarification is a physical method to break dormancy by puncturing or breaking the seed coat
    • Stratification involves exposing seeds to low temperatures

    Germination

    • Germination is the resumption of active growth in an embryo, resulting in seedling emergence
    • Imbibition is the first stage of germination, where water is absorbed by the endosperm and embryo
    • Rapid metabolic activity leads to cell division and elongation
    • Roots emerge into the soil, followed by the shoot, which is the visible sign of germination

    Types of Germination

    • Hypogeal germination occurs when the cotyledons remain below ground and the plumule emerges above ground
    • Epigeal germination occurs when the cotyledons are raised above the soil
    • Monocots exhibit hypogeal germination
    • Dicots exhibit epigeal germination

    Factors Affecting Weed Germination

    • Moisture is needed for the hydrolysis of food reserves
    • Oxygen is required for respiration
    • Temperature affects both hydrolysis and respiration
    • Light can inactivate germination inhibitors

    Cultural Factors Affecting Weed Germination

    • Water management can influence growth, flooding can reduce oxygen and create anaerobic conditions
    • Allelopathy, where plants release chemicals that influence the growth of other plants, can be affected by soil type, climate, and stress factors

    Weed Control Methods

    • Prevention aims to prevent the introduction and establishment of weeds
    • Eradication aims to completely eliminate a weed species from an area
    • Control aims to reduce weed infestations, but not necessarily eliminate them
    • Management uses a system approach to minimize weed invasion and give crops a competitive advantage

    Mechanical Weed Control Methods

    • Hand hoeing and pulling
    • Tillage
    • Flooding
    • Burning
    • Mulching with non-living materials

    Chemical Weed Control

    • Herbicides are used to kill or control weeds
    • The rate of application and concentration of herbicide must be appropriate for the weed species and crop being treated

    Calculating Pesticide Application Rate

    • The amount of commercial formulation needed can be determined by the following formula:
      • Volume of spray required x Recommended spray concentration / % active ingredient in formulation
    • The amount of granular formulation can be determined by the following formula:
      • Recommended rate x Area to be treated / % active ingredient in granular formulation

    Understanding the Relationship between Weed Control and Crop Production

    • Weeds compete with crops for nutrients, water, and sunlight
    • Effective weed control can improve crop yields and reduce the need for other management practices

    Importance of Weed Control

    • Weeds can reduce crop yields, quality, and marketability
    • They can also cause health problems and damage infrastructure
    • Effective weed control is crucial for sustainable agriculture, ensuring food security, and protecting the environment

    Weed Science

    • The study of weeds and their control.
    • The goal is to develop the most effective and least expensive weed management methods.
    • Weed science emerged as a discipline in 1944 with the discovery of 2,4-D's herbicidal properties.
    • Weed science courses are offered in several Southeast Asian agricultural universities.
    • Global weed science societies include the Asian Pacific Weed Science Society (APWSS), International Weed Science Society (IWSS), and the Weed Science Society of the Philippines (WSSP).
    • Key weed science journals include Weed Research, Weed Science, and the Philippines Journal of Weed Science.

    Defining Weeds

    • Plants growing in inappropriate locations.
    • Plants that are unwanted, undesirable, or useless.
    • Plants interfering with human activities or areas of interest.
    • Plants whose potential for harm outweighs their benefits.
    • Plants detrimental to agriculture.
    • Plants lacking economic value.
    • Plants whose virtues are yet to be discovered.
    • Plants capable of causing financial loss.

    Adverse Effects of Weeds

    • Reduced crop yield due to competition for resources (nutrients, water, and light).
    • Increased costs for insect and disease control.
    • Reduced quality of agricultural products.
    • Increased lawn maintenance and beautification costs.
    • Clogging of irrigation and drainage canals.
    • Health hazards.

    Beneficial Effects of Weeds

    • Soil moisture conservation.
    • Soil organic matter addition.
    • Prevention of soil erosion, particularly in sloping areas.
    • Food source, especially succulent weeds.
    • Wildlife shelter.
    • Animal forage.
    • Employment creation.
    • Medical and veterinary patients.
    • Ornamental plant use.

    Weed Classification

    • Over 30,000 weed species exist globally, with about 18,000 causing significant losses.

    By Life Cycle

    • Annual Weeds: Complete their life cycle within one year.
      • Examples: Echinochloa spp., Ipomea triloba, Amaranthus spinosus.
    • Biennials: Live for more than one year but less than two years, requiring two growing seasons to complete their life cycle.
      • Example: Rottboellia exaltata.
    • Perennials: Live for three or more years.
      • Examples: Synedrella nodiflora, Cynodon dactylon (Bermuda grass), Sorghum halepense (Johnson grass), Portulaca oleracea (Pigweed), Cyperus rotundus (Purple nutsedge), Saccharum spontaneum (Talahib).

