By Bill McNee, DNR Forest Health Specialist, Oshkosh; bill.mcnee@wisconsin.gov or 920-360-0942;
and Linda Williams, DNR Forest Health Specialist, Woodruff; linda.williams@wisconsin.gov or 920-360-0665
Examples of white “wool” coating on trees heavily infested with beech scale at Kohler-Andrae State Park (left) and in the Town of Beecher in Marinette County (right). / Photo Credit: Bill McNee (left) and Linda Williams (right), Wisconsin DNR.
Fourteen years after first detecting beech scale (Cryptococcus fagisuga, a non-native insect) in Door County, sites with high populations of beech scale have been found in additional counties. Beech scale is believed to have spread through the range of American beech in Wisconsin’s eastern counties, but until now has only been seen at low levels outside of Door County.
In April and May, high-scale populations were spotted at Kohler-Andrae State Park (Sheboygan County) and two sites in Marinette County. Beech scale was laboratory confirmed in both counties in 2010. But for an unknown reason, the scale population remained very low for more than a decade. It is unknown why the scale populations have increased dramatically in these locations but not in others.
At Kohler-Andrae State Park, an intensive survey of the beech trees found that the high-scale population was confined to two small pockets, totaling 13 beech trees on which scale was easily seen. Scale numbers on beech trees declined extremely rapidly away from these trees, and beech 15-20 feet away had few visible scale insects on them.
In Marinette County, two pockets have been located to date. One site is in the Town of Beecher, and one is in the Town of Silver Cliff. The beech trees in the Beecher stand consistently had high-scale populations. The scale population at the Silver Cliff site is high, but the extent of the infestation is unknown. Monitoring of these three sites will continue. In addition, field surveys of beech scale in eastern Wisconsin are scheduled this fall.
A map showing locations of known high beech scale populations in red (as of June 2023). High populations are known to be widespread in Door County. / Map Credit: Bill McNee, Wisconsin DNR.
When beech scale combines with Neonectria fungus, the beech bark disease complex is formed, killing many beech trees. The fungus typically arrives several years after the scale population becomes very high because the scale-feeding wounds are necessary for disease-causing fungi to enter the tree. Door County remains the only Wisconsin county where beech bark disease is known to occur and where extensive beech decline and mortality have resulted.
Landowners and managers outside of Door County who spot noticeable populations of beech scale similar to that shown in the above photos are encouraged to take a picture and report it to their DNR Forest Health Specialist. We are interested in knowing where the scale populations have increased because this will likely indicate a future appearance of beech bark disease in other counties for the first time.
Click this link for more information about beech bark disease.