Weed, Irrigation, and Insect Control in Vegetable Production (Week 7) PDF

Weed, Irrigation and controlling insects and diseases in vegetable production DR. WALEED AL-BUS AIDI Objectives To be familiar with weeds management in vegetable production To know the irrigation systems To identify the pest and disease control  Weeds Weeds are unwanted plants that grow in ar...

Weed, Irrigation and controlling insects and diseases in vegetable production DR. WALEED AL-BUS AIDI Objectives To be familiar with weeds management in vegetable production To know the irrigation systems To identify the pest and disease control  Weeds Weeds are unwanted plants that grow in areas where they compete with cultivated crops, gardens, or natural ecosystems and at the wrong time. Effective weed management starts with understanding weed growth habits and biology. Growers must identify specific weed problems for each crop type  Economic Losses Weeds lead to millions of dollars in losses due to: Lower crop yields Decreased produce quality Reduced operational efficiency Higher production costs Types of Weeds ◦ Broadleaf Weeds: Pigweed, purslane, common milkweed. ◦ Sedges: Yellow nutsedge. Grasses: Crabgrass, foxtails, barnyardgrass, wild proso millet. Weed Life Cycles Annuals: Complete life cycle in one year (e.g., barnyardgrass, giant foxtail), the most problematic for vegetables. ◦ Prevent Seed Production: Primary goal for controlling annual weeds Biennials: Two-year life cycle; control in first year to prevent seed production (e.g., wild carrot). Perennials: Live multiple years; harder to control due to extensive root systems (Canda thistle, johnosongrass). Start from seeds but spread mostly through asexual reproduction (rhizomes, stolons, tubers). Harder to control due to underground structures. Challenges in Managing Perennial Weeds Some die back to the ground in summar, making them difficult to detect. Control often requires both mechanical and chemical methods. ◦ Avoid using fields with heavy perennial weed infestations.  Weed Competition in Vegetable Production 1. Resource Competition Essential Resources: Weeds compete with crops for sunlight, carbon dioxide, water, nutrients, and space. Aggressive Growth: Weeds often dominate due to their rapid growth habits, especially during the first 4 weeks after crop emergence. 2. Critical Impact on Small-Seeded Crops Small-seeded crops like carrots and lettuce are highly susceptible to competition during early growth stages. 3. Pests and Diseases Insect Hosts: Weeds harbor pests that affect crops, such as: Carrot Weevil on wild carrots. Onion Thrips on ragweed and wild mustard. Disease Hosts: Weeds can be reservoirs for diseases that affect vegetables. 4. Allelopathy: A Form of Chemical Competition Definition: Some weeds release toxic or growth-inhibiting chemicals into the soil. ◦ Over 90 weed species exhibit allelopathic potential. Example: Common lambsquarter leachates inhibit tomato growth. Mechanical and culture control (Plowing) Importance: Increased reliance on nonchemical methods due to environmental and health concerns. Key Mechanical Methods Plowing: Effective primary tillage before planting to control small weeds and perennial weeds. ◦ Using Hiller plows for weed control in the garden Mechanical and culture control (Rotary Hoeing) Rotary Hoeing: Works well for large-seeded crops (e.g., sweet corn, beans, peas). Conduct after weed germination but before weed emergence. Rotary Hoe in Soybeans  Mechanical and culture control (Row Cultivation and Intertillage) 3. Row Cultivation and Intertillage: Most effective mechanical method for controlling weeds once crops are established. Intertillage: Traditional practice to manage weeds between crop rows. Mechanical and culture control (Hand Weeding and Hoeing) Hand Weeding and Hoeing: Effective for managing weeds directly within rows where they compete closely with crops. Limitations of Hand Weeding and Hoeing ◦ Labor-Intensive and Costly: High labor requirement makes these methods less feasible for large-scale, commercial vegetable production. Mechanical and culture control (Crop Rotation ) 1. Weed Management: Rotating vegetables with field crops (e.g., corn, soybeans, wheat) helps mitigate weed problems. 