Weed Science Lecture Notes PDF

1 CROP PROTECTION (Weed Science) As a discipline. Is the study of weeds and their control. Goal: The formulation of the most satisfactory, most efficient yet least expensive method of controlling weeds....

1 CROP PROTECTION (Weed Science) As a discipline. Is the study of weeds and their control. Goal: The formulation of the most satisfactory, most efficient yet least expensive method of controlling weeds. 1944, United States – weeds science as a discipline begin when the herbicidal properties of 2,4-D was discovered. Weeds Science courses are taught in few agricultural universities of the developing Southeast Asian countries. Taiwan Malaysia Thailand Korea Philippines Weeds 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 o Plants growing out of place o Plants that are unwanted, undesirable or useless o Plants that interfere with man or areas of his interest o Plants whose potentialities for harm is greater that its potentialities for good o Plants that are detrimental to agriculture rather than beneficial o Plants that have no economic value o Plants whose virtues have not been discovered (Ralph Waldo Emerson) o Plants which when allowed to develop in the system can cause financial loss in many ways (Sagar, 1968) WEEDS are controversial plants that are neither all bad nor all good, depending on one’s outlook. Adverse Effects of WEEDS  Reduced yield of crops due to competition for nutrients, water and light.  Increased cost for insect and disease control.  Reduced quality of products.  Increased cost of lawn maintenance and beautification projects.  Clog irrigation and drainage canals.  Imposed hazards to health. Beneficial Effects of WEEDS 1. WEEDS conserve soil moisture. 2. WEEDS add organic matter to the soil. 3. WEEDS prevent soil erosion especially in sloping areas. 4. WEEDS can be used as food especially the succulent ones. 5. WEEDS provide shelter to wildlife. 6. WEEDS provide excellent forage to animals. 7. WEEDS provide employment.  2 8. WEEDS provide physician and veterinarians with patients. 9. Some WEEDS are used as ornamental plants. Classification and Identification of WEEDS There are over 30,000 weed species around the world, of which about 18,000 cause serious losses (Rodgers, 1974). Bases of WEED Classification A. According to Life Cycle 1. Annual Weeds - complete their life cycle in one year Example: Echinochloa spp. Ipomea triloba Amaranthus spinosus Echinochloa spp. Ipomea triloba Amaranthus spinosus 2. Biennials - live for more than one year but not more than 2 years - requires 2 growing seasons to complete their life cycle Example: Rottboellia exaltata 3. Perennials - live for 3 or more years Example: Synedrella nodiflora Cynodon dactylon (Bermuda grass) Sorghum halepense (Johnson grass) Portulaca oleracea (Pigweed) Cyperus rotundus (Purple nutsedge) Saccharum spontaneum (Talahib)  3 Sorghum halepense (Johnson grass) Cynodon dactylon Synedrella nodiflora Cyperus rotundus Portulaca oleracea (Pigweed) Saccharum spontaneum(Talahib) (Purple nutsedge) B. According to Morphology 1. Grasses – weeds with narrow, 2-ranked leaves, parallel venation, round stems (culm) and presence of a ligule Example: Rottboellia exaltata, Eleusine indica 2. Sedges – similar to grasses but have 3-ranked leaves and triangular stem, absence of a ligule - fusion of the leaf sheath around the stem to form a tube Example: Cyperus rotundus, Cyperus iria 3. Broadleaf weeds – weeds with broadleaf and netted venation either monocots or dicots. Example: Monochoria vaginalis, Amaranthus spinosus, Spenochlea zeylanica  4 Vegetative broadleaf plant parts Cotyledon and leaf shapes C. Based on Habitat 1. Terrestrial weeds – growing on land a. obligate weeds – found only in cultivated areas b. facultative weeds – found on both wild state and cultivated areas 2. Aquatic weeds – growing in or near water a. Free floating – weeds which grow on the water surface and not attached to the soil bottom Example: Pistia stratiotes, Azolla pinnata b. Emerged – weeds with their roots under the water and leaves above the surface Example: Scirpus grossus c. Submerged – weeds normally under water surface, but may have flora