Asked September 22, 2021, 3:56 PM EDT
Polk County Iowa
Thank you for your message and for contacting Iowa State University. Our online article about bagworms is at https://hortnews.extension.iastate.edu/bagworm
The bagworm caterpillars have finished feeding this season and insecticides sprayed now will have no affect. You are correct to pick off bagworms you can safely reach, and discard. Bagworm removal can happen anytime between now and next June, when the eggs inside the bags will start to hatch and start the next generation of caterpillars and damage.
The insecticide spray next spring should not be applied until the bagworms hatch, which is usually in June. Sprays are most effective against the tiny bagworms that are difficult to see.