Plant Disease

High Severity

American Bollworm / Pink Bollworm

Affects: Cotton · August–November (boll development stage is peak risk period)

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Causal Organism

Helicoverpa armigera (American bollworm); Pectinophora gossypiella (Pink bollworm — Bt-resistant)

Symptoms

American bollworm: entry holes in green bolls, frass visible. Pink bollworm (PBW): 'rosette' flowers that don't open; internal feeding of developing seeds in bolls; late-season lint damage.

Prevention

Use Bt cotton hybrids (effective against H. armigera but PBW resistance increasing). Pheromone traps at 5/acre for early detection. Refuge crop (non-Bt cotton or other host) mandatory. Destroy crop residues promptly after harvest.

Season Risk: August–November (boll development stage is peak risk period)

Treatment

Chlorantraniliprole (Coragen) 0.4ml/L for bollworm. For PBW-resistant populations: thiodicarb or quinalphos. Avoid pyrethroids — widespread resistance in both species.

Frequently Asked Questions

Why is Bt cotton no longer effective against pink bollworm?
Pink bollworm populations in Gujarat and Maharashtra have evolved resistance to Cry1Ac protein in first-generation Bt cotton. Cry2Ab hybrids ( bollgard II) are partially effective. KrishiAI tracks PBW Bt resistance alerts by district.

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Affected Crops

Cotton Farming Guide →