Bagworms overwinter as eggs inside the dead female’s bag. Young larvae normally hatch and emerge during mid- to late-May in Kansas. Now would be a good time to use control measures as earlier sprays may miss those who emerge from the bag later than normal. However, make sure the bagworms are present by looking for a miniature version of the mature bagworm. Also, check to be sure the bagworms are alive before spraying. Predators and parasites can sometimes naturally control this pest.
Insecticides commonly used for controlling bagworms include:
permethrin (38 Plus Turf, Termite & Ornamental Insect Spray; Eight Vegetable, Fruit & Flower Concentrate; Lawn, Garden, Pet, & Livestock Insect Spray)
bifenthrin (Bug Blaster II, Bug-B-Gon Max Lawn and Garden Insect Killer)
lambda-cyhalothrin (Spectracide Triazicide, Bonide Caterpillar Killer)
spinosad (Conserve; Natural Guard Spinosad; and Captain Jack's Dead Bug Brew).
Spinosad is an organic control that is very effective on this pest. Thorough spray coverage of foliage is essential for good control with any of these products. (Ward Upham)