parts above the water Example: Hydrilla verticillata Other Classification 1. Common Weeds - annual, biennials, simple perennials which are more or less common to every farm - Easily controlled by good farming practices 2. Noxious Weeds - Especially undesirable characteristics - Troublesome - Difficult to control - Highly competitive character and persistent - Caused significant damage even at low densities Scirpus maritimus – reduced rice yield by 70% when present at a density of 20 shoots/m2 Scirpus supinus – did not significantly reduced grain yield at 116 plants/m2 Weed Establishment The establishment of a weed species on a particular area is determined largely by: - magnitude of viable weed seed reserve in the soil - weed seed germination - competition  5 Soil as Seed bank of Weeds Country No. of seeds/ha Author Germany 3 to 5 billion Kock (1969) (30,000 – 350,000/m² ) Philippines 804 million (12 species) Vega & Sierra (1970) Minnesota 142.3 million (4,448/sq ft) Robinson (1949) Warwick, England 204 million (top 9 inches Mercado & Lubigan soil) Bulacan, Phils. 2.75 million (275/m² ) Chancellor (1966) Echinochloa colona 5 million Matricaria recutita Factors affecting weed seed population in the soil 1. Cropping System Sugar beets followed by beans – reduced weed seed population greater than Sugar beets followed by barley 2. Fertilization Nitrogenous fertilizer tends to increase weed seed population 3. Cultivation Constant cultivation decreases weed seed reserve in the soil What is the importance of knowing weed seed populations in the soil? - The determination of the weed seed population of the soil at different times can give indications of the efficiency of weed control methods employed. Table 1. Number of weed species that germinate within a three-year period in one- gallon soil samples with or without cultivation (Vega and Sierra, 1970) SPECIES Number Counted Cultivated Uncultivated Fimbristylis miliaceae 1598.2 1275.1 Cyperus sp. 227.4 215.9 Scirpus supinus 2.3 3.0 Echinochloa crusgalli 21.3 14.3 Echinochloa colona 5.7 2.0 Sphenoclea zeylanica 39.6 38.4 Monochoria vaginalis 16.6 9.6 Jussiaea suffruticosa 1.0 2.0 Olden landia sp. 15.3 13.7 Ilysanthes antipoda 2.7 8.0 Alternanthera sp. 6.3 13.6 Unidentified broadleaf 10.0 9.3 Total 1997.7 1604.9 Longevity of weed seeds - Weed seeds can remain viable in the soil for a long time. Nelumbo nucifera – 1,040 yrs ± 120 yrs (Libby, 1951) Eichhornia crassipes – 15 years (Goss, 1974) Amaranthus spinosus – 19 years in glass vials (Juliano, 1940) Ageratum conyzoides – 6 to 6.5 years (buried in soil) Portulaca oleracea Amaranthus spinosus  6 Dactyloctenium aegyptium Mimosa pudica Factors affecting the longevity of weed seeds 1. Soil type Peat soil was found to be more detrimental to seed viability than mineral soils. 2. Sunlight Exposure to sunlight reduces moisture content below a critical level thereby killing the seed. Example: Cyperus rotundus – 13 to 16% m.c. Scirpus maritimus – 18% m.c Dormancy of Weeds Seeds Dormancy – inability of the seed or any vegetative organ to germinate under favorable conditions. Types of Dormancy 1. Primary (natural) dormancy 2. Secondary dormancy Primary (natural) dormancy - acquire as the seeds or organ develops or mature. Secondary dormancy - induced through encounter with unfavorable conditions. Mechanisms of Dormancy 1. Physical (structural) mechanism - lies mainly on the impermeability to water and/ or oxygen of the seed coat Example: Celosia argentea, Ipomea triloba 2. Physiological mechanism - due to immature embryo or presence of germination inhibitors. How to break dormancy Methods of breaking physical dormancy (seeds with hard seed coat) 1. Scarification – physical puncturing or breaking the seed coat of hard – shelled seeds.  Mechanical – abrasion, pricking, nipping and dehulling of seeds  Chemical – treatment with sulfuric acid 2. Stratification – exposure or subjecting the seeds to extremely low temperature. Methods of Breaking Physiological Dormancy 1. Natural method – “after-ripening” 2. Artificial method - treatments with germination promoters or growth regulators (KNO3, Gibberellic acid, cytokinin – like substances, auxins) - light and temperature treatments WEEDS SEED GERMINATION Germination - the resumption of the active growth of the embryo that result in the rupture of the seed coat and emergence of the young plant.  