Gypsy Moth Treatments: NPV or Gypchek

​​​Nucleopolyhedrosis virus, or NPV, is a virus that occurs naturally wherever gypsy moth is present. It is the active ingredient in Gypchek, a biological pesticide product that we use on some sites. It is a powder made of gypsy moth caterpillars and virus particles that is mixed with a liquid containing starches, sugars and tree cellulose. It affects only gypsy moth caterpillars.

When gypsy moth caterpillars eat leaves coated with NPV, they stop eating and die in 7 to 14 days. We spray Gypchek only once in a season.

​When do you spray NPV?

We usually begin spraying NPV in southern Wisconsin in May and move northward, finishing in early June. Planes take off at sunrise. 

Why do planes spray s​o early in the day?

​We need the high humidity and low winds of early morning to assure the spray does not evaporate or blow away. The planes continue spraying as weather conditions allow, or until the area is finished. This may mean spraying into the late morning or afternoon, if possible.

Is NPV harmful to humans or animals?

Numerous laboratory and field studies over the past 30 years have shown that NPV presents no known risk to humans or animals.  

The low-flying planes may frighten pets or livestock, so we recommend that you keep them inside if possible.

If you are uncomfortable with the idea of spraying, please get on our list for updates of our plans so you can stay indoors or leave the area if you prefer:

Back​ to aerial spray program page