The Time is Now to Control Bagworms

Bagworms are 1/8 to almost 2 inches long depending on age. Each bagworm is covered by a bag made of white silk with bits of the host plant spun onto the outer surface. Female bagworms are wingless, legless and grub-like (they never leave the bag). Males are small, brown hairy moths with dark wings that clear with age. Eggs are found in the mother's bag inside her pupal cast skins.

Bagworms occur throughout North Carolina. Bagworms have a very wide host range but are usually associated with arborvitae or juniper. A single bagworm does relatively little harm as it feeds on leaves. Excessive defoliation may kill conifers within one or two seasons. Damage is most noticeable in landscapes rather than woodlands. Occasionally, the silk band with which the bagworms attach themselves to a twig before they pupate girdles the twig as the twig enlarges. Winter is spent as eggs (500 to 1000) in the mother's bag.

They hatch in May, which is the best time to control them. The newly hatched larvae spin down on silken threads and are blown about by the early spring breezes. Most of the larvae land on the original host plant but some small worms may be "ballooned" for some distance on the silk thread. Upon reaching a suitable host, the worm begins to spin its bag and as it grows, it incorporates some of the host plant foliage into the bag for camouflage. As the bagworms grows, it enlarges the bag and adds fresh plant material to the outside. In August the worms mature and molt into the pupal stage. The bag is firmly attached by a sturdy silk band which the bagworms usually wrap around a twig. During August and September, male moths emerge from their bags to mate. After mating, females lay their eggs inside the pupal cast skins and die.

When practical, bagworms can be removed with scissors or a sharp knife. Bagworms are parasitized by several kinds of parasitic wasps. Insecticides are effective particularly when applied in late May early June when the bagworms are small and relatively sensitive. The following insecticides are labeled for bagworm control in the home landscape. pesticide (Trade Name)  Formulation  Amount of Formulation 

acephate (Orthene)  9.4 % emulsifiable concentrate  3 tablespoons per gallon of water.

  Bacillus thuringiensis B.t.( Biotrol, Dipel)  3.2 to 20 %  1 to 4.5 teaspoons per gallon of water depending on label directions. 

carbaryl (Sevin)  several formulations on the market; follow label directions. 

malathion (Cythion)  56 % emulsifiable concentrate  1-1/2 teaspoons per gallon of water. 

permethrin (Astro)  36.8 emulsifiable concentrate  1/4 to 1/2 teaspoon per gallon of water. 

For more information on bagworms or any gardening question please contact the Master Gardeners, 237-0113, 1-3 PM, Mondays, Wednesdays, and Fridays. They may also be reached via email at wilsonmastergardener@hotmail.com.

Recommendations for the use of chemicals included in this article does not imply endorsement nor discrimination against similar products or services not mentioned.

Date Created: 6/29/2004.