2. Preventing Weed Buildup through Rotation Strategy: Prevents the accumulation of common weeds (e.g., purslane) by diversifying crops planted in the same field. Use of Cover Crops: Barley, rye, sorghum, and alfalfa are highly competitive against weeds. Can be integrated into the rotation or used as fall cover crops. Mechanical and culture control (Mulching) Application of organic and synthetic materials to the soil surface to manage weeds. Weed Suppression through limit light penetration, preventing germination of weed seeds. Organic materials ◦ Hay (with or without newspaper under) ◦ Wood chips ◦ Straw ◦ Other Plastic ◦ Black ◦ Colored (silver, red, etc) ◦ Clear (not good for weed control) Mechanical and culture control (Other Nonchemical Strategies) 1. Avoiding Problematic Land Avoid planting vegetables in fields with a history of weed problems, particularly perennial weeds. 2. Selecting Competitive Crops Choose competitive crops like peas, potatoes, and cabbage. Avoid less competitive vegetables such as onions and carrots. 3. Growers Should Use Cultivars Adapted to Local Conditions Use cultivars that are well-adapted to the local area for better resilience. 4. Balanced Crop Fertility, Integrated Pest and Diseases Management: Maintain balanced soil fertility to support healthy crop growth. Implement effective insect and disease management practices.  Chemical Control in Weed Management Historical Start: Began with 2,4-D in 1944, an auxin-type plant growth regulator. ◦ Labor and Time Savings: ◦ Chemical methods are less time-consuming compared to mechanical and cultural practices. ◦ Reduced Energy Expenditure: ◦ Requires less physical and mechanical energy than nonchemical approaches. Chemical Control in Weed Management Efficiency: ◦ Reduces time and labor compared to mechanical and cultural methods. ◦ Control of Perennial Weeds: Effective for difficult-to-manage perennial weeds, especially in areas unsuitable for cultivation. ◦ Can be used on Non-Cultivatable Areas: Herbicides enable the use of previously weedy land for vegetable production Targeted Weed Control Based on Crop Type: ◦ Between Rows: Managed with cultivation. ◦ Within Rows: Herbicides selectively control weeds.  Chemical Control in Weed Management Types of Herbicides ◦ Selective Herbicides: Target specific weed groups without harming the crop. Example: 2,4-D controls broadleaf weeds in sweet corn without affecting grasses. ◦ Nonselective Herbicides: Kill most vegetation types (e.g., paraquat). Chemical Control in Weed Management Herbicide Classification ◦ By Chemical Structure: e.g., Triazines, Dinitroanilines, Acetanilides. ◦ By Mode of Action: Targets plant functions, such as: ◦ Photosynthesis Inhibition ◦ Meristem Inhibition ◦ Amino Acid Synthesis Inhibition Application Types: Systemic Herbicides: Absorbed and moved to specific plant parts. Contact Herbicides: Act on vegetative areas they directly contact. Herbicide Selection Criteria ◦ Considerations: Crop species, soil type, climate, weed type. ◦ Site-Specific Selection: Weed identification and site history help optimize herbicide choice. Chemical Control in Weed Management Types of Herbicide Applications ◦ Preplant (PPI): Applied before planting; worked into the soil to reach weed root zones. ◦ Preemergent (PRE): Applied after planting but before crop and weed emergence. Requires moisture (rain/irrigation) for activation. ◦ Postemergent: Applied after crop emergence; often more effective under high temperature and humidity. Application Methods ◦ Broadcast Treatments: Uniform application across the entire field. ◦ Foliar Treatments: Targeted to weed leaves for direct absorption. ◦ Band Treatments: Narrow strip application over crops with mechanical control in aisles. ◦ Directed Sprays: Targeted on specific plant areas, protecting crop areas sensitive to herbicide. Application Forms: ◦ Granules or sprays, with sprays generally allowing better precision. Irrigation in Vegetable Production Irrigation is crucial to maintain steady water availability where nearly all crops are irrigated.  