7 Process of Germination (King, 1966) 1. Imbibition * Phase I – physical process, absorption of water by the endosperm (starch) * Phase II – physiological process, water absorption by the embryo 2. Period of rapid metabolic activity - Cell division and cell elongation proceed at a fast rate supported by a rapid synthesis of materials. The end result is a perceptible growth of the embryo. 3. Root or root–like elongation - Under field condition the root or root-like structures break through the seed and grow into the soil. 4. Emergence of the shoot - Under field condition, this is considered as the first sign of weed growth. 5. Period of independent growth TYPES OF GERMINATION 1. Hypogeal germination – the cotyledons remain below the soil while the plumule pushes upward and emerge above the ground. Example: Monocots 2. Epigeal germination – the cotyledons are raised or carried above the soil where they continue to provide nutritive support to the growing embryo. Example: Dicots Types of Germination  8 1. Hypogeal germination 2. Epigeal germination - dicots - monocots Environmental factors affecting weed germination: 1. Moisture – needed in hydrolysis of food reserve. 2. Oxygen – needed in respiration or the breakdown of carbohydrates into simple sugars. 3. Temperature – needed on both hydrolysis and respiration 4. Light – inactivate the germination inhibitor. Cultural factors affecting weed germination 1. Water Management > Flooding – reduced oxygen concentration, caused the accumulation of CO2 and other gaseous products of anaerobic respiration thereby killing the embryo. > 5.1 cm depth – reduced the germination of Echinochloa crusgalli, Brachiaria, and Sesbania 2. Cultivation > Brings to the soil surface seeds buried deep in the soil expose them to light. > Aerates the soil providing oxygen to buried seeds. > Separates or cuts dormant tubers, rhizomes, stolons from their mother plant causing them to lose dormancy. The Seedling Stage of WEEDS  It is the most competitive stage in most species.  It is the most vulnerable and most practical stage for control.  It is the most susceptible stage to herbicide action. REASONS: a. Most pre-emergence herbicides are effectively absorbed through the tender tissues of the mesocotyl, coleoptile, hypocotyl and radicle. b. Leaves at the early seedling stage are succulent and still lack cutin or waxes allowing easy penetration of herbicides. c. The root of seedlings still have thin epidermal walls making herbicide absorption more efficient. Major Factors affecting seedling growth and development: 1. Soil factors  9  Nutrient Level  Soil pH  Salinity 2. Light 3. Adaptation to growing conditions 4. Competitive power of the weed - most weeds derive their competitive power from the rapid development manifested through rapid root growth, rapid leaf production, multiple shoot development allowing early photosynthetic function. Persistence of Weeds (adaptation) Persistence is an adaptive potential of a weed that enables it to grow in any environment. In an agricultural situation, the cropping system with its (associated habitat) management practices, determines the persistence of weed species. FACTORS AFFECTING PERSISTENCE 1. Climatic factors Climate has a profound effect on the persistence of weeds, which can adapt to a wide variety of climates. The important climatic factors are light, temperature, rainfall, wind and humidity. Light - Light intensity, quality and duration are important in influencing the germination, growth, reproduction and distribution of weeds. Photoperiod governs flowering time, seed setting and maturation and on the evolution of various ecotypes within a weed species. Tolerance to shading is a major adaptation that enables weeds to persist. Temperature - Temperature of atmosphere and soil affects the distribution of weeds. Rainfall - Rainfall has a significant effect on weed persistence and distribution. More rainfall or less rainfall determines reproduction and survival. Wind - Wind is a principal factor in the dissemination of weeds. 