Bagworms feasting on cypress

Published 12:00 am Friday, July 20, 2007

Over the past few days many homeowners have called concerning bagworms on their leyland cypress and other shrubs. These immature insects are now out in force and will eventually kill leyland cypress and other coniferous shrubs such as junipers and arborvitae. Now is the time to thoroughly check susceptible plants for these insects even if they have not been a problem in the past.
Bagworms are 1/8 inch to almost 2 inches long depending on age. Each caterpillar or larvae spins a cocoon of white silk with bits of the host plant spun onto the outer surface. Larvae soon turn to dark brown pupae. The pupal or resting stage occurs inside the bag.
Adult female bagworms are wingless, legless and grub-like and never leave the cocoon. Adult males are small, brown hairy moths with dark wings turning clear with age. Eggs are extremely small and found in the mother’s bag inside her pupal cast skins.
As soon as the eggs hatch in May and June, the 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 are carried for some distance on the silk thread.
The worm begins to spin its bag and as it grows, it incorporates some of the host plant foliage into the bag for camouflage, making it difficult to recognize. As the bagworms grow, the bag becomes larger as fresh plant material is added to the outside.
In August, the worms mature and molt into the pupae 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 pupae cast skins and die.
Apparently, when the newly hatched larvae reach a plant which is different from its parent host plant, these insects often have difficulty in adapting to it and may die or may produce only a few offspring. After several years of struggling to keep from going extinct, the population may hit on the right combination of genes for the new plant and suddenly the new plant is covered with bagworms.
Small numbers of bagworms can be removed with scissors or a sharp knife. Bagworms can be parasitized by several kinds of parasitic wasps, however, if there are great numbers on the plant, insecticides are the only logical way to control the pest. Insecticides are effective if the bagworms are small and relatively sensitive, so it is very important to control these insects now while they are small. These insects are impossible to kill if allowed to pupate.
Insecticides such as Orthene, Dipel Sevin, Malathion or Conserve SC are labeled to control these insects. Complete coverage is necessary to control these pests. Always read and follow the label before applying any pesticide.
Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension Service in Rowan County. For archived garden columns or other information, visit the Rowan County Master Gardener Web site at www.rowanmastergardener.com , e-mail Darrell_Blackwelder@ncsu.edu or call 704-216-8970.

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