Landscape and Nursery - More on Bagworms

Bagworms are getting larger where they are found, especially on susceptible evergreens. Control measures should be applied without delay as bagworms are very hard to kill when they get large.

Bagworms are creating protective bags that are about 0.5 – 1.0” in length at this point in the season. Observe arborvitae, junipers and Leyland cypress for presence of bagworms.
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 in late summer to early fall. Female bagworms lay 300 1,000 eggs in the bag after mating in the fall 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. Weather conditions and parasitoids often keep bagworm populations under control without human intervention. Control with chemicals is best achieved when applications are made when the insect is small. Products available for control are sprays of B.t.'kurstaki' (i.e. Dipel), insect growth regulators (IGR's) such as Confirm (tebufenozide), or reduced-risk products like Conserve (spinosad). Compounds such as Tempo or Permethrin Pro or other labeled pyrethroids control older larvae as does acephate (Orthene). Applications are best made before the end of June and coverage is important for the best results. For control now in mid-July, Conserve will still work, the pyrethroids are an option, as is Orthene.

Information from the ornamental IPM programs at University of Delaware and University of Maryland.