    By Morphology

    • Grasses: Narrow, two-ranked leaves, parallel venation, round stems (culm), and presence of a ligule.
      • Examples: Rottboellia exaltata, Eleusine indica.
    • Sedges: Similar to grasses but have three-ranked leaves, triangular stems, and lack a ligule. Leaf sheaths fuse around the stem to form a tube.
      • Examples: Cyperus rotundus, Cyperus iria.
    • Broadleaf Weeds: Broad leaves with netted venation, including monocots and dicots.
      • Examples: Monochoria vaginalis, Amaranthus spinosus, Spenochlea zeylanica.

    By Habitat

    • Terrestrial Weeds: Growing on land.
      • Obligate Weeds: Found only in cultivated areas.
      • Facultative Weeds: Found both in wild and cultivated areas.
    • Aquatic Weeds: Growing in or near water.
      • Free Floating: Grow on the water surface and are not attached to the soil bottom.
        • Examples: Pistia stratiotes, Azolla pinnata.
      • Emerged: Roots are underwater, and leaves are above the surface.
        • Example: Scirpus grossus.
      • Submerged: Generally underwater, but may have portions above the surface.
        • Example: Hydrilla verticillata.

    Other Classifications

    • Common Weeds: Annual, biennials, and simple perennials that are common in agricultural fields. They are generally controlled by good farming practices.
    • Noxious Weeds: Highly invasive and difficult to control; may require specific management strategies.

    Weed Competition

    • Weeds compete with crops for essential resources, impacting crop growth and yield.
    • Competition can be divided into four categories:
      • Competition for Nutrients: Both weeds and crops require nutrients for growth, and competition intensifies when nutrients are limited.
      • Competition for Moisture: Weeds transpire more water than most crops, increasing competition for available water.
      • Competition for Light: Dense weed growth can shade crop seedlings, significantly impacting growth.
      • Competition for Space (CO2): Crowded plant communities compete for carbon dioxide, and C4 weeds can be more efficient CO2 users, providing a growth advantage over C3 crops.

    Factors Affecting Crop-Weed Competition

    • Weed Density: Higher weed density generally translates to lower crop yield.
    • Crop Density: Increasing crop population can suppress weed growth and reduce competition until crops become self-competitive.
    • Weed Species: Different weed species have varying competitive abilities. For example, Echinochloa crusgalli in rice and Rottboellia exaltata in corn.
    • Crop Species and Varieties: Crops and their varieties differ in their ability to compete with weeds. Fast-growing and tall crops are less affected than slow-growing and shorter crops. Dwarf and semi-dwarf varieties are more susceptible to weed competition than tall varieties.

    Allelopathy

    • Allelopathy is the chemical interaction between plants, specifically the release of compounds (allelochemicals) by one plant that affect the growth of another.
    • Allelochemicals can have both positive and negative effects on crops and weeds.
    • Examples:
      • Sour Orange: Inhibits seed germination and root growth of pigweed and Bermuda grass.
      • Mango: Inhibits sprouting of purple nutsedge tubers.
      • Jungle Rice: Inhibits rice growth.
      • Crabgrass: Inhibits corn and sunflower growth.
      • Sunn Hemp (Crotolaria sp.): Inhibits lettuce growth and vegetable seed germination.
      • Leucaena: Reduces wheat and turmeric yield but increases maize and rice yield.
      • Green Spurge: Inhibits chickpea growth.
      • Jatropha curcas: Inhibits corn and tobacco growth.

    Weed Control

    • To develop a weed control program, understanding the weeds, their habitat, response to environmental changes, and herbicide reactions is crucial.
    • The primary goal of weed management is to create an environment detrimental to weeds by utilizing preventive and curative measures alone or in combination.

    Principles of Weed Control

    • Prevention: Measures to prevent weed introduction, establishment, and spread.
    • Eradication: Complete elimination of weeds from a particular area.
    • Control: Keeping weed populations below economically damaging levels.
    • Management: Ongoing strategies to prevent weed problems and maintain crop production.

    Weed Control Methods

    • Preventive Methods: Focus on pre-emptive actions to minimize weed infestation.

      • Avoiding using weed-infested crops.
      • Preventing feeding farm animals screenings or other materials containing weed seeds.
      • Thoroughly cleaning farm machinery before moving between fields.
      • Maintaining clean irrigation channels, fence lines, bunds, uncropped areas, and roads.
      • Regularly inspecting farms for new weed infestations.
      • Destroying new weed patches by digging deep and burning the plant and roots.
      • Solarization: Using solar energy to desiccate weeds.
      • Blind Tillage: Tilling soil after sowing a crop before crop plants emerge.

