Pesticides Classification, Use, and Management Study Guide

Fundamentals of Pesticides

  • Definition: A pesticide is defined as any substance or mixture of substances intended to prevent, destroy, repel, or mitigate any pest that causes damage to crops.

  • Presenter / Author Context: Prepared by Geraldine L. Acdal, RAgr.

  • Four Core Functional Actions:

    • Prevent: Keeps pests from attacking crops by creating a protective barrier or environmental condition that prevents pest infestation before it occurs.

    • Destroy: Kills pests that damage crops, eliminating them directly through chemical action.

    • Repel: Keeps pests away from crops by discouraging them from approaching, alighting on, or feeding on plant parts.

    • Mitigate: Reduces the severity of pest damage, minimizing pest impact and assisting crops to recover and remain productive.

  • Target Pest Scope: Encompasses insects, plant pathogenic fungi, rodents, weeds, nematodes, plant pathogenic bacteria, and snails/slugs.

Advantages and Disadvantages of Pesticide Use

  • Advantages of Pesticides:

    • Protect Crop Yield: Effectively controls destructive pests and diseases, guaranteeing higher and more stable agricultural yields.

    • Improve Crop Quality: Produces healthier, uniform, and highly marketable crops featuring superior visual appearance and economic value.

    • Prevent Disease Outbreaks: Halts the spread of infectious pests and pathogens, safeguarding crop populations and preventing severe, large-scale disease epidemics.

    • Reduce Economic Losses: Minimizes crop losses and physical damage, lowering overall operational costs while increasing net profit margins for agricultural producers.

    • Increase Food Production: Enhances global food supply to keep pace with rapid population growth and fortify long-term food security.

  • Disadvantages of Pesticides:

    • Environmental Pollution: Contaminates soil, groundwater, surface water, and ambient air, damaging delicate ecosystems and inflicting long-term ecological harm.

    • Human Toxicity: Triggers acute and chronic health complications in human populations, including chemical poisoning, oncogenesis (cancer), endocrine/hormonal disruption, and neurological deficits.

    • Resistance Development: Accelerates biological evolution in target pests, rendering chemicals progressively less effective over time through selection pressure.

    • Residue Problems: Chemical residues persist in harvested food products and potable water, creating significant health risks for consumers when exceeding established maximum residue limits.

    • Death of Beneficial Organisms: Kills non-target beneficial species, including plant pollinators (e.g., bees), natural insect predators, parasites, and vital soil microorganisms required for ecological balance.

Primary Classifications According to Target Pest

  • Insecticide: Targets and controls insect pests.

  • Fungicide: Targets and controls plant pathogenic fungi.

  • Herbicide: Targets and controls unwanted vegetation and weeds.

  • Nematicide: Targets and controls plant-parasitic nematodes.

  • Bactericide: Targets and controls plant pathogenic bacteria.

  • Rodenticide: Targets and controls rats and mice.

  • Molluscicide: Targets and controls snails and slugs.

  • Acaricide: Targets and controls plant-feeding mites and ticks.

  • Algicide: Targets and controls algae growth in water bodies.

Exhaustive Breakdown of Target Categories and Chemical Agents

  • Insecticides:

    • Primary Target Insects: Stem borers, aphids, leafhoppers, armyworms, thrips, and whiteflies.

  • Fungicides:

    • Primary Fungal Diseases Controlled: Rice blast, downy mildew, anthracnose, powdery mildew, leaf spot, and rust.

  • Herbicides:

    • Application Timing Classifications:

    • Pre-emergence: Applied to the soil prior to weed seed germination; forms a chemical barrier that stops seeds from sprouting.

    • Post-emergence: Applied directly to weeds after they have emerged above the soil surface; absorbed via foliage or stems and translocated throughout the plant.

    • Selectivity Classifications:

    • Selective: Selectively destroys target weed species without causing harm to crop plants when applied according to directions (Example crops: corn, rice, wheat, soybeans; Example chemicals: 2,4-D, atrazine, metolachlor).

