For Release May 29, 2005

Bagworm Treatment Time Is Near

by Chuck Otte, Geary County Extension Agent

This is Memorial Day Weekend and the first of June looms ahead. This is an important time of year, and not just for brides and grooms. THE major pest of junipers or cedars is the bagworm. And the nefarious little rascals are in the process of hatching. Considering the warm weather we've had in May, we can pretty well assume that they have all hatched, and it's time to get treating.

Let's back up and review the biology of these rascals. Bagworms are not the caterpillars in the big webby masses on the ends of trees that we see in late summer, this is a common misunderstanding. The bagworm feeds primarily on junipers or cedars and the larvae form those cute little "bags" that they decorate with foliage from the host plant. While well known for preferring the junipers as their host, they have been documented for feeding on over 200 species of trees and shrubs. The larvae stage is the only damaging life stage this insect has, but it can be quite destructive if not controlled.

As an adult, the bagworm is a moth. The female is wingless and, after becoming an adult, attracts the male, they mate and she fills the bag that housed her cocoon, or pupae, with up to 1,000 eggs. These eggs have hatched, or are in the process of hatching right now. The young bagworm larvae leave the bag and immediately starts feeding on the host plant quickly forming a tiny little bag and covering it with bits of foliage from the host. For the first few weeks, this larvae grows very slowly and is easily overlooked by most homeowners. But as they grow they make bigger and bigger bags. Initially, the foliage that they decorate their bag with is green, but by the end of the feeding season, when the bags are close to two inches in length, the foliage turns brown and the bag becomes very apparent.

Fortunately, bagworms are very easy to control. But timing is everything. If you wait until late summer when they have grown very large and already done a lot of damage, they can be very difficult to control however. If you had bagworms last year, whether you treated or not, you need to treat this year. Just one missed female bagworm from last year will provide hundreds of offspring to snack on your junipers this year. If you had a neighbor with infested trees close to yours, then you may want to treat also as the older bagworm larvae will actually crawl up to a few hundred feet to reach a new food source.

Bagworm treatment normally starts the first part of June. At this time the eggs should have all hatched, the larvae are small and easily controlled. If homeowners will use two sprays in June, about two weeks apart, they can expect excellent control. Starting early gives you the advantage of using the biological control bT or Bacillus thuringiensis. This is effective if used on small larvae, but not a good choice for treating in late July. There are many traditional pesticides that will also work. Check the label to see if they are approved for controlling bagworms.

The key control action is to apply whatever product you are using with a lot of water. Use a hose end sprayer, those sprayers that attach to the end of your garden hose. Soak the foliage to the point of runoff, which may be a lot of product if you have large trees as opposed to traditional juniper shrubs. Bagworms can be devastating if not noticed, and treated, early in the season. Start inspecting your junipers now for evidence of old, or new bagworm activity!


Return to Agri-Views Home Page

Return to Ag Home Page