Thrips Damage and Spray Failure in Chilli Before First Picking
A farmer in Jalna has 0.6 ha of chilli (cv. Teja) at 60 days after transplanting. Leaves on the upper canopy curl upwards, are crinkled and reduced, internodes are short, and 20–25% of plants are stunted with heavy flower drop. A hand lens shows tiny elongated insects in flowers and on lower leaf surfaces. The farmer has sprayed imidacloprid 17.8 SL at 0.5 ml/L three times at 7-day intervals, followed by profenofos 50 EC; symptoms continue on new growth. Day temperature is 36°C and the weather is dry. First picking is due in 20 days, and a trader has offered a premium for residue-tested chilli. Neighbouring plots of a different variety show less damage. The farmer wants to spray a pyrethroid mixture and harvest in five days.
1. Diagnose the problem and explain why the sprays failed.
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Upward curling, crinkling, short internodes, flower drop and thrips in flowers fit thrips (Scirtothrips dorsalis) damage, often called “murda”. Chilli leaf curl virus also causes curling, but typically downward curling, puckering, mosaic and thickened leaves, with whitefly rather than thrips; some plants may have both. The sprays failed because imidacloprid was used three times, selecting resistant thrips; thrips hide in flowers and leaf whorls, so coverage was poor; profenophos alone does not cover eggs or all stages; and hot, dry weather favours rapid multiplication. A pyrethroid is likely to worsen resistance and can flare mites.
2. Design a resistance-managed spray programme for the next three weeks, including PHI and residue safety.
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Rotate modes of action rather than repeating one molecule: for example spinetoram, cyantraniliprole, emamectin benzoate or diafenthiuron, applied in early morning or evening with a non-ionic surfactant and directed at flowers and leaf undersides. Use blue sticky traps to monitor. Do not repeat the same mode of action within a thrips generation, and avoid pyrethroids. Observe label PHIs - most of these molecules carry roughly a 5–10-day PHI on chilli - and with first picking in 20 days, plan the last spray at least 10 days before harvest. Do not harvest five days after a pyrethroid. The residue-tested premium is worth more than the spray cost, so keep spray records and choose short-PHI products.
3. What cultural and long-term measures would you add?
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Rogue plants with virus-like symptoms - mosaic, severe distortion, thickening - because they are a virus reservoir and cannot be cured. Manage whitefly with yellow traps, a border crop, reflective mulch and selective insecticides. Avoid excess nitrogen, which produces soft growth that thrips prefer. Conserve natural enemies such as Chrysoperla and Orius by avoiding broad-spectrum sprays. For the next season, use healthy seedlings, a thrips-tolerant variety where available, and a planned rotation of modes of action from the nursery stage. If virus incidence is above about 10%, remove affected plants promptly and reassess the source of seedlings.