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

The spiny oak sawfly feasts again. While defoliation by this insect is common in understory oaks, this year, lower branches of overstory oaks have also seen damage. All damage so far has been observed on red oaks. Previously we saw a widespread outbreak in 2005 with lesser reports of damage in 2007, 2016, 2017 and 2021.

Spiny oak sawfly larvae. Photo: Wisconsin DNR

These larvae are not large but often feed in groups with several on a single leaf. They feed on the undersides of leaves, eating the leaf material but leaving many of the veins.

These sawflies feed until late June or early July. By the time you notice the damage, the larvae are often done or nearly done feeding on the leaves, so make sure the larvae are present before deciding to spray for control. Since the larvae feed on the undersides of leaves, finding a spray that works well can be difficult.