    • Non-selective: Destroys all or most vegetation contact points; utilized in non-crop areas or prior to crop planting (Example uses: field clearing, fence rows, path maintenance, seedbed preparation; Example chemicals: glyphosate, paraquat).

    • Representative Herbicide Active Ingredients:

    1. Glyphosate (41% SL): Non-selective, post-emergence herbicide. Foliar spray application absorbed through leaves. Controls broadleaf weeds, grasses, and sedges.

    2. 2,4-D (72% SL): Selective, post-emergence herbicide. Foliar spray application absorbed through leaves. Controls broadleaf weeds (e.g., ipil-ipil, amaranth, dandelion).

    3. Butachlor (60% EC): Selective, pre-emergence herbicide. Soil application preventing weed seed germination. Controls annual grasses and select broadleaf weeds.

    4. Pendimethalin (30% EC): Selective, pre-emergence herbicide. Soil application preventing weed seed germination. Controls annual grasses and broadleaf weeds.

  • Bactericides:

    • Representative Bactericide Active Ingredients:

    1. Copper Hydroxide (50% WP): Dual Fungicide/Bactericide. Chemical formula: Cu(OH)2Cu(OH)_2. Mode of Action: Contact bactericide that disrupts bacterial cell enzymes and proteins. Controls bacterial leaf spot, citrus canker, and bacterial leaf blight of rice.

    2. Copper Sulfate (98% WP): Chemical formula: CuSO4⋅5H2OCuSO_4 \cdot 5H_2O. Mode of Action: Contact bactericide that denatures structural proteins and damages cell membranes. Controls bacterial leaf blight of rice, bacterial wilt, and citrus canker.

    3. Kasugamycin (2% SL): Chemical Class: Aminoglycoside antibiotic. Mode of Action: Systemic bactericide that inhibits bacterial protein synthesis by binding to the 30S30S ribosomal subunit. Controls bacterial leaf blight of rice, bacterial wilt, and bacterial soft rot.

    4. Oxolinic Acid (20% WP): Chemical Class: Quinolone. Mode of Action: Systemic bactericide that inhibits bacterial DNA gyrase and blocks cell division. Controls bacterial leaf blight of rice, citrus canker, and bacterial wilt.

  • Nematicides:

    • Representative Nematicide Active Ingredients:

    1. Fluopyram (400 SC): Chemical Class: SDHI (Succinate Dehydrogenase Inhibitor). Mode of Action: Disrupts mitochondrial energy production in nematodes.

    2. Oxamyl (240 SL): Chemical Class: Carbamate. Mode of Action: Inhibits acetylcholinesterase in nematode nervous systems.

    3. Fosthiazate (10 G): Chemical Class: Organophosphate. Mode of Action: Inhibits acetylcholinesterase in nematode nervous systems.

    4. Abamectin (18 EC): Chemical Class: Avermectin. Mode of Action: Activates glutamate-gated chloride channels, causing paralysis and death.

    • Target Nematode Groups: Root-knot nematodes, cyst nematodes, and lesion nematodes.

  • Rodenticides:

    • Function & Application: Formulated into palatable baits to reduce rodent populations and protect crops and infrastructure.

    • Target Species: Rats and mice.

    • Common Active Ingredients: Bromadiolone, Brodifacoum, Difethialone, Diphacinone.

    • Safety Protocol: Must be deployed in tamper-resistant bait stations to prevent non-target animal and human exposure.

  • Molluscicides:

    • Target Pests: Snails (e.g., Golden apple snail) and slugs (e.g., Deroceras spp.).

    • Plant Damage Symptoms: Leaf perforation holes, chewed young seedlings, damaged fruit surfaces, and yield loss.

    • Application Methods:

    • Broadcasting: Even distribution of pellets across target fields during early morning or late afternoon when pest activity peaks.

    • Baiting: Placement of bait pellets inside protective stations/containers.

