Gypsy Moths

Page Content Source:  Washington State Department of Health            Click the image below to see the treatment areas

Gypsy Moth Spray AreaWhat are gypsy moths?

Gypsy moths are an invasive pest species in Washington. As caterpillars, they can eat hundreds of different types of plants and trees. They lack native predators and diseases, so their populations can increase quickly if they are not controlled. The Department of Agriculture has a monitoring and eradication program to keep gypsy moths from establishing a permanent breeding population in Washington.

How are gypsy moths controlled?

Washington State uses an integrated pest management approach to control gypsy moths. This includes:

  • Extensive monitoring with pheromone traps.
  • Visual inspection for egg masses to determine where a breeding population is located.
  • Manual destruction of egg masses.
  • Targeted control for caterpillars with least toxic methods effective for the site. Btk is the most commonly used product for gypsy moth control in Washington.
  • Follow-up trapping to evaluate success of eradication.

What is Btk?

Btk, or Bacillus thuringiensis kurstaki, is a naturally occurring bacteria found in soil. It is a commercially produced pesticide (sold as Foray) and sprayed on tree and plant foliage to control caterpillars. When caterpillars eat sprayed leaves, they stop eating and die. The product is very specific to caterpillars and has been shown to have very little toxicity to mammals, birds, fish, or insects such as honeybees, beetles, and spiders. Btk is extensively used in organic agriculture and is available in many home gardening products. In addition to Btk, the commercial product also contains ingredients to make it stick to plant leaves, and has residues of food crops and preservatives that are approved for use on food. When diluted for ground application, the spray is 99% water.

What are the human health concerns of Btk?

Btk isn't considered toxic for people. It doesn't harm water supplies. Btk isn't considered a human pathogen. Human infections of Btk have been looked for but not seen in several large studies of people who lived in sprayed areas.

Many years of experience with Btk products have shown that the vast majority of people living in sprayed areas report no symptoms. A small number of people have reported symptoms including skin rash, irritation of the eyes, nose, and throat, and worsening of asthma or allergies after spraying. It isn't clear whether Btk was responsible for the symptoms or if the symptoms were related to disturbed dust and pollens or another component of the spray.

How do I minimize exposure to Btk?

Even though Btk has an excellent safety record, as a precaution, the Department of Health recommends that people in the spray area minimize their exposure by following these steps:

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

People who are more susceptible to infections or respiratory irritation should pay particular attention to these precautions. 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. People with concerns related to exposure to Btk, their health, or their immune system should contact their health care provider.

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