Failed spray sequence in chilli before first harvest
Sanjay Behera grows 0.6 ha of chilli (cv. Utkal Ava) in Ganjam district. The crop is 60 days old and the first harvest of green chilli is due in 10 days. Leaves are curled upward with silvery streaks, and young leaves are bronzed and brittle; he also sees downward curling of margins and a few reddish mites. He has sprayed imidacloprid 17.8 SL, followed by fipronil 5 SC, then abamectin 1.9 EC, then spiromesifen 22.9 SC, each at 4–5 day intervals, often in the afternoon. Thrips counts remain at 25–30 per leaf. He now wants to tank-mix lambda-cyhalothrin + profenophos with diafenthiuron and spray tomorrow, and he asks whether he can harvest three days later. He sells green chilli to a local trader who has rejected loads with visible residues. His neighbour recommends spraying every alternate day until the pest disappears.
1. Diagnose the pest complex and explain why the spray sequence failed, using evidence from the field and his practice.
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The field shows a mixed thrips and mite problem: upward leaf curl, silvery streaks and bronzing indicate thrips (Scirtothrips dorsalis); downward curling of margins and reddish mites indicate the broad mite or yellow mite (Polyphagotarsonemus latus). The spray sequence failed for several reasons. Imidacloprid and fipronil are not reliable against the mite, while abamectin and spiromesifen target mites but were applied only 4–5 days apart, which selects for resistance and does not allow the population to be assessed. Afternoon spraying at 32–35°C increases evaporation and phytotoxicity and gives poor coverage of the underside of leaves where thrips feed. Repeated broad-spectrum sprays also kill natural enemies, causing mite flare-up. Tank-mixing a pyrethroid with profenophos and diafenthiuron would add three modes of action at once, increase residue risk and is not justified by the scouting data.
2. Prepare a 10-day action plan that protects the harvest and reduces resistance risk. Include non-chemical measures and a spray decision rule.
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Plan for the next 10 days: stop all sprays for at least 3 days and scout 20 plants across the field, recording thrips and mites per leaf and beneficial insects. Remove severely curled leaves and destroy them. Install blue sticky traps for thrips and avoid excess nitrogen. For a harvest due in 10 days, choose only label-approved products with a pre-harvest interval shorter than the harvest date; verify the label rather than relying on the dealer. Rotate modes of action: if a mite product is needed, use one with a short PHI and not the same group as abamectin or spiromesifen; if thrips are above the action threshold, use a single effective product rather than a tank-mix. Spray early morning or late evening, direct the nozzle to leaf undersides, and do not spray if rain is expected within 6 hours. Harvest only after the stated PHI. Do not spray every alternate day.
3. What would you tell him about the trader's residue concern and about record-keeping?
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The trader's rejection risk is real. Tell him that residue is a function of product, dose, number of sprays and the interval to harvest, not of how often he sprays. Keep a spray diary with date, product, dose, area and PHI, and keep empty containers or labels. Do not harvest three days after diafenthiuron or a pyrethroid; check the label PHI and add a safety margin. If the crop is due for harvest and pests are still present, use non-chemical options - removal of affected shoots, water jets, neem-based products with a short waiting period - rather than a risky spray. A rejected load costs more than a slight yield loss.