Hi Clyde, the typical time to spray for bagworms for central IL is late June. I anticipate we will see an earlier spray date. we will know more once April has passed. you may want to check back. also the Home Yard and Garden Pest newsletter is a great resource for up to date info.
http://hyg.ipm.illinois.edu/ The first issue will be mid April and you can sign up to get a email notification. Sandy