Department of Agriculture, Trade and Consumer Protection

The Wisconsin Department of Agricu​lture, Trade and Cons​u​mer Protec​tion uses aerial spraying every spring and summer, mainly in western Wisconsin to slow the s​pread of spongy moth​ (Lymantria dispar​) in non-quarantined counties as part of the National Slow the Spread program. We spray to kill spongy moth caterpillars in May and early June. In la​te June and July, the U.S. Department of Agriculture Forest Service applies mating disruptors by spraying via a plan​e to p​revent the adult moths from mating.​​​

If your home is in or near a spray site, you should receive a postcard in late​ April to early May telling you about the spraying and providing you with contact information if you have questions. We cannot tell you ex​actly what days we will be spraying in your area, because we time spraying according to when spongy moth caterpillars hatch and when weather conditions are right. We also notify your local media, airports, schools, health departments, and law enforcement.

You can get up-to-date information on spray plans daily during the spray season:

Products

We spray several different products, depending on location and life stage of the moth:

• Bacillus thuringiensis kurstaki (Btk)​
• Mating Disruptions ​​
  

Spray Operations​

We plot spray areas using GIS, and the spray planes are outfitted with GPS equipment to accurately target the spray areas. We monitor their progress on computer screens in real time with a display that shows where they are and whether they are spraying the product or have shut it off.

The planes are aiming for the tree tops where the caterpillars are feeding, so they must fly very low. They are small planes, but are fairly loud because they do fly so low. 

We usually spray in the morning when high humidity and low winds assure that the product does not evaporate or blow off the site. If weather conditions permit and work remains to be done, planes will fly later into the day. Because they are weather dependent, spray plans may change at the last minute.

Spray Area Selection 

We set traps during the summer to catch adult moths and conduct egg mass surveys in the fall, visiting areas where we have trapped high numbers of adults to look for egg masses that will hatch in the spring. Using this data, and comparing it with previous year's results and our knowledge of factors that affect the spread of spongy moth, we prioritize the sites that pose the greatest risk of spreading.

Aerial Applicator

Businesses that apply pesticides by aerial application are licensed by the state of Wisconsin. The companies that are awarded the spray contracts meet all of the requirements of Wisconsin and the U.S. Environmental Protection Agency. 

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