Woodpecker flecking on green ash and white ash, from birds feeding on emerald ash borer larvae, will often be extensive and very noticeable. / Photo Credit: Linda Williams, Wisconsin DNR

By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov or 920-360-0665

Ash trees that are flecked by woodpeckers will have the outer layers of their bark chipped off by the birds. Woodpeckers do this to punch through the remaining bark more easily to get at the tasty emerald ash borer (EAB) larvae living there.

Flecking usually starts at the top of the tree, providing a sure sign that insects are under the bark. Although the problem could be caused by ash bark beetles, the more common culprit is EAB.

EAB attacks all our native ash trees, but the amount of flecking and its visibility can vary between ash species. White and green ash will typically have more larvae under the bark than black ash, so larger areas of bark will be flecked off the white and green species.

Woodpecker flecking on black ash is less obvious than on green and white ash. Smaller areas and different bark structure makes it more difficult to spot the damage on black ash. / Photo Credit: Linda Williams, Wisconsin DNR

Researchers have shown that fewer EAB are required to kill a black ash compared to white and green ash, so there will be less flecking on black ash. Additionally, black ash bark looks very different than white and green ash bark, and flecking doesn’t show up as well.

EAB has now been identified in all 72 of Wisconsin’s counties, although the southern part of the state is more heavily infested than most northern counties. If you’re noticing flecking on ash for the first time on your property, you’ve dodged the bullet until now – but EAB has finally expanded into your property as we knew it eventually would.

Homeowners who want to protect just a few trees from EAB could consider treating ash trees with insecticide in the spring. Insecticide treatment is most successful if started when woodpecker flecking and decline are minimal. Treatments need to be done as long as you want to keep the tree alive. Treatments that homeowners can buy themselves require retreating each year; some products available to professionals last longer between treatments.

Woodpeckers that strip away bark to feed on emerald ash borer larvae usually start working in the tops of ash trees. Initially, flecking will be light. / Photo Credit: Linda Williams, Wisconsin DNR

Treatment with insecticide is generally not practical for woodlot owners. They should consult with a Wisconsin Department of Natural Resources forester or consulting forester for management advice or read through the Wisconsin EAB Silviculture Guidelines.

Visit the DNR EAB webpage for more information.