2. Soil factors - Soil factors are soil water, aeration, temperature, pH and fertility level and cropping system. Some weed species are characteristically alkali plants, known as Basophilic (pH 8.5) and in acidic soil known as Acidophiles. Basophiles - Agrophyron repens (Quack grass) Acidophiles -Cynodon dactylon Neutophiles-Digitaria sanguinalis 3. Biotic factors - the major effects on weeds are those exerted by the crop as it competes for available resources. the agricultural practices associated with the growing of a crop may encourage or discourage specific weeds. E.g., Ponding of water – Cynodon dies Repeated cultivation – discourages nutsedge. CROP-WEED INTERACTION Competition and allelopathy are the main interactions, which are of importance between crops and weeds. Allelopathy is distinguished from competition because it depends on a chemical compound being added to the environment.  10 Competition and allelopathy are the main interactions, which are of importance between crops and weeds. Competition involves removal or reduction of an essential factor or factors from the environment, which would have been otherwise utilized. I. Crop Weed Competition Weeds appear much more adapted to agro-ecosystems than our crop plants. Without interference by man, weeds would easily wipe out the crop plants. This is due to competition for nutrients, moisture, light and space, which are the principal factors of crop production. II. Competition for nutrients - Weeds usually absorb mineral nutrients faster than many crop plants and accumulate them in their tissues in relatively larger amounts. Amaranthus sp. accumulate over 3% N on dry weight basis and are termed as “nitrophills”. Achyranthus aspera, a ‘P’ accumulator with over 1.5% P2O5. Portulaca sp. are ‘K’ lovers with over 1.3% K2O in dry matter. Mineral Composition (%) of certain common Weeds on Dry Matter Basis No. Species N P2O5 K2O 1. Achyranthus aspera 2.21 1.63 1.32 2. Amaranthus viridis 3.16 0.06 4.51 3. Cynodon dactylon 1.72 0.25 1.75 4. Cyperus rotundus 2.17 0.26 2.73 Crop plants 1. Rice 1.13 0.34 1.10 2. Sugarcane 0.33 0.19 0.67 3. Wheat 1.33 0.59 1.44 2. Competition for moisture - Weeds transpire more water than do most of our crop plants. 3. Competition for light - It may commence very early in the season if dense weed growth smothers the crop seedlings. It becomes the most important element of crop-weed competition when moisture and nutrients are plentiful. In dry land agriculture, in years of normal rainfall the crop-weed competition is limited to nitrogen and light. Unlike competition for nutrients and moisture once weeds shade a crop plant, increased light intensity cannot benefit it. 4. Competition for space (CO2) - Crop-weed competition for space is the requirement for CO2 and the competition may occur under extremely crowded plant community condition. A more efficient utilization of CO2 by C4 type weeds may contribute to their rapid growth over C3 type of crops. A. Weed Competition on Crop Growth and Yield Crop growth and yield is affected.  11 Crop suffers from nutritional deficiency. Leaf area development is reduced. Yield attributes will be lowered. It reduces the water used by the crop and affects the dry matter production. It lowers the input response and causes yield reduction. Pest and disease incidence on crops will be more due to weeds. B. Factors affecting the Competitive Ability of Crops Against Weeds (a) Density of weeds - Increase in density of weeds decrease in yield is a normal phenomena. (b) Crop density - Increase in plant population decreases weed growth and reduces competition until they are self competitive. (c) Type of weeds species - The type of weeds that occur in a particular crop influences the competition. e.g., E. crusgalli in rice, R. exaltata in corn. (d) Type of crop species and their varieties - Crops and their varieties differ in their competing ability with weeds. Fast canopy forming and tall crops suffer less from weed competition than the slow growing and short statured crops. Dwarf and semi-dwarf varieties of crops are usually more susceptible to competition from weeds