Water Requirements in Vegetable Production High Consumption: Some crops require 400-600 pounds of water per pound of dry matter. Examples (San Joaquin Valley, CA): Lettuce: 23 gallons per pound Carrots: 33 gallons per pound Spinach: 61 gallons per pound Sweet Corn: 122 gallons per pound Influencing Factors ◦ Natural Factors: Soil type, topography, climate (e.g., temperature, solar radiation, wind). ◦ Management Factors: Irrigation scheduling, water quality, planting date, crop type, and pest control. Frequency and Amount in Vegetable Irrigation) Rate of Water Use: Affected by: Crop Growth Stage: Younger plants use less water. Weather Conditions: Temperature, humidity, wind, and evapotranspiration. General Water Requirements ◦ Humid Regions: Typically 2.5 to 5 cm per week during the growing season. ◦ Hot, Dry, Windy Conditions: May require 7.6 to 10 cm per week. ◦ Arid Regions: Up to 10 cm per week needed for optimal growth. Seasonal Water Use Dynamics ◦ Early Season: Young plants have a limited root system and lower water use. ◦ Later Season: Increased crop canopy size leads to higher transpiration rates. Greater rooting depth allows for less frequent irrigation. Light, Frequent Irrigations: Generally not recommended except for seedlings. Less Frequent, Deeper Irrigations: Ideal for mature crops to promote deep rooting and reduce water wastage. Irrigation Methods: Surface Irrigation Surface Irrigation ◦ Water is spread over the surface of the land. Common Systems: Flood Irrigation ◦ Advantages: ◦ Effective for leaching salts from the surface into the subsoil. ◦ Well-suited for flat fields with adequate drainage. Furrow Irrigation ◦ Advantages: ◦ Reduces water runoff and improves water distribution to crops. Surge Irrigation (modification of furrow irrigation) ◦ Advantage: ◦ Promotes uniform water application from the beginning to the end of the furrow. Surface Irrigation Disadvantages: Requires constant attention and management to ensure proper water distribution. ◦ Soil Issues: Tendency for soil to crust, which can affect water infiltration. ◦ Water Loss: Significant water loss through seepage in supply ditches, potentially reducing efficiency. Sprinkler Systems: Traveling Guns and Other Traveling Guns Portable Pipe Solid-Set Pipe Wheel-Roll Systems Trickle (Drip) Irrigation Operates under low pressure (6-20 psi) with point-source and slow application. High efficiency due to precise water delivery at the root zone. Emitters: Regulate the rate and amount of water, releasing it slowly for better infiltration. Trickle (Drip) Irrigation Advantages: Water Efficiency: Matches infiltration rate, minimizing runoff and water waste. Fertilizer/Pesticide Integration: Fertilizers or pest control products can be applied through the system. Reduced Plant Wetting: Minimizes wetting of plant foliage, lowering disease risks. Automation Potential: Compatible with automated control systems. Coordination with Pest Control: Allows easy synchronization of irrigation and foliar pest control schedules.  Trickle (Drip) Irrigation Disadvantages ◦ Clogging: Emitters may clog from debris, algae, or fungal growth. ◦ Salt Buildup: Salt may accumulate around the perimeter of the wetting area in arid climates. ◦ Higher Cost: Installation and material costs are higher than conventional systems.  Subirrigation System Requirements ◦ Soil Type: ◦ Sandy loam topsoil for effective water movement. ◦ Impervious subsoil to retain water and prevent deep drainage. ◦ Water Supply: ◦ Requires an abundant water source to maintain soil moisture levels. ◦ Drainage: ◦ Good drainage is essential to prevent waterlogging. Subirrigation Advantages ◦ Undisturbed Soil Mulch: Reduces surface disturbances, maintaining a natural mulch layer that helps conserve soil moisture. ◦ Prevents Soil Baking: Reduces crusting or compaction of the soil surface, supporting better root growth and air exchange. Disadvantages ◦ High Water Demand: Requires a substantial water supply, which can limit its use in areas with limited water resources. ◦ High Installation Cost: Often involves the installation of tile piping or similar infrastructure, making initial costs significant. ◦ Complex Feasibility: Soil and water supply suitability must be carefully evaluated to ensure the system’s effectiveness. Water Quality in Irrigation for Vegetable Crops 1. Determinants of Water Quality is Concentration of dissolved salts in irrigation water. Effect on Soil: Increased salinity affects soil osmotic pressure, making water uptake challenging for plants. 2. Impact of High Salinity on Plants Reduced Water Absorption: High salt levels hinder root water uptake. Symptoms: Similar to drought stress, causing wilting and impaired growth. 3. Crop Sensitivity to Salinity High Sensitivity: Beans, carrots, and onions suffer yield loss under high salinity. Salt-Tolerant Crops: Asparagus, beets, and spinach can thrive in saline conditions.  