Sawflies Feeding on Oaks
Oaks have hundreds of herbivores so it is no wonder that towards the end of summer some of the leaves show all types of feeding damage. Last week I found many trees with leaves that had damage called ‘window paning’.
This type of damage occurs when a small herbivore feeds on the lower surface of a leaf but leaves a thin layer of the upper surface intact. Thus, if you hold the leaf up to light you can see through it, mostly. The remaining layer of leaf quickly turns brown. Lots of this feeding can make trees look tattered.
Right now some of this damage is from the scarlet oak sawfly, Caliroa quercuscoccineae. Sawfly larvae, like hibiscus sawflies, birch sawflies, and some rose sawflies, often look like caterpillars even though they are actually wasp larvae. This species and many others look more like slugs. Generally these do not cause major defoliation in landscape trees or street trees and do not need management. It is just nice to be able to explain some of the browning and minor damage folks may be seeing.