    • Cultural Methods: Utilizing agricultural practices to suppress weed growth.

      • Crop Rotation: Alternating crops to disrupt weed life cycles and reduce weed populations.
      • Tillage: Mechanical disturbance of the soil, either by plowing, disking, or other methods, to control weed growth.
      • Mulching: Covering soil with organic matter, such as straw or wood chips, to suppress weeds.
      • Intercropping: Planting different crops close together to reduce weed infestation.

    • Biological Methods: Using living organisms to control weed populations.

      • Biocontrol: Introducing natural enemies, like insects, diseases, herbivorous fish, snails, or competing plants to control weed populations.
      • Note: Biocontrol is not effective for all weeds and is most suitable for introduced weeds.

    • Chemical Methods: Using herbicides to kill weeds or control their growth.

      • Herbicides: Chemicals specifically designed to kill or control weed growth.
      • Types of Herbicides:
        • Pre-Emergence: Applied to the soil before weed emergence, preventing germination.
        • Post-Emergence: Applied after weeds emerge from the soil, targeting active growth.
        • Contact: Kill weeds by direct contact with the plant tissue.
        • Systemic: Absorbed by the plant and translocated throughout the system, killing the entire plant.
      • Herbicide Application: Different methods exist, including spraying, dusting, and granules.
      • Note: Use of herbicides should be monitored for potential environmental and human health impacts.

    Integrated Weed Management (IWM)

    • Combining mechanical, cultural, biological, and chemical methods for effective weed control.
    • A rational approach to minimize cost and maximize effectiveness.
    • IWM principles:
      • Flexibility: Adapting to local conditions and innovations.
      • Whole Farm Management: Addressing weed control across the entire farm.
      • Economic Viability: Cost-effective and practical.

    Advantages of IWM

    • Shifts crop-weed competition in favor of crops.
    • Prevents weeds from transitioning to a perennial nature.
    • Reduces weed herbicide resistance.
    • Minimizes herbicide residues in soil and plants.
    • Suitable for high-intensity cropping systems.

    Pesticide Calculations

    • Important Conversion Factors:

      • Area: 1 hectare (ha) = 10,000 square meters (m2)
      • Weight: 1 kilogram (kg) = 1,000 grams (g)
      • Volume: 1 liter = 1,000 milliliters (ml)
      • Gallons: 1 gallon (gal) = 3.8 liters
      • Tablespoon: 1 tablespoon = 10 ml
      • % Conversion:
        • g/liter to %: Divide by 10.
        • lb/US gallon to %: Multiply by 12.
        • lb/Imperial gallon to %: Multiply by 10.

    • Calculating Spray Volume (liters/ha):

      • Information needed: Sprayer size (liters), field area (ha), and number of sprayer loads.
      • Formula:
        • (Liter of spray/ha) = (Size of sprayer x Number of loads) / (Area of field)

    • Example:

      • A 16-liter sprayer is used with 10 loads to cover a 0.5-ha field.
      • Spray volume: (16 liters x 10 loads) / 0.5 ha = 320 liters/ha.

    Noxious Weeds

    • Noxious weeds are highly undesirable, difficult to control, and highly competitive.
    • They can cause significant damage even at low densities.
    • Scirpus maritimus reduced rice yield by 70% at 20 shoots/m2.
    • Scirpus supinus did not significantly reduce grain yield at 116 plants/m2.

    Weed Establishment

    • The abundance of viable weed seeds in the soil is a major determinant of weed establishment.
    • Weed seed germination and competition also play important roles.

    Soil as a Seed Bank

    • Germany harbors 3 to 5 billion weed seeds per hectare.
    • The Philippines has 804 million weed seeds per hectare across 12 species.
    • Minnesota has 142.3 million weed seeds per hectare.

    Factors Affecting Weed Seed Population

    • Cropping systems influence weed seed populations.
    • Sugar beets followed by beans reduce weed seed populations more than sugar beets followed by barley.
    • Nitrogenous fertilizers tend to increase weed seed populations.
    • Constant cultivation can decrease weed seed reserves in the soil.

    Annual Weeds

    • Complete their life cycle within a year.
    • Examples include Echinochloa spp., Ipomea triloba, and Amaranthus spinosus.

    Biennial Weeds

    • Live for more than one year, but not more than two years.
    • Require two growing seasons to complete their life cycle.
    • Rottboellia exaltata is an example.

