Noticing your locust tree has a lot of brown leaves on it? Furthermore, have you noticed that just about every locust has a lot of brown leaves? It’s being caused by the mimosa webworm. This non-native insect is a common pest of honey locusts, but luckily, most trees have plenty of green, healthy leaves, and this late in the growing season, we are less concerned about defoliation.
The female mimosa webworm moth lays clusters of eggs, and the caterpillars weave leaves together and feed inside. They don’t completely consume the leaf like many caterpillars do; instead, they feed on and skeletonize the leaflets, which eventually turn brown.
Damage is seldom serious to otherwise healthy, well-established locust trees, and treatment is rarely warranted. It is also too late this year to apply any treatments. For younger trees with fewer leaves, the damage can be a source of stress, but again, it is late in the growing season, and the leaves would be falling soon anyway.
For young trees, you can help by reducing other sources of stress. Remove turfgrass or other competing plants from around the base of the tree and mulch the soil to prevent grass from growing back and to moderate soil temperature and moisture.
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