than the tall varieties. (e) Soil factor - Soil type, soil fertility, soil moisture and soil reaction influences the crop weed competition. Elevated soil fertility usually stimulates weeds more than the crop, thus reducing crop yields. Abnormal soil reactions often aggravate weed competition. (f) Climate - Adverse weather condition Favor weeds since most of our crop plants are susceptible to climatic stresses. All such stresses weaken crop capacity to fight weeds. (g) Time of germination - In general, when the time of germination of crop coincides with the emergence of first flush of weeds, it leads to intense Crop-Weed interference. Weed seeds germinate most readily from 1.25 cm of soil. Few weeds even from 15 cm depth. (h) Cropping practices - Cropping practices, have pronounced effects on Crop-Weed interference. (i) Crop maturity – As the age of the crop increases, the competition for weeds decreases due to its good establishment. Timely weeding in the early growth stages of the crop enhances the yield significantly. C. Critical period of Weed Competition Critical period of weed competition is defined as the shortest time span during crop growth when weeding results in highest economic returns. The critical period of crop-weed competition is the period from the time of sowing up to which the crop is to be maintained in a weed free environment to get the highest economical yield. Generally, in a crop of 100 days duration, the first 35 days after sowing should be maintained in a weed free condition. There is no need to attempt for a weed free condition throughout the life period of the crop.  12 Critical period of Weed Competition for important Crops No. Crops Days from flowering 1. Rice( upland) 35 2. Rice (Lowland) 60 3. Sorghum 30 4. Corn 30 5. Sugarcane 90 II. Allelopathy Allelopathy is the beneficial or harmful effects of chemicals or exudates produced by one (living) plant species to the environment and organisms around them On the germination, growth or development of another plant species (or even microorganisms) sharing the same habitat. FACTORS INFLUENCING ALLELOPATHY Plant factors Plant density: Higher the crop density the lesser will be reaction due to allelochemicals it. Life cycle: If weed emerges later there will be less problem of allelochemicals. Plant age: The release of allelochemicals occurs only at critical stage. Plant habitat: Cultivated soil has higher values of allelopathy than uncultivated soil. Climatic factors: The soil and air temperature as well as soil moisture influence the allelochemicals potential. Soil factors- chemical and biological properties influence the presence of allelochemicals. Stress factors- Abiotic and biotic stresses may also influence the activity of allelochemicals. Sour Orange Inhibit seed germination and root growth of pigweed, bermuda grass Mango Inhibit sprouting of purple nut sedge tubers. Jungle rice Inhibition of Rice Crabgrass Inhibition of Corn and Sunflower Sunn Hemp (Crotolaria sp.) Growth inhibition of lettuce and vegetable seed germination Leucaena Reduce yield of wheat and turmeric but increase yield of maize and rice Green spurge Inhibition of chickpea Jatropha curcas Inhibit corn and tobacco WEED CONTROL For designing any weed control program in a given area, one must know the nature and habitat of the weeds in that area, how they react to environmental changes and how they respond to herbicides. The primary objective of a weed management system is to maintain an environment that is as detrimental to weeds as possible by employing both preventive and curative measures either alone or in combination.  