Sunday, June 12, 2022

White Oak Leaf Damage


Questions abound this spring about visible damage to oak leaves, particularly to white oaks, one of our most abundant species in north Georgia. Some trees are so damaged they look like they’ve been sprayed with herbicide. Facebook groups and local extension offices have fielded numerous inquiries about what is happening to the trees and what homeowners should do about it. My trees are similarly infected so I decided to look more closely at what was happening.

White oak (Quercus alba) in my yard showing damage

I won’t take credit for determining that the source of the damage is the solitary oak leafminer. Other folks had already provided links to articles and photos of this moth’s lifecycle. My goal was to confirm that it was this moth’s larvae inside the leaves. I had heard that the insect was feeding inside the layers of the leaf, so I used a pair of sharp sewing scissors and my 10x hand lens to get a look.

The small oak leafminer caterpillar

It was clear, for the most part, that the damage only affects the upper tissue layer; the back of the leaf was fully intact. The tiny caterpillar, no bigger than a grain of rice, was feeding on the leaf’s tissue amidst a collection of frass (its own poop). Several of them had formed clear enclosures; these are the cocoons in which the larvae will transform to the tiny moth (microlepidoptera) it becomes.

Forming cocoon
Cocoon completed

The bottom line is that this damage is perfectly natural, doesn’t hurt the trees, is mostly likely short-term, and certainly doesn’t require any chemical responses. While some folks recommend discarding the fallen leaves (to remove the unhatched cocoons), keep in mind that trees all around you will still contribute to the next generation. These kinds of irruptions are normal in nature and will balance themselves.

1 comment:

  1. Also keep in mind that the natural bugs living on our native species are the food supply to our birds! The non-native plants (generally untouched by insects) provide nothing to the food chain for that reason. Many birds need insect protein for their young, even if as adults they are mostly seed eaters.