For Release June 11, 2002

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

If I were to pick one insect that has generated the most calls the past few years, it would probably have to be the bagworm! Bagworms are the little insects that attack primarily cedars or junipers, but will feed on over 200 species of plants. If a bagworm infestation becomes severe enough it can kill a juniper tree or shrub.

Bagworms are the larval, or caterpillar, growth stage of a small, rather plain moth. The larvae form silken bags that they adorn with bits of foliage from the host plant. This camouflage is very effective in preventing most homeowners from seeing the little rascals until late in the season when substantial damage has already been done.

Bagworms overwinter as eggs in the silken bag that had housed the female bagworm. This bag can hold several hundred eggs. The bagworm eggs hatch slowly over a period of four to five weeks starting in mid to late May. This year, because of the cool May weather, they probably started hatching a little later. We want to minimize how many times we need to spray, thus minimizing the amount of control product we have to use. We also want to treat early, when the bagworms are small and easy to control. If we wait until late July or August, when the damage is visible as you drive by, the bagworms are harder to control and there has been much more damage.

How do you know if you need to treat your junipers/cedars? Did you have bagworms last year? Even if you sprayed, you will want to treat again this year. Do you have next door neighbors that had bagworms last year? If so, you will probably want to treat again this year. The female bagworm is wingless and has to lay her eggs in her bag. However, young bagworms can crawl as far as a couple hundred feet to a new food source. If neither you or your neighbors had bagworms last year, simply go out weekly and inspect your junipers, and blue spruce trees, for little bagworms. You’ll need to look close because the little bags will be covered with bits of foliage from that host plant.

If you wait until about mid-June for the first treatment, and then wait two weeks and treat again, you can usually get by with just two treatments. If you are using the biological control product bT, Bacillus thuringiensis, you can start a little earlier and spray every week until late July. The bT products are effective, but they take a little longer to work and need to be applied more often to make sure the active bacteria is eaten by the little bagworms.

There are many insecticide products that are labeled for bagworms and most of them do a very good job. The secret to success is not what product you use, but how you apply it. For effective bagworm control you need to apply a lot of mixed spray. The plants need to be sprayed to the point of thorough saturation. Even for a small tree or shrub you can not do this with a pump up one gallon canister sprayer. You will need a hose end sprayer that will allow you to put out a lot of spray. If the trees you need to treat are in a remote area or you have large trees you will probably need to hire a professional spray service.

Bagworms have become wide spread in our area and they can do a lot of damage if left uncontrolled. Start checking your susceptible plants now, and prepare to treat if a bagworm infestation is found!

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