13 The principles of weed control are: Prevention Eradication Control Management A. Preventive Method It encompasses all measures taken to prevent the introduction and/or establishment and spread of weeds. No weed control program is successful if adequate preventive measures are not taken to reduce weed infestation. It is a long term planning so that the weeds could be controlled or managed more effectively and economically. Avoid using crop that are infested with weed seeds Avoid feeding screenings and other material containing weed seeds to the farm animals. Clean the farm machinery thoroughly before moving it from one field to another. This is particularly important for seed drills. Keep irrigation channels, fence-lines, bunds un-cropped areas and roads clean. Inspect your farm frequently for any strange looking weeds. Destroy such patches of a new weed by digging deep and burning the weed along with its roots. Quarantine regulations are available in almost all countries to deny the entry of weed seeds and other propagules into a country through airports and shipyards. B. Curative Methods 1. Eradication Measures - It is an ideal weed control method rarely achieved. It infers that a given weed species, its seed and vegetative part has been killed or completely removed from a given area Because of its difficulty and high cost, eradication is usually attempted only in smaller areas such as few ha., a few thousand m2 or less. Eradication is often used in high value areas This may be desirable and economical when the weed species is extremely noxious and persistent Weeds are destroyed immediately before its multiplication, dispersion and acclimatization as and when a new weed species is found. It can be done by, destroying the species at the initial stage of introduction and before it produces any propagule (at an early growth stage), and degenerating the buried dormant viable seeds by fumigation, flooding, heating and other methods. 2. Control Measures - In these method weeds growth is checked and the number of weeds (weed intensity) is minimized so that they do not affect crop yield. it encompasses processes whereby weed infestations are reduced but not necessarily eliminated. It is a matter of degree ranging from poor to excellent. WEED CONTROL aims at only putting down the weeds present by some kind of physical or chemical means  14 WEED MANAGEMENT is a system approach whereby whole land use planning is done in advance to minimize the very invasion of weeds in aggressive forms and give crop plants a strongly competitive advantage over the weeds. Weed control methods are grouped into 1. cultural 2. physical 3. biological 4. chemical A. MECHANICAL METHODS This method aims to destroy weeds by cutting and removing or by desiccation and exhaustion of weeds by several methods EXAMPLES: hand hoeing hand pulling tillage flooding burning mulching by non-living materials Hoeing - Hoe has been the most appropriate and widely used weeding tool for centuries. It is still a very useful implement to obtain results effectively and cheaply. It supplements the cultivator in row crops. Hand pulling/ hand weeding - It is done by physical removal or pulling out of weeds. It is the oldest method of controlling weeds. Digging - Digging is very useful in the case of perennial weeds to remove the underground propagating parts of weeds from the deeper layer of the soil. Tillage- includes plowing, harrowing and leveling which is used to promote the weed germination, which can be destroyed effectively later. In case of perennials, both top and underground growth is injured and destroyed by tillage. Burning - Burning or fire is often an economical and practical means of controlling weeds. Burning the weeds will control the weed problem in sugarcane, widely spaced field crops and orchards. Burning is used to dispose of vegetation destroy dry tops of weeds that have matured kill green weed growth in situations where other common methods are impracticable. Flooding - Flooding is successful against weed species sensitive to longer periods of submergence in water. The success of flooding depends upon complete submergence of weeds for longer periods. Mowing is a machine-operated practice mostly done on roadsides and in lawns. Sickling - Sickling is also done by hand with the help of sickle to remove the top growth of weeds to prevent seed production and to starve the underground parts. B. CULTURAL METHODS - Several cultural practices are employed for creating favorable condition for the crop. Cultural methods, alone cannot control weeds, They should, therefore, be used in combination with other methods.  