    • Spraying: Liquid formulation spraying targeted precisely at active pest feeding zones.

    • Representative Molluscicide Formulations:

    1. Metaldehyde: Pellet formulation. Attractant mode of action; disrupts mucosal slime secretion, causing fatal dehydration.

    2. Iron Phosphate: Pellet formulation. Ingestion stops pest feeding activity, resulting in die-off.

    3. Niclosamide: Pellet formulation. Disrupts pest nervous system function.

    4. Copper Sulfate: Liquid/solution formulation. Direct molluscicide toxicity; causes membrane cellular disruption and dehydration.

    • Safety Precautions: Wear protective gloves, avoid inhalation and skin contact, wash hands after application, avoid eating/drinking/smoking during use.

    • Integrated Management Practices: Combine chemical application with cultural sanitation, biological predators (e.g., ducks), and physical barriers (e.g., copper tape).

  • Acaricides:

    • Target Mites: Plant-parasitic mites such as the Red Spider Mite (Tetranychus spp.) and Broad Mite (Polyphagotarsonemus latus), along with various tick species.

    • Damage Symptoms: Foliar stippling/speckling, leaf bronzing and scorching, webbing, and growth distortion.

    • Host Crops: Tomato, pepper, eggplant, cucumber, ornamentals, and mango.

    • Life Cycle Dynamics: Egg →\rightarrow Larva →\rightarrow Nymph →\rightarrow Adult (7–147\text{--}14 days total cycle duration depending on temperature and species).

    • Acaricide Active Ingredients, Groups, and Actions:

    • Abamectin (Avermectin group): Disrupts nerve signal transmission, causing paralysis and death.

    • Bifenazate (Diazine group): Specific miticide targeting development.

    • Hexythiazox (Thiazolidine group): Inhibits egg growth and nymphal molting.

    • Spirodiclofen (Tetronic acid derivative group): Inhibits lipid synthesis.

    • Fenpyroximate (Pyrazole group): Inhibits mitochondrial electron transport.

    • Propargite (Sulfite ester group): Inhibits ATP synthase.

    • Application Guidelines: Apply early during initial infestation; target undersides of leaves thoroughly; rotate active ingredient groups (modes of action) to delay resistance; wear complete Personal Protective Equipment (PPE) including gloves, mask, goggles, and long sleeves.

  • Algicides:

    • Target Algal Groups: Simple photosynthetic organisms including Green algae (Chlorella sp.), Filamentous algae (Cladophora sp.), Blue-green algae (Cyanobacteria), and Diatoms.

    • Negative Impacts of Excessive Algae: Decreases dissolved oxygen concentration causing fish kills, clogs irrigation tubing, releases biological toxins, restricts water flow velocity, damages crop and aquaculture production, and impairs water quality.

    • Algicide Active Ingredients & Applications:

    1. Copper Sulfate (CuSO4⋅5H2OCuSO_4 \cdot 5H_2O) (Inorganic copper compound): Releases free copper ions disrupting enzyme systems and metabolic functions. Used in ponds, canals, ornamental waters, and irrigation networks.

    2. Copper Hydroxide (Inorganic copper compound): Interferes with cellular metabolism. Used in fish ponds, natural lakes, and reservoirs.

    3. Sodium Hypochlorite (Oxidizing agent): Oxidizes cell structural components. Used in drinking water reservoirs, holding tanks, and pools.

    4. Diquat (Quaternary ammonium compound): Accepts electrons from photosystem I, halting photosynthesis. Used in irrigation canals and flooded rice fields.

    5. Hydrogen Peroxide (Oxidizing agent): Generates destructive hydroxyl free radicals. Used in open aquaculture systems and ornamental waters.

    6. Glutaraldehyde (Aldehyde compound): Cross-links structural proteins and disrupts membrane integrity. Used in industrial water systems and cooling towers.

