The Summer Olympics may be over, but there is one more bronze to give out. In parts of western N.C., hillsides covered in black locust trees are turning bronze. Despite the remaining summer temperatures, it looks like early fall color across the landscape. While the thought of early temperatures may bring hope to some, this dramatic transformation is actually caused by a common insect, the locust leafminer.The locust leafminer is a beetle that feeds primarily on black locust trees. When they are immature beetle larvae, they “mine” the leaves, meaning they feed on the soft tissues between the upper and lower epidermal layers of the leaf, creating a tunnel in the leaf. As adults, they consume all but the veins of the leaf. This is called “skeletonization” and gives the leaves a lace-like appearance. Feeding damage will cause the leaves to turn brown, bronze or gray, and often in late summer, entire hillsides become discolored, drawing a lot of attention.
While the damage itself is quite eye-catching, in most cases it does not affect the long-term health of the tree. Natural enemies of the locust leafminer tend to help manage outbreaks, so intervention is rarely warranted. In some cases, however, when trees are already stressed or weakened, or trees are attacked by the leafminer year after year, growth loss or mortality may occur.
So these beetles may have given false hope for early cool temperatures, but they’re still right around the corner!