Toxic Elements in Irrigation Water 1. Common Toxic Elements in Natural Waters Key Elements: Chloride, Sodium, and Boron Effect: Can become toxic to plants, affecting growth and yield 2. Crop Sensitivity to Specific Elements High Sensitivity: Beans, onions, Jerusalem artichokes – Sensitive to boron (>1 ppm) causing yield reductions Burn from Sodium & Chloride – Occurs with sprinkler irrigation in low humidity, high evaporation Tolerance: Asparagus and beets are more boron-tolerant 3. Water Quality Standards for Vegetables (Ideal Levels) Salinity: < 480 ppm (total dissolved solids) Sodium (SAR): < 3.0 Boron: < 1 ppm Chloride: < 100 ppm 4. Additional Water Quality Components Bicarbonate: Impacts soil permeability Nitrate and pH: Also important for soil and plant health Calcium Carbonate Deposits: Aesthetic issue with sprinkler systems, especially in areas with high bicarbonate Pest Control in Vegetable Production Reduced Yields: Directly lowers the volume of marketable produce Quality Decrease: Affects appearance, texture, and taste Increased Costs: More resources spent on production and harvesting Higher Expenditures: Costly equipment and materials for pest control measures Financial Impact on Growers Income Loss: Reduced quality and yields lower profitability Crop Loss Risk: Severe infestations can result in total crop failure Controlling Insects in Vegetable Crops Types of Insect Pests 1.Beetles: Bore holes in foliage 2.Caterpillars & Worms: Feed on foliage, sometimes on fruits 3.Cutworms, Earworms & Borers: Tunnel into corn ear tips and fruits 4.Soil Maggots, Grubs & Wireworms: Target seeds and plant roots 5.Aphids, Whiteflies, Scale & Mites: Suck juices from new foliage 6.Plant Bugs (adults & immatures): Suck juices from foliage and fruits Effective Insect Management ◦ Identification: Accurate identification of pest types ◦ Understanding Biology & Habits: Knowing life cycle and feeding behavior aids control ◦ Targeted Control Methods: Tailored to pest types and plant vulnerabilities  Scouting for Insect Pests Importance of Scouting ◦ Essential for early detection of insect pests ◦ Helps implement control measures before infestations worsen ◦ Reduces potential crop damage and loss Scouting Techniques ◦ Visual Inspection: Check for signs of infestation (e.g., eggs, frass, damaged leaves/fruit) ◦ Monitoring Tools: Use light traps and pheromone traps to assess pest populations (e.g., corn borers, earworms) ◦ Benefits of Scouting ◦ Provides critical information on: Extent of pest presence Development stages of insects ◦ Saves time and resources by enabling timely interventions Categories of Insecticides 1.Inorganic Compounds: 1. Examples: Cryolite, various types of sulfur 2. Usage: Less common in vegetable production 2.Organic Compounds: 1. Botanical Insecticides: Derived from plants (e.g., pyrethrum, rotenone) 2. Synthetic Organic Chemicals: 1. Chlorinated hydrocarbons 2. Organic phosphates 3. Carbamates 4. Pyrethroids Types of Formulations 1.Emulsifiable Concentrates (EC): 1. Description: Concentrates that mix with water to form an emulsion. 2. Application: Sprayed with hand or power equipment. 2.Flowable Concentrates (FC): 1. Description: Similar to emulsifiable concentrates but often contain suspended solids. 2. Application: Requires dilution with water before spraying. 3.Wettable Powders (WP): 1. Description: Powders that mix with water to form a suspension. 2. Application: Sprayed after dilution. 4.Granular Insecticides: 1. Description: Small clay pellets impregnated with insecticide. 2. Usage: Primarily for soil insects; can be applied by aircraft or specialized equipment. 5.Dusts: 1. Description: Ready-to-use formulations; not commonly used commercially. 2. Usage: Typically applied by home gardeners using hand or power dusters. Biological Control: Microbial Insecticides Microbial Insecticides: Definition: Control of insects using microorganisms. Example: Bacillus thuringiensis (Bt): A bacterium that produces toxins effective against over 400 species of leaf-feeding caterpillars. Available in liquid concentrate or wettable powder forms for spraying on infested plants. Advantages: Selective Control: Does not harm insect predators and parasites. Residue-Free: No harmful chemical residues on produce at harvest. Usage: Effective for home gardeners and commercial growers; ideal for leaf- and fruit-eating caterpillars. Controlling Diseases