    • Application Strategies: Spot treatment, surface spraying, tank/reservoir treatment, and systemic application through irrigation systems.

    • Disposal Protocol: Do not reuse pesticide containers; perform a triple-rinse process on empty containers, puncture them physically, and dispose of them according to local hazardous waste regulations.

Classification According to Mode of Action

  • Contact Pesticides:

    • Physical Behavior: Remain exclusively on the external surfaces of plant foliage and stems; do not penetrate or translocate through plant vascular systems.

    • Biological Action: Kills target pests through direct physical contact. Provides local protection restricted strictly to treated plant tissue surfaces.

    • Representative Examples: Mancozeb (Mancozeb 75% WP fungicide), Copper fungicides (Copper Oxychloride 50% WP fungicide).

  • Systemic Pesticides:

    • Physical Behavior: Absorbed directly into plant tissues and translocated internally via the vascular transport networks (xylem and/or phloem).

    • Biological Action: Travels to untreated tissue and new foliage shoots, offering internal systemic protection against feeding pests across the entire plant body.

    • Representative Examples: Propiconazole (250 EC fungicide), Metalaxyl (35 WP fungicide), Imidacloprid (200 SL insecticide).

Classification According to Chemical Group

  • Fungicide Chemical Classes:

    1. Dithiocarbamates: Multi-site contact protectant fungicides. Examples: Mancozeb, Maneb, Zineb, Thiram. Targets: Leaf spots, blights, downy mildew, anthracnose.

    2. Triazoles: Systemic fungicides that inhibit ergosterol biosynthesis in fungal membranes. Examples: Propiconazole, Tebuconazole, Difenoconazole, Hexaconazole. Targets: Powdery mildew, leaf spots, rust, anthracnose.

    3. Strobilurins: Systemic QoI fungicides that inhibit mitochondrial respiration. Examples: Azoxystrobin, Kresoxim-methyl, Pyraclostrobin, Trifloxystrobin. Targets: Rust, leaf spots, powdery mildew, Botrytis.

    4. Benzimidazoles: Systemic fungicides that inhibit cell division and tubulin assembly. Examples: Carbendazim, Benomyl, Thiophanate-methyl. Targets: Anthracnose, root rots, leaf spots, damping-off.

    5. Phenylamides: Systemic fungicides with acylation activity on RNA polymerase target sites. Examples: Metalaxyl, Mefenoxam, Dimethomorph, Benalaxyl. Targets: Downy mildew, late blight, root rots, damping-off.

    6. Copper Compounds: Multi-site contact protectant fungicides. Examples: Copper hydroxide, Copper oxychloride, Bordeaux mixture, Copper sulfate. Targets: Bacterial blight, leaf spots, downy mildew, canker diseases.

  • Insecticide Chemical Classes:

    1. Pyrethroids: Synthetic analogs of natural pyrethrins. Alter voltage-gated sodium channels in nerve axons, inducing rapid pest knockdown. Mode of action: Contact and stomach action. Examples: Cypermethrin, Lambda-cyhalothrin, Deltamethrin, Permethrin. Targets: Caterpillars, aphids, thrips, mosquitoes.

    2. Neonicotinoids: Systemic insecticides acting agnostically on nicotinic acetylcholine receptors (nAChR), causing nerve excitation, paralysis, and death. Mode of action: Systemic action. Examples: Imidacloprid, Thiamethoxam, Clothianidin, Acetamiprid. Targets: Aphids, whiteflies, leafhoppers, termites.

    3. Organophosphates: Irreversibly inhibit acetylcholinesterase (AChE), leading to extreme acetylcholine accumulation, continuous nerve firing, paralysis, and death. Mode of action: Contact and stomach action. Examples: Chlorpyrifos, Dimethoate, Malathion, Parathion. Targets: Borers, aphids, beetles, leafminers.

