Bagworm season is here. Early control measures are the key to effective management. The following is an article on the subject.
Bagworm larvae are hatching, ballooning or feeding. Look for the 'dunce-cap' stage of feeding that occurs when larvae are very small and carry their bags with them in an upright position. Bagworm hatch occurs between 364 and 710 GDD (peaks at 580). Bagworms are caterpillars that prefer to feed on juniper, arborvitae, and Leyland cypress, but will eat a variety of other deciduous and coniferous plants. The bag is made up of small pieces of the plant the bagworm is eating and silk. The bags may look like pine cones or parts of the plant; thus it often is overlooked until damage becomes severe.
Larvae feed throughout the summer and begin to pupate around mid-August. Female bagworms pupate but remain in a flightless caterpillar-like state and release pheromones to attract males. Female bagworms lay 300 to 1,000 eggs in the bag after mating and die. The following summer the overwintering eggs hatch and disperse by ballooning on the wind to nearby plants. Although there is only one generation a year, damage may be encountered throughout the summer.
One control tactic is to physically remove the bags late fall through spring, but this is often too labor intensive or impractical because of tree or shrub size. Companion plants encourage parasitoids to remain in the area to attack bagworm pupae. Last summer, John Wiest and I evaluated the efficacy of Orthene (acephate), Dipel (B. thuriengensis 'kurstaki'), Conserve (spinosad) and Acelepryn (chlorantraniliprole) applied in late July without stickers. We discovered Acelepryn and Orthene provided similar levels of control (> 75%) whereas Conserve and Dipel provided less control of large bagworm larvae. Most bagworm eggs have hatched by middle to late June and applications of pesticides should be applied by July to target early instars. Products are more effective against smaller, younger caterpillars. Other products available include Confirm, Tempo, Permethrin Pro, or other pyrethroids.
Information from Brian Kunkel, Ornamental IPM Specialist, UD