in Vegetable Production Preventive Approach: Disease control measures must start before disease symptoms appear in the field. Involves soil sterilization and seed treatment. Use of Fungicides: Applied to growing plants to kill or control plant diseases. Most vegetable diseases can now be prevented with timely fungicide applications. If diseases occur, fungicides can sometimes reduce severity, although not all may be effective once a disease is established. Soil Sterilization and Seed Treatment Purpose of Soil Sterilization: Eliminate fungi, bacterial spores, insect pupae, and weed seeds. Methods: Chemical: Formaldehyde drench, Chloropicrin (tear gas). Physical: Boiling water dip, Steam heating (most practical in steam-heated greenhouses). Importance of Seed Treatment: Controls seed-borne diseases, especially when soil sterilization isn't feasible. Seeds can be pre-treated commercially or treated by growers using materials like Captan and Thiram. Hot-water treatment is effective but requires careful control of time and temperature. Fungicides for Disease Prevention Post-Transplant Disease Prevention: Consideration of fungicides after seedlings are transplanted or sprouted. Application Techniques: Dipping seedlings (e.g., cabbage, pepper) in fungicide solution before transplanting. New automatic seedling transplanting machines can mix fungicide with water during transplanting. Timing for Application: Best results when applied before signs of plant damage, protecting susceptible plants from pathogens. Some newer fungicides allow delayed application until symptoms appear without major crop impact. For crops where cosmetic quality is crucial (e.g., celery, lettuce), early application is essential. Application Methods for Fungicides Forms of Application: Sprays: Preferred method for better adherence and longer-lasting protection. Effective even in mild breezes. Dusts: Can only be applied in calm conditions (little or no wind). Application Frequency: Based on the recommendation Nematodes in Vegetable Crops Nematodes are small eelworms (< 1/16 inch) that can injure all vegetable crops. Damage varies by crop, soil type, and cropping history. Root Knot Nematode: Common type causing distinct galls on roots (size: pinhead to 1 inch). Affects cabbage and other crucifers. Lifecycle: Nematodes live in soil and decaying vegetable material, feeding on plant roots. Damage is often underestimated by growers and researchers. Control Methods: Crop Rotation: Incorporate nematode-resistant cultivars. Soil Fumigation: Expensive and requires skilled applicators. Many fumigants are no longer available due to regulations. Applied several inches deep to kill nematodes; soil must rest before planting. Combining Insecticides and Fungicides Simultaneous Application: Insecticides and fungicides can be applied together when disease and insect problems coincide. Chemical Compatibility: Ensure both products are chemically compatible to avoid issues. Incompatible mixtures may lead to: Reduced effectiveness against insects and diseases. Chemical breakdown of compounds in the spray tank. Consult Compatibility Charts: Growers should refer to compatibility charts for guidance. Charts indicate which materials can or cannot be mixed together. Compatibility information is often available from state extension specialists. Safe Handling of Insecticides and Fungicides Toxicity Awareness: All insecticides and fungicides are toxic to humans and animals. Risks are highest for spray tank mixers and applicators. Routes of Exposure: Ingestion: Swallowing pesticide concentrates. Inhalation: Breathing in dust or vapors. Dermal: Skin absorption from spills or spray. Child Safety: Children are frequent victims of accidental poisoning. Keep all pesticides in original containers and locked up, or out of reach of children. General Safety Rules for Applicators Read and follow label warnings and directions carefully. Wear rubber gloves when handling concentrates. Wash hands before eating or smoking. Remove and wash contaminated clothing immediately. Shower and change clothes at the end of the workday. Conduct operations in well-ventilated areas. Store unused pesticides in original containers with labels intact. Dispose of empty containers safely and according to regulations. Keep pesticides out of reach of children and animals. Avoid applying during weather conditions that favor drift or near wells.