    4. Carbamates: Reversibly inhibit acetylcholinesterase (AChE); feature lower environmental persistence than organophosphates. Mode of action: Contact and stomach action. Examples: Carbaryl, Methomyl, Propoxur, Aldicarb. Targets: Caterpillars, beetles, aphids, leafhoppers.

    5. Diamides: Activate intracellular ryanodine receptors in muscle cells, stimulating uncontrolled calcium release, persistent muscle contraction, feeding cessation, and death. Mode of action: Stomach action via ingestion. Examples: Chlorantraniliprole, Flubendiamide, Cyantraniliprole. Targets: Caterpillars, fruit borers, leafminers, armyworms.

Classification According to Formulation

  • Dust (D): Finely ground active ingredient blended with inert dry carriers, applied in dry powder form (Example: Sulfur Dust).

  • Wettable Powder (WP): Dry powder formulation containing wetting agents that disperses in water to form a temporary suspension upon mechanical agitation (Example: Mancozeb WP).

  • Water Dispersible Granules (WDG): Granular formulation that breaks down rapidly upon addition to water, forming a sprayable suspension (Example: Thiamethoxam WDG).

  • Granules (G): Large dry particles designed specifically for direct dry soil application without water dilution (Example: Carbofuran G).

  • Soluble Powder (SP): Dry powder formulation that dissolves completely in water to produce a true, clear solution (Example: Metalaxyl SP).

  • Suspension Concentrate (SC): Stable liquid suspension containing solid active ingredient particles suspended in a liquid medium (Example: Chlorantraniliprole SC).

  • Emulsifiable Concentrate (EC): Liquid formulation containing oil-soluble active ingredients and emulsifiers that form an emulsion (oil droplets dispersed in water) when combined with water (Example: Lambda-cyhalothrin EC).

  • Ultra-Low Volume (ULV): Extremely concentrated liquid active formulation applied without water dilution using specialized ULV machinery or aerial sprayers (Example: Malathion ULV).

Reading Pesticide Labels, Toxicity Categories, and Safe Handling

  • Ten Essential Components of a Pesticide Label:

    1. Trade Name: The commercial brand name of the product (e.g., GREENSHIELD® 250 SC).

    2. Common Name: The standardized generic name of the active chemical ingredient (e.g., Carbendazim).

    3. Active Ingredient: The specific chemical component providing pesticidal activity (e.g., Carbendazim 250 g/L250\,g/L; Inert Ingredients 750 g/L750\,g/L; Total 1000 g/L1000\,g/L).

    4. Target Pest: Specific pest species or plant diseases approved for treatment (e.g., Rice Blast - Magnaporthe oryzae, Leaf Spot, Sheath Blight).

    5. Application Rate: Dosage instructions per volume (e.g., 20–30 mL20\text{--}30\,mL diluted in 16 L16\,L of water per knapsack sprayer).

    6. Safety Precautions: Directive warnings detailing exposure risks and handling safety protocols.

    7. Signal Word: Standardized text highlighting acute toxicological risk levels.

    8. Pre-Harvest Interval (PHI): The mandatory minimum interval (in days) required between the final pesticide application and crop harvest (e.g., 14 days).

    9. Re-Entry Interval (REI): The mandatory minimum time frame (in hours) before farm workers can safely enter treated fields without personal protective equipment (e.g., 24 hours).

    10. Expiry Date: Guarantee deadline date for active product stability and efficacy (e.g., 31 December 2026).

  • Toxicity Signal Words & Toxicity Ratings:

    • DANGER - POISON (Extremely Toxic): Potentially fatal if ingested, inhaled, or absorbed through skin tissue.

    • DANGER (Highly Toxic): Severe exposure causes permanent injury, tissue damage, or severe illness.

    • WARNING (Moderately Toxic): Exposure induces temporary physical illness, skin irritation, or systemic discomfort.

    • CAUTION (Slightly Toxic): Exposure induces minor physical irritation or short-term discomfort.

