Bollworms are the most damaging pests of cotton across India and much of the world. They quietly eat the very part of the crop you want to harvest, the developing seed and lint inside the boll, so by the time the damage is obvious, the yield is often already lost. The key to good cotton bollworm control is catching the pest early and acting in the right order.
This guide explains how to tell the three main bollworms apart, how their lifecycle drives the damage, and a practical integrated pest management (IPM) plan, leading with cultural and biological steps and reserving sprays for when they are truly needed.
Which pest is the "bollworm"?
On cotton, "bollworm" actually covers three different pests, and good control starts with knowing which ones you have:
- American bollworm (also called cotton bollworm or gram pod borer), Helicoverpa armigera. A large, variable caterpillar that attacks many crops and bores bold, obvious holes into squares and bolls.
- Pink bollworm, Pectinophora gossypiella. A small, cotton-specialist whose tiny pink larva feeds hidden inside the boll, leaving very few signs outside.
- Spotted or spiny bollworm, Earias species. Caterpillars that first bore into growing shoots, causing them to droop, then move on to squares and bolls.
They often occur together, but they damage the crop in different ways and respond to slightly different tactics, so it pays to identify them correctly.
How to identify bollworm damage
Damage usually begins once the crop starts squaring (forming flower buds). Young larvae first feed on tender leaves, then bore into squares, flowers and bolls, eating the developing seed and lint inside.
Signs of American and spotted bollworm
- Round bore holes on squares, flowers and bolls, often with frass (excreta) packed around the entry point.
- Shed squares and bolls: attacked buds and young bolls turn yellow, dry and drop, or fail to open properly.
- Damaged locules: opened bolls show partly eaten, discoloured lint and chewed seed.
- Drooping shoots early in the season are a classic sign of spotted/spiny bollworm before it shifts to fruiting parts.
Signs of pink bollworm
Pink bollworm is sneaky, and its signs are far more subtle:
- Rosette bloom: infested flowers fail to open fully, with the petals twisted and stuck together into a tight rosette shape.
- Interlocked, stained lint: inside the boll the lint is matted, discoloured and stuck together, with damaged seeds.
- Hidden larvae: there may be almost no external hole, so you often need to open suspect bolls to find the small pink caterpillar inside.
If you are unsure which pest you are looking at, you can scan a damaged square, boll or leaf with the free Agrosphere app to help confirm the pest before you decide how to respond.
Understanding the lifecycle (and why it matters)
Adult moths lay eggs on the crop; the eggs hatch into larvae that do the feeding and boring, then pupate and emerge as the next generation of moths. Because the destructive larvae spend much of their life hidden inside squares and bolls, sprays only reach them in the brief window when eggs are hatching and tiny larvae are still on the surface. That timing is everything.
Two lifecycle facts shape almost every control decision:
- Helicoverpa armigera is highly polyphagous (it feeds on many crops) and can rapidly develop resistance to insecticides, so it must never be hit with the same chemical group again and again.
- Pink bollworm has, in many areas of India, developed resistance to Bt (Bollgard) cotton. This is exactly why Bt fields still get pink bollworm, and why a non-Bt refuge and full IPM remain essential.
An IPM plan for cotton bollworm control
Effective control is a layered programme, not a single spray. Start with the cultural and biological steps, which cost little and protect your sprays from burning out, and bring in insecticides only when thresholds demand it.
1. Scout and use thresholds
Walk the crop regularly from squaring onward, inspecting squares, flowers and bolls for bore holes and frass, and opening a few suspect bolls to check for pink larvae. Spray only when local economic threshold levels are crossed, rather than on a fixed calendar, so you treat real infestations and not the calendar.
2. Monitor and mass-trap with pheromones
Set up pheromone traps, gossyplure lures for pink bollworm and Helicoverpa lures for American bollworm, to track when moths are active. Rising catches tell you to scout harder and time any spray to egg-hatch. At higher densities, traps can also mass-trap males to reduce mating.
3. Use cultural controls
- Sow on time and prefer short-duration varieties so the crop matures and escapes the late-season build-up of bollworm.
- Avoid an extended or ratoon season, which gives the pest a year-round home.