15 Field preparation - The field has to be kept weed free. Flowering of weeds should not be allowed. Crop rotation - Can eliminate at least reduce difficult weed problems. The selected crops should grow thickly and develop dense canopy and shade to suppress the weeds. Growing of intercrops - Inter cropping suppresses weeds better than sole cropping Mulching - Mulch is a protective covering of material maintained on soil surface. Mulching has smothering effect on weed control by excluding light thus inhibiting the top growth. Summer tillage - The practice of summer tillage or off-season tillage is one of the effective cultural methods to check the growth of perennial weed population in crop cultivation. Optimum plant population - Lack of adequate plant population is prone to heavy weed infestation, which becomes, difficult to control later. Solarization - This is another method of utilization of solar energy for the desiccation of weeds. Blind tillage - The tillage of the soil after sowing a crop before the crop plants emerge. C. BIOLOGICAL METHODS - Biocontrol is defined as the use of living organisms to suppress a pest population, making it less abundant. Use of living organisms i.e., bioagents such as insects, disease organisms, herbivorous fish, snails or even competitive plants This method is not useful to control all types of weeds. Introduced weeds are best targets for biological control. C. CHEMICAL METHODS - Chemicals, which can kill the weeds or control weed growth are known as herbicides. INTEGRATED WEED MANAGEMENT Use of a judicial combination of mechanical, cultural, biological and chemical methods to achieve economic and effective weed control. IWM is the rational use of direct and indirect control methods to provide cost- effective weed control. Good IWM should be Flexible enough to incorporate innovations and practical experiences of local farmers. Developed for the whole farm Economically viable and practically feasible. Advantages of IWM It shifts the crop-weed competition in favor of crop Prevents weed shift towards perennial nature Prevents resistance in weeds to herbicides No danger of herbicide residue in soil or plant Suitable for high cropping intensity PESTICIDE CALCULATIONS Simple Conversion Factors  16 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 Calculations A. To calculate spray volume in liters per hectare, the information needed are : 1. size of sprayer (liters) 2. area of field (ha) 3. number of sprayer loads Formula: Liter of spray/ha = size of sprayer (liters) x no. of loads area of field (ha) Example: You have a 16-liter sprayer and you will apply 10 loads to a 0.5-ha field. What is your spray volume (liters/ha) in the field? Formula: liter of spray/ha = size of sprayer (liters) x no. of loads area of field (ha) Solution: Liter of spray/ha = 16 liters (size of sprayer) x 10 loads = 160 = = 320 liters 0.5 ha 0.5 B. To determine how many sprayer loads is needed to achieve a certain spray volume (liters/ha), use the equation: No. of loads = desired spray volume (liters/ha) x area of field(ha) size of sprayer (liters Example: You have a 16-liter sprayer, and wish to spray at a rate of 300 liters/ha in a 0.6-ha field. How many sprayer loads do you need to apply? Formula: No. of loads = desired spray volume (liters/ha) x area of field (ha) size of sprayer (liters) Solution: No. of loads = 300 ( desired spray volume in liters/ha) x 0.6 ha (area of field) 16 liters (size of sprayer) = 300 x 0.6 16 = 11.25 loads C. To calculate dosages needed for foliar sprays, convert rate recommendations to: percent concentration in the solution kg ai/ha  17 Calculations of % concentration in recommended solution. Rate recommendations on pesticide labels are often given in weight or volume of formulated product to be added to a certain weight or volume of water. Formula: Examples: 1. What is the % concentration of a spray solution if you add 5 tbsp of 70% WP of a product to 16 liters water? Solution: % concentration = 5 tbsp x 10 g/tbsp x 70% = 0.21% of the solution 16 liters x 1,000 ml/liter 2. What is the % concentration of a spray solution if you add 20 grams of 50% WP of product/5 gallons of water? Solution: % concentration = 20 g x 50% = 0.05% of the solution 5 gal x 3,800g/gal 3. What is the % concentration