  • Eight Rules for Safe Handling:

    1. Read and comprehend the product label prior to open handling.

    2. Wear recommended Personal Protective Equipment (PPE) (gloves, mask, goggles, long sleeves).

    3. Calibrate liquid sprayer systems correctly prior to filling.

    4. Refrain from spraying operations during strong wind conditions to prevent off-target drift.

    5. Refrain from eating, drinking, or smoking throughout application procedures.

    6. Wash hands, body, and clothing thoroughly immediately post-application.

    7. Store chemicals in locked storage cabinets, away from food, feed, and children.

    8. Dispose of empty containers safely by triple-rinsing, physically puncturing, and returning to hazardous collection sites.

Pesticide Resistance Mechanisms and Management

  • Pesticide Resistance Process:

    • Mechanism: Resistance develops when target pests survive repeated exposure to a single chemical. Survivors pass genetic resistance traits to offspring. Over continuous generations, resistant individuals multiply until the pesticide fails entirely.

    • Evolution Steps: Initial Exposure (kills sensitive pests, leaving naturally resistant individuals) →\rightarrow Repeated Exposure (resistant survivors reproduce and pass on traits) →\rightarrow Result (pest population becomes dominated by resistant strains; pesticide loses control efficacy).

  • Primary Causes of Resistance:

    • Overuse: Excessive or unnecessary applications increase selective pressure on populations.

    • Repeated Use of Same Mode of Action: Exclusively using one mode of action continuously eliminates susceptible lineages, leaving only resistant mutants.

    • Incorrect Dosage: Sub-lethal dosages allow weakly resistant pests to survive, while excessive dosages increase extreme selection pressure.

    • Frequent Applications: Spraying too frequently exposes pest generations constantly, accelerating resistance cycles.

  • Resistance Management Strategies:

    1. Rotate Pesticide Groups: Rotate chemical families across different planting seasons.

    2. Alternate Modes of Action: Switch between products with distinct physiological modes of action.

    3. Use Recommended Rates: Follow exact dosage guidelines on product labels.

    4. Practice Integrated Pest Management (IPM): Use non-chemical tactics as primary protection.

    5. Avoid Unnecessary Spraying: Avoid fixed calendar spraying; apply chemicals only when field monitoring reveals economic threshold triggers.

    6. Use Resistant Crop Varieties: Plant crops bred with genetic insect or disease resistance.

    7. Conserve Biological Control: Protect indigenous natural enemies and beneficial predators.

    8. Practice Field Sanitation: Remove and burn/destroy diseased crop residues to eliminate overwintering pest populations.

Integrated Pest Management (IPM)

  • Definition: Integrated Pest Management (IPM) is a decision-making strategy combining cultural, mechanical, biological, genetic, and chemical tactics to achieve effective, economically viable, and environmentally sustainable pest control.

  • Five Essential Pillars of IPM:

    1. Cultural Control: Modifying farm operations and crop growth environments to prevent pest colonization.

    • Tactics: Crop rotation, proper plant spacing, organic matter enrichment, and adjusting planting/harvest dates.

    1. Mechanical Control: Using physical methods, tools, or physical barriers to remove or exclude pests.

    • Tactics: Handpicking pest populations, deploying sticky/attractant traps, installing row nets/barriers, and installing copper tape barriers.

    1. Biological Control: Exploiting natural organismal interactions to keep pest populations below damage levels.

    • Predators: Ladybugs, lacewings, ducks.

    • Parasitoids: Parasitoid wasps.

    • Pathogens: Bacillus thuringiensis (Bt), entomopathogenic fungi, viruses.

    1. Host Plant Resistance: Utilizing crop varieties that possess physical or biochemical traits that impair pest feeding, survival, and reproduction.

    2. Chemical Control (Last Resort): Deploying synthetic pesticides strictly when monitoring shows pest populations exceeding economic thresholds and non-chemical options fail.

    • Rules: Choose the proper chemical, apply at the recommended rate, respect Pre-Harvest Intervals (PHI), and ensure worker and environmental safety.