- Destroy crop residue, stubble and unopened bolls after harvest, as these carry over pink bollworm larvae and break the lifecycle when removed.
- Plant the recommended refuge of non-Bt cotton with Bt fields to slow resistance.
4. Conserve and release natural enemies
Protect and encourage the helpers already in your field. Release Trichogramma egg parasitoids and conserve predators, and use biopesticides such as Helicoverpa NPV (a virus specific to the caterpillar) and neem-based products. Avoid broad-spectrum sprays early in the season that would wipe out these allies.
5. Use insecticides only when needed
When thresholds are crossed, targeted insecticides have a place. Active ingredients registered for bollworm in cotton include spinosad, emamectin benzoate, chlorantraniliprole, indoxacarb and others. Time sprays to egg-hatch when young larvae are exposed, rotate between different chemical groups to slow resistance, and choose timings that avoid harming pollinators and parasitoids.
Always read and follow the product label and local regulations for the correct dose, spray interval, pre-harvest interval and safety gear, and only use products registered for cotton in your region. Label rates and local rules take priority over any general guidance here.
Protecting pollinators and natural enemies
Cotton flowers are visited by bees and other pollinators, and your field is home to predators and parasitoids that quietly suppress bollworm for free. To keep them on your side, spray in the cooler parts of the day when bees are less active, never spray flowering crops carelessly, and lean on selective products and biopesticides wherever you can. Every spray you can avoid keeps these helpers working and slows the march of resistance.
When to act
Bollworm rewards growers who scout early and act in order: cultural and biological first, chemicals last and rotated. If you are seeing rosette blooms, frass-filled bore holes, or shed squares and bolls, the population is already established and needs a prompt, threshold-based response.
When you are not certain which pest is damaging your crop, scan a damaged boll or leaf with Agrosphere to help confirm the culprit and plan your next step. An accurate early identification is the difference between a manageable infestation and a serious loss, so trust your scouting, act early, and keep your control measures rotating.
Not sure which pest is in your field?
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Open AgrosphereFrequently asked questions
How do I control cotton bollworm?
Lead with IPM: scout regularly from squaring onward, sow on time, prefer short-duration varieties, and destroy crop residue, stubble and unopened bolls after harvest. Use pheromone traps for monitoring and mass trapping, conserve natural enemies, and apply biopesticides such as Helicoverpa NPV and neem. Spray insecticides only when economic thresholds are crossed, at the label rate, rotating chemical groups to slow resistance.
What are the signs of bollworm damage in cotton?
Look for round bore holes, often with frass (excreta) at the entry, on squares, flowers and bolls, plus shed squares and damaged locules. Pink bollworm shows subtler signs: a rosette bloom where petals are twisted and stuck together, interlocked or stained lint inside the boll, and damaged seed. You often need to open suspect bolls to find the pink larva.
What is the difference between pink bollworm and American bollworm?
American bollworm (Helicoverpa armigera) is a large, highly polyphagous caterpillar that bores obvious holes into squares and bolls and attacks many crops. Pink bollworm (Pectinophora gossypiella) is a small, cotton-specific pest whose tiny larva feeds hidden inside the boll, staining and interlocking the lint and damaging the seed, leaving few external signs.
Do pheromone traps work for bollworm?
Yes. Pheromone traps such as gossyplure for pink bollworm and Helicoverpa lures are very useful for monitoring moth activity so you can time scouting and sprays, and at higher trap densities they can mass-trap males to reduce mating. They work best as part of an IPM programme rather than on their own.
Why does Bt cotton still get pink bollworm?
In many areas of India pink bollworm has developed resistance to the Bt (Bollgard) toxins, so Bt cotton no longer reliably kills it. This is why Bt fields still get pink bollworm and why planting the recommended non-Bt refuge, along with full IPM, remains important to slow resistance.
When should I scout my cotton for bollworm?
Start scouting from the squaring stage, when flower buds appear, and continue regularly through flowering and boll development. Check squares, flowers and bolls for bore holes and frass, open suspect bolls for pink larvae, and watch pheromone trap catches. Act on local economic threshold levels rather than spraying on a fixed calendar.