Ag Alert! Oak Shothole Leafminer Outbreak

Oak shothole leafminer has caused significant damage to oak trees in several counties in West  Virginia this summer. It also has been reported to be in a few other states, including Massachusetts, Rhode Island, New Hampshire, New York, Pennsylvania and Ohio. Oak shothole leafminer is an insect that  belongs to the order Diptera and is native to the United States. However, its biology and damage to oak trees have not been widely studied.

Larval and adult stages of oak shothole leafminer feed on oak leaves. Larvae tunnel through the leaf tissue, leaving telltale trails. This damage is known as blotch mines. 

In contrast, female adults create leaf holes, which are characteristic of this fly species. Because the mouth parts of oak shothole leafminer females cannot penetrate leaf tissue, they use their ovipositors to cause enough damage so that any fluids leaking from the leaf can then be lapped up. The area injured by this action soon turns brown and dries, eventually forming a small disk. These disks of necrotic tissue often remain conspicuously attached to the expanding hole formed in the leaf.  

In West Virginia, oak shothole leafminer has been observed on black oak, chinquapin oak, chestnut oak, white oak and northern red oak. Oak shothole leafminer damage can reduce photosynthesis so much that it stops the season’s growth for oak seedlings. On full-grown trees, oak shothole leafminer causes only aesthetic damage, but if damage persists for multiple years, it is possible that oak trees might show more severe injury symptoms. In general, it should not be a concern for older trees, and the problem may not recur in coming years. 

If you see oak shothole leafminer damage, contact one of the specialists below to help us better understand how widespread the problem is in West Virginia. 

This alert impacts all West Virginia counties.