Our office has noticed a recent uptick in the number of homeowners concerned about their oak trees. At first, we simply attributed these calls to the hot summer temperatures and sporadic rains, but as our arborists visited more and more properties and reported back similar findings, we realized that what is happening in our region is a particularly broad infestation of leafminer.
What we are seeing is Solitary oak leafminer. This is a very small species of moth that lays its eggs on the leaf and once hatched the larvae start to feed on the tissue between the top and bottom layers of the leaf. Typically the damage of this insect is non-life threatening to the tree. Though the trees may look very striking (sometimes up to half the tree appearing discolored) the damage from a single season is usually minimal to the tree. However multiple years of defoliation can lead to decline and secondary infections.
This insect can infest several species of oak but prefers white oak. The insect itself is quite small as larvae go, with mature larvae only measuring about ¼ inch long. Identification of this pest is usually after the damage to the host has already happened. The damage will start as small blotchy discolorations on the leaves which quickly turn to bronze/brown as the tissue dies. Heavy infestations may lead to premature leaf drop. Carefully peeling the topmost layer of the leaf will reveal either the active larvae or their cocoon.
There are steps that you can take to make sure that your trees are healthy and have the best chance of having little impact from leafminers. The best thing that you can do is to make sure that the tree has ideal growing conditions. Providing resources to your tree through soil care helps your trees to defend themselves against common pests and infections. It is important to discuss with your arborist appropriate action if you notice evidence of leafminer on your oak trees.
If you notice that your trees are showing signs of leafminer, please give your arborist a call so that they can help create a proactive plan to provide a long healthy life for your trees.