By Bill McNee, Forest Health Specialist, Oshkosh
bill.mcnee@wisconsin.gov or 920-360-0942
Mature spongy moth caterpillar on a leaf. Photo: Bill McNee, Wisconsin DNR
Wisconsin Department of Natural Resources Forest Health staff are cautioning Wisconsin residents that the next two months could bring the worst spongy moth outbreak in more than a decade.
The caterpillars of this invasive insect prefer to feed on oak, birch, crabapple, aspen and willow leaves, but will also feed on many other tree and shrub species.
Southern Wisconsin and parts of the north are already in a high-population outbreak that is predicted to continue and spread. Populations have remained high due to a low incidence of caterpillar-killing diseases last summer. In addition, weather conditions in 2023 are favorable for the caterpillars and unfavorable for Entomophaga maimaiga, a fungus that kills spongy moth caterpillars.
Property owners are encouraged to examine their trees and take action. Specifically:
It’s a different case in northern Wisconsin, with green up just beginning and fire season at its peak. In fact, the areas with sandy soil and an abundance of pine trees are at critical fire danger, particularly because of a phenomenon called the “spring dip” – a time when the moisture content of pine needles is low and starch content is high. When pines are in the spring dip, individual tree torching and crown fire in groups of trees is a very real possibility. This type of fire is the most challenging to contain and extinguish.
As there is every glorious spring, there has been a flurry of tree planting in Wisconsin. Each little tree, from seed to sapling, is a hope and prayer that we make for the future. But as each reader knows, that future might be many years away.
On April 20, the First Downs for Trees program celebrated its 13th year by distributing 403 trees to 16 Brown County communities for planting. First Downs for Trees is a cooperative effort between the Wisconsin Department of Natural Resources (DNR), the Green Bay Packers, Wisconsin Public Service (WPS) and corporate sponsors Essity and Green Bay Packaging, Inc.