By Bill McNee, DNR Forest Health Specialist, Oshkosh;
Bill.McNee@wisconsin.gov or 920-360-0942
A tree shows high numbers of spongy moth caterpillars, though the majority of the caterpillars have been killed either by virus (hanging in an inverted V) or fungus (hanging in a stretched line, head down). The virus and fungus helped to quell a potential outbreak in many areas of the state in 2024. / Photo Credit: Bill McNee, Wisconsin DNR
As the 2023 spongy moth season ended, there were hopes for a return to colder and wetter conditions in 2024 so that the spongy moth outbreak would decline or even come to an end.
What wound up happening in Wisconsin was the “lost winter,” the warmest since recordkeeping began in 1895. Given this warmth, there were concerns that the widespread spongy moth outbreak would continue for a third consecutive summer, with good caterpillar survival, ongoing defoliation and high rates of tree mortality in already stressed forests.
Date: Feb. 16-18, 2025
‘Winter burn’ refers to a type of damage to evergreen foliage that typically occurs over winter. Common symptoms are browning and dying from the tips of the foliage inward. Several factors cause winter burn on evergreens, including winter ‘thaws’ while the ground is frozen, dry soil in autumn, a long period of very cold temperatures, winter sun on evergreen foliage or drying winter winds, poor siting of susceptible plants, recent planting/transplanting and the individual plant’s susceptibility. Frequently affected plants include yews, junipers, boxwood, arborvitae, rhododendrons, dwarf Alberta spruce and hemlock. 
*These training opportunities are provided as an information service only and does not constitute an endorsement from the WI DNR.