🐛 Organic Pest, Disease and Weed Management

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Organic Pest, Disease and Weed Management

The Organic IPM Pyramid

Organic crop protection follows a strict hierarchy of preferences, often visualized as a pyramid — preventive and ecological methods form the wide base, while material-based interventions are the narrow apex used only as a last resort:

1. Prevention (base): resistant varieties, crop rotation, sanitation, healthy soil
2. Monitoring: regular scouting; pest/disease threshold assessment
3. Cultural control: time of planting, trap crops, polyculture, habitat management
4. Biological control: beneficial insects, predators, parasitoids, microbial agents
5. Approved organic pesticides (apex/last resort): botanicals, copper, sulphur, Bt

This approach contrasts with conventional farming where chemical pesticides are a first-line response.

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Organic Disease Management

Preventive Strategies

Resistant varieties: The most effective and cost-free method — choose varieties with genetic resistance to locally prevalent diseases. No inputs needed.

Crop rotation: Breaking the disease cycle by changing host crops. Minimum 2–3 year rotation prevents build-up of soil-borne pathogens. Rice–wheat rotation is less effective than rice–legume–wheat.

Balanced nutrition: Excess nitrogen (N) produces soft, lush, succulent tissues that are highly susceptible to fungal attack. Organic nutrient management inherently avoids N excess.

Field sanitation: Remove and destroy infected plant debris; do not compost diseased material unless hot composting (55–65°C kills pathogens).

Seed Treatments

Treatment	Active Ingredient	Target	Rate
Beejamrit (ZBNF)	Cow dung + urine + lime + soil	Seed-borne and soil-borne fungi	Coat seeds; soak 6–8 h
Trichoderma (powder)	T. viride / T. harzianum	Fusarium, Pythium, Rhizoctonia	3–4 g/kg seed
Pseudomonas fluorescens	Induced Systemic Resistance (ISR)	Foliar + soil-borne diseases	10 g/kg seed or 2.5 kg/ha soil
Neem cake extract	Azadirachtin + neem oil	Soil-borne pathogens, nematodes	250 kg cake/ha soil incorporation

Approved Chemical Treatments (Organic-permitted)

Bordeaux Mixture:

• Composition: CuSO₄ (copper sulphate) + Ca(OH)₂ (slaked lime) in 1:1 ratio
• Permitted under NPOP with restrictions: maximum 6 kg Cu/ha/year
• Applications: late blight of potato and tomato (Phytophthora infestans), downy mildew of grapes and cucurbits, anthracnose
• Precaution: copper accumulates in soil; use minimum necessary quantity

Wettable Sulphur:

• Effective against powdery mildew (all crops) and mites
• Permitted in organic; apply as dust or wettable powder spray
• Avoid in high temperatures (>35°C) — phytotoxic

Trichoderma (soil application):

• T. viride, T. harzianum: antagonistic to Fusarium wilt, damping-off (Pythium, Rhizoctonia)
• Apply 2.5 kg/ha with FYM or vermicompost as carrier; also effective as seed/seedling root-dip treatment

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Organic Pest Management

Botanical Pesticides

Neem (Azadirachta indica) — the cornerstone of organic pest management:

• Active ingredient: Azadirachtin (limonoid terpenoid)
• Mode of action: Insect Growth Regulator (IGR) — disrupts moulting; antifeedant; repellent; oviposition deterrent
• Formulations:
  • NSKE 5% (Neem Seed Kernel Extract): crush neem kernels; soak in water; filter; spray
  • Neem oil 3%: emulsifiable; antifeedant + direct contact
  • Neem cake: soil application; controls soil-borne insects and nematodes; 250 kg/ha
• Target pests: sucking pests (aphids, whitefly, thrips, jassids), leaf miners, caterpillars, soil insects
• Residue-free: decomposes rapidly; no food safety concerns

Pyrethrum (Chrysanthemum cinerariifolium):

• Active ingredient: pyrethrins (natural); NOT synthetic pyrethroids
• Mode of action: contact and stomach; affects insect nervous system
• Permitted in organic (natural form); broad-spectrum; breaks down rapidly in sunlight
• Apply in evening to protect beneficial insects (bees active in daytime)

Tobacco (Nicotiana tabacum):

• Active ingredient: nicotine
• Preparation: 4% tobacco decoction (boil 400 g tobacco in 10 L water, strain, dilute to 10 L)
• Target: soft-bodied pests — aphids, thrips, mealybugs
• Note: toxic to bees and beneficial insects; use carefully

Mahua (Madhuca longifolia):

• Saponin-rich seed cake; broad-spectrum insecticidal and nematicidal when incorporated in soil

Entomopathogenic Organisms (Microbial Pesticides)

Agent	Target Pest	Application	Notes
Bt (Bacillus thuringiensis)	Lepidoptera larvae (caterpillars)	Foliar spray; ingestion required	Cry proteins; highly specific; permitted in organic
Beauveria bassiana	Soil insects, thrips, whitefly, beetles	Soil drench or foliar	Entomopathogenic fungus; infects through cuticle
Metarhizium anisopliae	White grubs, soil insects, locusts	Soil application	Entomopathogenic fungus
NPV (Nucleopolyhedrovirus)	Spodoptera, Helicoverpa	Foliar spray at dusk	Highly specific; pest-specific virus
Steinernema / Heterorhabditis (EPN)	Soil-dwelling grubs, root pests	Soil drench	Entomopathogenic nematodes

Physical and Mechanical Pest Control

Method	Target Pest	Details
Yellow sticky traps	Whitefly, aphids, leafminer, winged aphids	25 traps/ha; replace when filled
Blue sticky traps	Thrips	Specific to thrips colour preference
Pheromone traps	Spodoptera, Helicoverpa, fruit flies	Mass trapping or population monitoring
Light traps	Nocturnal insects (stem borers, cutworms)	Solar-powered LED traps; 1/ha
Bird perches (T-stakes)	General insects	Raptors and insectivorous birds hunt pests; 25 perches/ha in rice