    Perennial Weeds

    • Live for three or more years.
    • Examples include Synedrella nodiflora, Cynodon dactylon (Bermuda grass), Sorghum halepense (Johnson grass), Portulaca oleracea (Pigweed), Cyperus rotundus (Purple nutsedge), and Saccharum spontaneum (Talahib).

    Weed Classification by Morphology

    • Grasses: Narrow, two-ranked leaves, parallel venation, round stems (culm), and presence of a ligule. Examples include Rottboellia exaltata and Eleusine indica.
    • Sedges: Similar to grasses, but have three-ranked leaves, a triangular stem, and absence of a ligule. The leaf sheath forms a tube around the stem. Examples include Cyperus rotundus and Cyperus iria.
    • Broadleaf Weeds: Broad leaves with netted venation, can be monocots or dicots. Examples include Monochoria vaginalis, Amaranthus spinosus, and Spenochlea zeylanica.

    Weed Classification by Habitat

    • Terrestrial Weeds: Growing on land.
      • Obligate Weeds: Found only in cultivated areas.
      • Facultative Weeds: Found in both wild and cultivated areas.
    • Aquatic Weeds: Growing in or near water.
      • Free-floating Weeds: Grow on the water surface and are not attached to the soil. Examples include Pistia stratiotes and Azolla pinnata.
      • Emerged Weeds: Roots are under the water and leaves are above the water surface. Example: Scirpus grossus.
      • Submerged Weeds: Normally under the water, but may have floral parts above the water surface. Example: Hydrilla verticillata.

    Common Weeds vs. Problematic Weeds

    • Common Weeds: Annual, biennial, or simple perennial weeds common to most farms. Easily controlled with good farming practices.
    • Problematic Weeds: Examples include Cynodon dactylon (Bermuda grass), Cyperus rotundus (Purple nutsedge), and Sorghum halepense (Johnson grass). These are persistent and require more intensive management.

    Weed Competition with Crops

    • Competition for Nutrients: Weeds can deplete the soil of essential nutrients, hindering crop growth.
    • Competition for Moisture: Weeds transpire more water than many crops, reducing available moisture.
    • Competition for Light: Dense weed growth can shade crops, limiting their access to light.
    • Competition for Space (CO2): Weeds can compete for carbon dioxide, especially in crowded plant communities.

    Factors Affecting Competition

    • Weed Density: A higher density of weeds generally leads to greater competition and reduced crop yield.
    • Crop Density: Increasing crop density can suppress weed growth, but eventually, the crops will start competing with each other.
    • Weed Species: Different weed species vary in their competitive abilities.
    • Crop Species and Varieties: Crop species and varieties differ in their ability to compete with weeds. Fast-growing, tall crops generally suffer less from weed competition than slow-growing, short crops.

    Weed Control Methods

    • Mechanical Control: Tillage, hand weeding, mowing.
    • Cultural Control: Crop rotation, mulching, cover cropping.
    • Biological Control: Using living organisms to suppress weed populations. This method works best against introduced weeds.
    • Chemical Control: Using herbicides to kill or control weed growth.

    Integrated Weed Management (IWM)

    • A combination of mechanical, cultural, biological, and chemical methods to control weeds effectively and economically.
    • IWM aims for sustainable weed control and considers the whole farm ecosystem.

    Pesticide Calculations

    • Area: 1 hectare (ha) = 10,000 square meters (m2)

    • Weight: 1 kilogram (kg) = 1000 grams (g)

    • Volume: 1 liter = 1000 milliliters (ml)

    • Conversions:

      • To convert g/liter to %, divide by 10.
      • To convert lb/US gallon to %, multiply by 12.
      • To convert lb/Imperial gallon to %, multiply by 10.

    • Spray Volume Calculation:

      • Formula: Liters of spray/ha = (Size of sprayer (liters) x Number of loads) / Area of field (ha)

    • Chemical Amount Calculation for Bioassays:

      • Formula: X ppm = Y amount of chemical (g or ml) / Z (volume of water)

    Calibration for Knapsack Sprayers

    • Steps:

      1. Check for leaks and ensure the nozzle is clear.
      2. Mark out a test area.
      3. Fill the sprayer with a known amount of water.
      4. Establish the spray swath.
      5. Spray the test area.
      6. Measure the length of the test area sprayed.
      7. Calculate the application rate in liters per hectare.

    • Formula:

      • Area Sprayed (ha) = (Swath established (m) x Distance traveled (m)) / 10,000 m2/ha
      • Application rate (li/ha) = (Vol. sprayed (li)) / (Area sprayed (ha))

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