Plant Protection: Recognising Pests and Diseases, and Acting at ETL
Major problems in Assam
Rice: yellow stem borer (dead hearts, white ears), brown planthopper (hopper burn), leaf folder and gall midge. Mustard: aphid. Pigeon pea: pod borer. Tea: tea mosquito bug and blister blight. Vegetables: fruit borer of tomato and brinjal, diamondback moth of cabbage.
Disease logic
Blast (Magnaporthe oryzae) gives spindle-shaped lesions; bacterial leaf blight (Xanthomonas oryzae pv. oryzae) gives water-soaked margins turning straw-coloured; sheath blight (Rhizoctonia solani) attacks the leaf sheath near the water line. The rule that earns marks: fungi respond to fungicides, bacteria have no effective chemical cure (use resistant varieties and sanitation), and viruses are managed by controlling the vector.
IPM rules
- Scout first; treat at economic threshold level, not by calendar.
- Conserve natural enemies; avoid early pyrethroid sprays that trigger hopper resurgence.
- Rotate modes of action to slow resistance.
- Respect label dose and pre-harvest interval.
- Sanitation: destroy stubble, remove infected tillers.
Worked example
A 1-ha Sali field is scouted in ten random 1 m² quadrats. Total dead hearts = 40 out of 2,500 tillers = 1.6 per cent, below the 5 per cent vegetative-stage ETL for stem borer. Decision: no insecticide; re-scout after seven days and consider Trichogramma release or pheromone traps. Had the count crossed ETL, a recommended granular formulation applied to the whorl would be justified.
Traps that cost marks
- Spraying a fungicide for a virus problem.
- Using trap catches as damage counts instead of field scouting data.
- Quoting an ETL without naming the crop stage.
- Ignoring the pre-harvest interval when recommending a product.