Begin scouting conifer windbreaks for small bagworm ‘dunce caps’ or ‘ice cream cones’. Small bagworms hold their conical bags upright. These are early instar larvae. We have now accumulated enough degree days for eggs to hatch out of last year’s bags. Eggs will continue to hatch over the course of the next couple of weeks.
Duncecap stage (circled) – Control is easy at this size
Bagworm larvae hatcing out of last year’s bags
Lepidopteran larvae tend to eat about 80% of their total food intake during their final instar which, for bagworms, occurs in August. August is when damage is extremely visible, but it is NOT the time to treat for them – large larvae are hard to kill and may have already done their damage. Between now and early July, larvae will be small, less than a half inch. Picking bags is no longer a control option as eggs have hatched. There are several modes of action that are effective on them, including organophosphates (ex Orthene), carbamates (ex carbaryl), Bt, spinosyns, and pyrethroids.
Adult stage bagworms