When to spray for bagworms Posted By: Ben Butler May 27, 2009 @ 4:29 am Today's Local News Tweet Share Email The Keokuk County Extension is urging property owners to hold off on spraying for bagworms. Education Director Gary Bickmeir says there has been considerable interest in Southern Iowa as people worry about the caterpillars defoliating their trees. For more information contact the Keokuk County Master Gardeners, or the Keokuk County Extension office.