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Locust Leaf Minor

BLACK LOCUST LEAF MINOR
By Ken Mays 1992 Newsletter

As you travel the beltway during these late summer months you probably have noticed a lot of the trees along the roadside turning brown. The trees are “Black Locust” (Robina pseudoacacia), similar to the ornamental “Honey Locust” in appearance but is undesirable to have in home landscape. The Black Locust is generally found growing wild along woodlines, has prickly thorns and is classified as a weed tree. The locust leaf minor (Xenochalepus dorsalis) is the insect causing the browning and drying out of their leaves. The minor is a small beetle that, while in its larval stage, eats into the inner layer of leaf tissue forming a mine or hollowed out area between the leaf’s layers. This mined area then dries out causing the brown appearance typically seen this time of year. When the larva matures into a small beetle, it emerges and feeds on the remaining portion of the leaf causing total deterioration. The black locust is a durable tree, known for its ability to survive direct lightning strikes, attacking black snakes and bouncing back after annual defoliation from the leaf minor when any other tree would have died after two successive years of such a brutal attack!

This is one of many different kinds of leaf minors and it too can be controlled. The key to minimizing damage is to spray the trees in May while the minor is still in its larval stage and then in July during the beetle stage with products such as Orthene, Merit or Sevin to name a few.