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Bacillus thuriengiensis kurstaki (B.t.k.)

What is Bacillus thuriengiensis kurstaki (B.t.k.)?

Bacillus thuringiensis kurstaki (B.t.k.) is a naturally occurring bacteria found in the soil. An inactive, or spore, form of the bacteria is approved by the Environmental Protection Agency (EPA) for use as a pesticide to control the gypsy moth. B.t.k is commonly used by organic gardeners and is approved for use on more than 200 food and grain crops in the U.S. Over 100 million pounds are used each year in the U.S.

B.t.k. is harmful to moths and butterflies that are in their caterpillar stage. Caterpillars that eat B.t.k. on trees and shrubs die when the B.t.k. spores are activated in the insects' stomachs.

Are there any health risks associated with B.t.k.?

B.t.k. is not considered toxic for people, animals, birds, fish, and other insects such as bees and ladybugs. Also, it does not harm water supplies. Despite widespread use, B.t.k. has not been shown to cause infections in persons exposed through aerosol spraying either in the general population, children, or people with immune system disorders.

A small number of persons have reported symptoms including skin rash, irritation of the eyes, nose and throat, and hay fever-like symptoms after exposure to B.t.k. It is not known whether exposure to B.t.k. was responsible for the symptoms; however it is possible that these symptoms might be related to allergic reactions or irritation to a component of the spray product.

As a general precaution, Public Health - Seattle & King County recommends all persons in spray areas minimize exposure to B.t.k. Persons who are more susceptible to infections or respiratory irritation should pay particular attention to the precautions above. This includes people with an underlying illness such as leukemia, AIDS or other immune system deficiency, people receiving radiation or chemotherapy treatment, and people with asthma, emphysema or allergic sensitivities.

What precautions should be taken?

Even though B.t.k. has an excellent safety record, as a precaution, Public Health recommends:

  • Remain indoors for at least 30 minutes following the spray application. It's a good idea to keep family pets inside too.
  • Children should wait until moisture from the spray and dew has dried on grass and shrubs before they play outside, and they should wash their hands after playing outside. Gardeners should take the same precautions.
  • If you come in contact with the wet spray, wash the affected skin with soap and water. If wet material should get into the eyes, flush them with water for 15 minutes.

People who have concerns about possible exposure to B.t.k or concerns about their health or their immune system should contact their health care providers for advice

For additional information about the Gypsy Moth Eradication Project including current information about locations and dates of spraying, call the Washington State Department of Agriculture Gypsy Moth Hotline at 1-800-443-6684 or see the Gypsy Moth webpages at www.agr.wa.gov. You may also request to be notified by telephone or e-mail the day before any spray application is scheduled to occur.

To report an illness you think may be associated with gypsy moth spraying, call the Washington State Department of Health at 306-236-3360 or toll free at 1-888-586-9427.

Public Health - Seattle & King County has recorded information available 24 hours a day by calling 206-296-4949, tape 2, then press number 3. You may also call the Environmental Health Services Division at 206-205-4394.

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Gypsy Moth Control in King County
Gypsy Moth caterpillars can damage and kill trees and shrubs by eating leaves and needles. Gypsy Moth control using B.t.k. works by using a naturally occurring bacteria found in soil.