Plant Protection and IPM: Diagnosis, Thresholds and Safe Chemical Use
This domain tests diagnosis, threshold-based decision making and safe, correct use of pesticides inside an IPM programme. Marks are lost when a product quantity is confused with its active ingredient.
Diagnosis first
Distinguish insect pests (chewing: caterpillars, beetles; sucking: aphids, jassids, whitefly), diseases (fungal, bacterial, viral), nematodes, weeds and rodent damage. Sucking pests cause curling and honeydew; viral diseases are often spread by vectors, so vector control is disease control. Note the crop stage and the part affected before naming a cause.
IPM components
- Cultural: resistant varieties, timely sowing, crop rotation, clean seed, balanced fertilizer.
- Mechanical and physical: hand picking, light and pheromone traps, sticky traps, netting.
- Biological: Trichogramma egg parasitoids, NPV against Helicoverpa, Trichoderma and Pseudomonas for soil-borne disease, neem formulations.
- Chemical: only when the pest crosses the economic threshold level, using the right formulation and dose.
- Legal: quarantine and seed certification.
Worked example
A 50 WP formulation is recommended at 2 kg active ingredient per hectare, and the field is 0.5 ha. Product needed per hectare = 2 / 0.50 = 4 kg of formulated powder. For 0.5 ha = 2 kg, to be sprayed in about 250 litres of water. Reasoning: divide the active ingredient dose by the fractional strength of the formulation, then scale by area; spraying the active-ingredient figure directly as product over-doses the crop.
Traps that cost marks
- Confusing active ingredient with formulated product.
- Mixing EC formulations carelessly with hard water or with incompatible products.
- Spraying at midday in heat, increasing drift and phytotoxicity.
- Repeating one mode of action until resistance develops.
- Ignoring the pre-harvest interval, leaving residues in produce.