Big green caterpillars eating my cotton bolls and flowers

Large green to brown caterpillars boring clean round holes into bolls with the rear of the body sticking out is typical of American bollworm Helicoverpa. BT cotton suppresses it but not fully, especially in late or stressed crops. Monitor with pheromone traps and check plants in the morning for fresh holes and larvae. On threshold use HaNPV biopesticide for small larvae, encourage birds with perches, and on heavier attack spray a recommended insecticide rotating modes of action, keeping diamides and other costly groups for when really needed. Avoid repeated pyrethroid use which can cause resistance and flare sucking pests. Collect and destroy bored bolls. Follow label dose and PHI and confirm the current schedule with your KVK or CICR. Keeping the BT refuge as in the seed packet also helps slow resistance.