Cultural Practices for Pest Management

• Trap crops: Sesbania or Napier grass borders for stem borers; African marigold for Helicoverpa
• Intercropping: polyculture reduces pest host concentration; e.g., maize + cowpea
• Altered planting dates: avoid peak pest emergence windows
• Crop rotation: breaks pest and disease cycles

Predators and Parasitoids

Beneficiary	Type	Pest Controlled
Chrysoperla carnea (lacewing)	Predator	Aphids, mites, whitefly, mealybug
Trichogramma chilonis	Egg parasitoid	Stem borers, Helicoverpa, Spodoptera
Cotesia plutellae	Larval parasitoid	Diamondback moth caterpillars
Ladybird beetle	Predator	Aphids, mealybugs, scales
Spiders, ground beetles	Predators	General soil and foliage pests

Parasitoids are commercially available as Trichogramma cards (1 lakh eggs/card; 5 cards/ha/week).

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Organic Weed Management

Weed management without synthetic herbicides requires diversified strategies and is often the most labour-intensive aspect of organic farming.

Mechanical and Physical Methods

Method	Description	Crops
Hand weeding	Most effective; labour-intensive; 2–3 rounds/season	All crops
Hoeing	Wheel hoe, hand hoe; disrupts weed seedlings	Row crops
Rotary weeder	Mechanical hand-pushed; rice, vegetable rows	Paddy, vegetables
Flame weeding	Propane torch; kills weed seedlings (not seeds)	Nursery beds, organic farms

Mulching

Mulching is the most effective organic weed suppression strategy:

• Straw mulch (5–10 cm layer): wheat or rice straw; suppresses 70–80% weeds; also conserves moisture and moderates soil temperature
• Black polyethylene mulch: complete weed elimination under mulch; used with drip irrigation in high-value vegetables
• Coir mat / weed mat: long-lasting; used in orchards and plantation crops
• Living mulch: low-growing legumes (white clover, cowpea) inter-planted with main crop; competes with weeds and fixes N

Cover Crops and Allelopathy

Cover crops between cash crop seasons reduce weed pressure:

• Mustard (Brassica juncea): allelopathic; glucosinolates suppress weeds and soil-borne pathogens
• Sorghum: allelopathic; sorgoleone residues suppress weed germination
• Sunflower residue: allelopathic terpenoids suppress broad-leaved weeds
• Rye (Secale cereale): heavy biomass; excellent weed suppressor as winter cover crop

Solarization

Soil solarization: tarping moist soil with transparent polythene in peak summer:

• Raises soil temperature to 50–60°C in the 0–10 cm layer
• Kills weed seeds, soil-borne pathogens, nematode eggs
• Duration: 4–6 weeks in summer
• Effective in regions with high solar radiation (India: April–June)

Stale Seedbed Technique

1. Prepare seedbed well; irrigate
2. Allow first flush of weed seeds to germinate (10–14 days)
3. Shallow tillage (2–3 cm) or flame weeding to kill emerged weed seedlings
4. Repeat 1–2 times if time allows
5. Plant the main crop into a depleted weed seed bank

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Pest Incidence During Organic Transition

Pest and disease incidence is typically higher during the 2–3 year transition period from conventional to organic:

• Beneficial insect populations not yet re-established
• Soil biology still recovering
• Farmer learning curve for organic pest scouting and response

After establishment, biodiversity builds — natural enemies increase, soil health improves, plant immunity strengthens — and pest pressure generally stabilizes at manageable levels.

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Organic Pest Management Summary Table

Pest / Problem	Organic Control Measure	Timing	Effectiveness
Aphids	Neem NSKE 5%, pyrethrum spray, Chrysoperla release	At first colony	High
Whitefly	Yellow sticky traps, Beauveria spray, neem oil	Continuous trapping	Moderate–High
Stem borers (Lepidoptera)	Bt spray, Trichogramma release, light traps	At egg laying / early instar	High
Helicoverpa / Spodoptera	NPV spray, pheromone traps, Bt, neem	Egg mass scouting → early	High
Soil grubs (white grubs)	Beauveria, Metarhizium soil drench, neem cake	Pre-sowing soil treatment	Moderate
Powdery mildew	Wettable sulphur (0.2%), neem oil	At first symptoms	High
Late blight	Bordeaux mixture (1%), copper hydroxide	Preventive; rainy season	High
Fusarium wilt	Trichoderma seed + soil treatment	Seed treatment + basal	Moderate
Weeds	Mulching + hand weeding	Season-long	High (combined)
Nematodes	Neem cake, Paecilomyces, solarization	Pre-sowing	Moderate

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Key Facts for Examination

• NPOP maximum copper use: 6 kg Cu/ha/year
• Bordeaux mixture composition: CuSO₄ + Ca(OH)₂
• Neem active ingredient: Azadirachtin (IGR — Insect Growth Regulator)
• NSKE concentration for organic spray: 5%
• Bt (Bacillus thuringiensis) target: Lepidoptera larvae
• Trichoderma seed treatment dose: 3–4 g/kg seed
• Solarization temperature achieved: 50–60°C at 0–10 cm depth
• Pheromone traps primarily used for: monitoring and mass trapping of Spodoptera, Helicoverpa

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Organic IPM pyramid, botanical pesticides, biocontrol agents, copper-sulphur fungicides, and mechanical/mulching/cover crop weed management strategies.
Section context	Revise this lesson with the rest of Organic Crop Protection for stronger conceptual continuity.