Pink bollworm in BG-II cotton: trap counts, a dealer's tank mix and when to stop picking
Harjeet farms 3.2 ha of BG-II hybrid cotton near Dabwali, Sirsa, sown on 5 May. By the first week of September he has already given four sprays - three of lambda-cyhalothrin and one of chlorpyrifos - each time because "worms were seen". His five pheromone traps per hectare caught 11, 13 and 16 moths per trap per night on three consecutive nights. On 50 plants he counts four rosette flowers and finds pink larvae inside green bolls with exit holes. The local dealer is pressing him to spray a pyrethroid plus acephate tank mix because neighbouring fields are spraying, and each spray costs him ₹1,450 per hectare. Kapas is fetching ₹7,200 per quintal and his expected yield has already slipped. He asks whether the trap catch really means he must spray at once, whether the same mixture will work, and how long he should go on picking.
1. Interpret the trap catch against the action threshold and decide whether a spray is justified now.
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Threshold check. For pink bollworm the accepted action threshold is 8 moths per trap per night for three consecutive nights. His catches of 11, 13 and 16 clearly cross it, so this is not a false alarm.
Confirm the signal is real before acting. Traps must be placed about 15 cm above the canopy, five per hectare, with lures changed every three weeks; a trap hanging in a tree or an old lure gives misleading counts. His rosette flowers and larvae with exit holes in green bolls confirm that the population is established and reproducing in the field, not merely migrating through.
Decision. A control action is justified - the crop is in the boll stage, so each larva entering a boll damages fibre directly and opens the boll to rot. But the threshold tells him when to act, not what to use. Reaching for the same pyrethroid mixture again is a separate question, and the answer there is no.
2. Give the spray recommendation and the non-chemical measures you would combine, explaining why a pyrethroid + acephate mix is a poor choice here.
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Why the dealer's mix is wrong:
- Three pyrethroid sprays are already on the field this season; repeated use of one mode of action selects resistant pink bollworm and flares whitefly by killing natural enemies.
- Acephate is an organophosphate with no special fit against bollworm inside bolls, and tank-mixing several insecticides raises cost, residue risk and hazard to the sprayer without adding control.
- Pink bollworm in North India has a documented history of resistance to pyrethroids and reduced susceptibility to Bt toxin, so "more of the same" is exactly the wrong strategy.
What to do: choose an insecticide from a different mode-of-action group not yet used this season (for example a Group 28 diamide), at the label dose, in about 500 litres of water per hectare, sprayed in the evening so the spray deposits on bolls and the sprayer is not exposed to peak heat. Check the label's pre-harvest interval - bolls will be picked soon - and confirm the molecule is currently approved for pink bollworm.
Non-chemical measures, which matter as much:
- Pick and destroy rosette flowers and fallen squares daily for a week; this breaks the cycle cheaply.
- Do not leave ratoons or unpicked plants standing after harvest.
- Use mating disruption (gossyplure rope) where the local extension service supplies it.
- Keep a spray diary with date, molecule, dose and cost, and stop spraying mixtures "because the neighbour sprayed".
3. Advise on crop termination and picking so the pest does not carry over, and show what the sprays are costing him.
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Cost check. Four sprays already cost 4 × ₹1,450 = ₹5,800/ha; six would mean ₹8,700/ha. At ₹7,200 per quintal, kapas is ₹72 per kg, so every single spray must save about 1,450 ÷ 72 ≈ 20 kg of kapas per hectare just to pay for itself - before counting the sprayer's time, water and health risk. That is the test to apply before agreeing to another round.
Termination. Do not stretch the crop for a late fifth pick. Complete picking by the end of October, then cut and shred the stalks, incorporate them and deep plough, so larvae surviving in bolls, seed and stalk do not carry into next season. Pink bollworm moths fly across field boundaries, so this has to be done by the whole village, not one farmer - a single unharvested patch undoes everyone's effort. Check the current year's state advisory for the exact termination date and stubble-shredding deadline in Sirsa district.
Also: do not store unpicked kapas beside the field, and keep the gin waste away from the farm, because both carry live larvae. Plan next year's sowing window and variety choice with the extension officer rather than repeating the same hybrid and the same spray calendar.