Question
I read one of your previous answers about giving these pests the boot but I want to be sure the timing of the chemical application is correct for my area and if you have any updates on the most effective chemical to use in view of the fact that some chemicals are no longer available.  My Blue Spruce became infested just last summer. I did not realize it until I saw the bags in late summer. The tree is about 12-15 feet tall and picking the bags is really not practical. I have a good sprayer with a 15 gallon tank and diaphram pump. Some internet articles say apply in May, some in June and some in July. Please advise the proper application information for my area. We are just north of Indianapolis, Indiana
Thank you.

Answer
In central Illinois bagworm egg hatch occurs in early to mid June. Pesticides are most effective if applied two weeks after egg hatch. In central Illinois control should begin in late June. An additional application is advised one to two weeks later to control later emerging caterpillars.


Just how did the bagworm make it to your tree? The newly hatched, tiny caterpillars move around by "ballooning". The young caterpillars climb high into trees. They produce a 2-3 foot long silk streamer that acts as a balloon to keep them drifting on the wind. Eventually they hit the side of a building or your favorite juniper. Feeding usually starts at the top of the tree.

According to Raymond Cloyd, U of I Extension entomologist, insecticides recommended for controlling bagworms include Bacillus thuringiensis kurstaki (sold as Dipel or Thuricide), cyfluthrin (Tempo and in some Bayer products) and spinosad (Conserve and some Ferti-lome products). Insecticide sprays are effective against the young larvae but bags that are 3/4 inch long or longer are very difficult to control. The bacterium Bacillus thuringiensis is effective on young caterpillars, but the material must be ingested--so thorough plant coverage is essential. Spinosad works very effectively by contact and ingestion. Cyfluthrin is recommended for larger larvae, but again thorough coverage is essential.