Caterpillars begin to emerge
Depending on the temperature, spongy moth (Lymantria dispar) caterpillars start emerging in late April through mid-May in Wisconsin. Sticky barrier bands should be up by the first week of May. Directions on how to make a sticky barrier band. Monitor these each day and sweep caterpillars trapped below the barrier band into a bucket of soapy water. Recently, similar sticky-band trapping methods (for the invasive spotted lanternfly) have caused concerns for birds in Pennsylvania and other mid-Atlantic states. To help reduce risks to birds, consider placing chickenwire or mesh screening over the sticky bands to prevent birds from contacting the sticky surface. See this page for additional info about preventing bird contact.
Two important notes about sticky barriers: 1) be aware that trees with deep furrows in the bark allow caterpillars to sneak behind the barrier band and hide. 2) Do not put the sticky material directly on your tree. Insecticides may also be used to help control spongy moth caterpillars at this time of year.
Remove sticky barriers in late May as these barriers are not as effective against larger caterpillars.
Aerial spray treatments to suppress outbreaks or slow the spread of spongy moth occur in mid to late May when caterpillars are very small and vulnerable to the bacterial insecticide Bacillus thuringiensis kurstaki (Btk). Maps of treatment areas are available online at the Wisconsin Spongy Moth portal website. Treatment schedules are dependent on weather. Daily updates are available by phone at: 1-800-642-6684.