of a spray solution if you add 15 ml of 30% EC of product/ 20 liters of water? Solution: % concentration = 15 ml x 30% = 0.02% of the solution 20 liters x 1,000 ml/liter To calculate the rate of application when % concentration is known. The necessary information are: recommended rate (% concentration ai) volume (liters of spray desired/treated area) % a.i. in commercial formulation area (ha) to be treated You wish to apply 300 liters of spray solution/ha to a 0.5-ha area. The recommended spray concentration of the 50% EC fungicide is 0.04%. How many liters of the commercial formulations are required for the treatment? Solution: 1. Spray volume needed for the treated area = 300 liters x 0.5 ha = 150 liters 2. Liters of commercial formulation Volume of Spray x % Recommended Spray = Required Concentration % active ingredient in formulation = 150 x.04 = 0.12 liter 50 To calculate the rate of application when recommendations are based on kg a.i./ha. The necessary information are: recommended rate (kg a.i./ha) percent a.i. in the formulation area (ha) to be treated Example:  18 You wish to apply 350 liters/ha of spray solution to a 0.5-ha area. The recommended rate of the 70% wettable powder pesticide is 0.75 kg ai/ha. How many kilograms of the commercial formulation are required to treat the 0.5-ha area? Solution: recommended rate x area to be 1. Commercial = (kg a.i./ha) treated (ha) x 100 formulation (kg) % a.i. in commercial formulation = 0.75 x 0.5 x 100 = 0.536 70 2. Volume of spray needed = 350 liters/ha x 0.5 ha for the treated area = 175 liters 3. Amount of sprayer materials/sprayer load (kg) = kg of commercial x capacity of sprayer formulation (Liters) Amount of spray required (Liters) If you have a 16-liter sprayer: = 0.536 x 16 = 0.049 kg = 49 g/sprayer load 175 Note: Use the same equation for liquid formulations. Amounts will be in liters and milliliters and not kg and g. To apply pesticide granules, the necessary information are: recommended rate (kg a.i./ha) area to be treated (ha) percent a.i. in the granular formulation Example: You wish to apply pesticide granules at a rate of 0.5 kg ai/ha to a 2-ha field. The granules contain 3% ai. How many kilograms of commercial formulation are needed to treat this area? Solution: Recommended rate x area to be Commercial = (kg ai/ha) treated (ha) x 100 formulation (kg) % ai in commercial formulation = 0.5 x 2 x 100 = 33.33 kg 0.03 To calculate amount of chemical needed in bioassay, use the equation: ‘X” ppm = “Y” amount of chemical (g or ml) 1,000,000 “Z” (volume of water) Example: Determine the amount of chemical needed to dilute 500 ml water to attain the desired concentration of 300 ppm if the recommended rate of the fungicide is 3 tbsp/16 liters water. Solution: 300 = x = (300) x (500 ml) = 0.15 g or ml 1,000,000 500 ml 1,000,000 Problem Solving (Calculation) Determine the amount of a chemical (with 50% a.i.) needed to dilute 750 ml of water. The desired concentration is 0.2 %. Use the formula below. Amount of (Desired Concentration)(Volume of Water)  19 Chemical Needed = Active Ingredient (ACN) = 0.2 (750) 50 = 150 50 =3g 2. Determine the cost of the chemical needed Given = P 450 = 1000 ml or g of chemical 450:1000 = x: 3 1000 x = 3(450) = 1350 1000 Cost = P 1.35 CALIBRATION FOR KNAPSACK SPRAYER 1. check the sprayer to make sure there are no leaks, the nozzle is clear and the parts are in good condition. 2. stake out a test area in the field. 3. place a known amount of water into the sprayer tank. 4. establish the spray swath. 5. enter the test area and make the test run. 6. after spraying the test area, measure the length of the test area sprayed. 7. calculate the application rate in liters per hectare. Swath established (m) X distance traveled (m) Area Sprayed (ha) = ------------------------------------------------------------- 10,000 m2/ha Vol. sprayed (li) Application rate (li/ha) = ------------------------------- Area sprayed (ha) Appl’n rate (li/ha) No. of spray loads = -------------------------------------- Capacity of the sprayer R.R. (kg. a.i. per ha.) X Area (ha) Li./ Kg. per Ha = ------------------------------------------- % toxicant of the formulated product