Below will address questions regarding the spongy moth caterpillar spraying operation on the west side of Madison.

If you have additional questions, please contact the Urban Forestry office at forestry@cityofmadison.com or call at 608-266-4816.

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what is happening and When?

Two areas on the west side, the southern portion of the Glen Oak Hills Park and the Kenosha Greenway will be treated with a spray to protect these public trees from the spongy moth caterpillar. The spray will be applied from the ground into the tree canopy by certified arborists. 

The tentative dates for the application is now Friday, May 10. 

This page will be updated should caterpillar development, tree growth, or weather cause delays to the start of the spraying operation.

Expect to encounter temporary closures of North and South Kenosha Drive during the spraying operation.  This is for the safety of the arborists performing the work.  More details can be found in the temporary road closure section.

These areas were found to have a high concentration of egg masses in 2023, so they were identified as areas that could see another spike in the population in 2024 if environmental conditions favored another spike.

The spray dates are tentative because you have to wait for the right time to apply it where it lands on leaves, and also the caterpillars are in a young enough stage where they will ingest it.  You also need to wait for a period when there is little chance of rain so the spray is not immediately washed off the leaves the caterpillars are eating..

Spray Delay Timeline

It was previously stated on this website that the tentative dates were April 25 & 26. 

The spray date was pushed back to May 1 & 2 based on observations regarding spongy moth caterpillar hatching.

However, the May 1 & 2 date was cancelled due to weather forecasts calling for rain.  The spray must sit on leaves to be effective and rain would just wash it off.  A new spray date of May 3 was selected.

May 3 date was cancelled due to leaf development. The spray needs to land on leaves and be present for the caterpillars to eat.  Based on observations of the spray area, and general advice from forest health specialists in the Wisconsin DNR, it is best to wait until the trees produce more leaves to be more effective.  A new date of May 8 was selected.

The May 8 spray date has been cancelled due to rain in the forecast for this date.

The new hopeful spray date is Friday, May 10.

why are these areas being sprayed?

The spongy moth caterpillar defoliates trees. This is not lethal to trees by itself, but it is a stressor for them as they try to regrow them.  All of the energy spent to grow more leaves makes them more prone to disease and pests - especially during dry and drought conditions.  This stacking of stressors can lead to tree loss.

These trees are being sprayed to stop the spongy moth caterpillars from destroying the leaves, and keep the trees safe.

 

Map of the areas to be sprayed

The below map shows the approximate area where the spraying will occur in the Glen Oak Hills Park and the Kenosha Greenway.

Map showing areas of the southern portion of the Glen Oak Hills park and the Kenosha Greenway shaded in red. This signifies they will be part of the spongy moth spraying effort.

 

What is in the spray and how does it work?

The technical name for the bacteria is Bacillus thuringiensis kurstaki (Btk).

Btk affects the ability of the spongy moth caterpillar to digest, eventually killing them.

 

Safety of the spray for people, pets, and pollinators

Btk has not been shown to be harmful to people, birds, pets or pollinators, like bees or species of butterflies native to Madison.  Also, by targeting the application at this time of year, it will limit any possible harmful effects to other insects that may ingest the bacterium.

 

More information about btk

Wisconsin Department of Agriculture, Trade, and Consumer Protection: Spongy Moth Treatments: Bacillus thuringiensis kurstaki

Wisconsin Department of Agriculture, Trade, and Consumer Protection: Btk Treatment Fact Sheet

 

Neighborhood notification letter

Notification letter that will be sent to residents near the application area can be found here. 

The tentative dates for the application is now Friday, May 10.

This page will be updated should caterpillar development, tree growth, or weather cause further delays.

The spraying has been delayed multiple times since initially scheduled.  You will notice on the letter it gives a date in April for the application date. You can read a timeline for the causes of the delays here.

 

temporary road closures

In order to spray into the canopy of the trees, the certified arborists hired by the City will be using lift trucks. 

For the safety of the arborists, S. Kenosha Drive and N. Kenosha Drive are highly likely to be temporarily closed at times during the spraying operation.

The trucks may need to be parked in a way that may block traffic. 

We would not want anyone driving through to bump into these vehicles while it is holding of the arborists several feet in the air working to protect the trees.

 

why are only these two areas being sprayed and not all of Madison?

There are two main reasons.  1) The concentration of spongy moths seen here and 2) the equipment.

 

Concentration

This area saw a very high concentration of spongy moths in 2023.

If weather conditions are favorable for the spongy moth again this spring, then we could have another population boom of the pest in 2024.  And that means the trees here could be defoliated again like last year, which we want to avoid.

The concentration of egg masses here was quite high in this area compared to previous years and also compared to the rest of Madison.  There were spongy moths in other areas, but not in the same level of concentration as what was observed in this area.

In 2023, the Engineering Division asked for help from residents to report areas where spongy moth was spotted.  Staff from Engineering was able to use help from residents to zero in on this particular heavily wooded area with many oak trees as a place that had an especially high concentration of spongy moths.

The best course of action when treating spongy moth is to seek out these areas of highest concentration where they can do the most damage, and work to treat that area to minimize their threat to protect the trees. 

Equipment

The other important factor is the equipment.

The specialized truck with high-pressurized tanks that can spray Btk from the ground has limited range. 

The Kenosha Greenway and the southern portion of the Glen Oak Hills Park allows for this special equipment to be deployed since it is narrow and close to the road where the lift trucks with the high-pressure tanks can be used.

Other public lands that are equally heavily wooded as the Kenosha Greenway and the Glen Oak Hills Park are not accessible by this equipment.