Please be on the lookout for signs of Shothole Leafminer Fly damage to New Jersey Oak Trees.
The oak shothole leafminer, Japanagromyza viridula, is a very small fly that emerges in early spring to feed on oak leaf buds and very young leaves. It is a native insect that has natural predators to help control outbreak populations, however, recently damage from this fly has become more prevalent in the Northeast. Please help track the shothole leafminder fly in New Jersey by sending a picture of leaf damage (can be on green leaves or on fallen brown leaves), along with the County where the picture was taken to our forest health program at email@example.com
Description and Biology
The oak shothole leafminer, Japanagromyza viridula, is a very small fly that emerges in early spring to feed on oak leaf buds and very young leaves. They feed by piercing the buds with their ovipositors (literally "egg placers") and lapping plant juice. As the buds break and new leaves expand, a tiny hole forms at the ovipostion injury site. The holes get bigger (up to 3/8 inch) as the leaves grow. Females eventually pierce leaves to lay eggs inside. Tiny maggots hatch and excavate blotch mines as they mature. Once mature, usually by the end of May, maggots leave their mines and drop to the soil where they pupate and spend the rest of the summer and the winter. Active mines are light green to tan but darken once they're abandoned. The damaged tissue eventually drops away leaving large, ragged holes. Female feeding holes and the leaf mines remain throughout the rest of the growing season. We have one generation per year in North Carolina.
Oak shothole leafminers often leave symmetrical holes in new oak leaves.
Oak shothole leafminer damage can sometimes be quite spectacular.
Black oak, burr oak, Chinese chestnut, post oak, red oak, sand post oak, scrub oak, turkey oak, and white oak have all been reported as hosts of the oak shothole leafminer.
Oak shothole leafminers infest most species of oaks in North Carolina.
Like most leafminers in this family, oak shothole leafminers have numerous parasites. Next year the infestation may not even be noticeable because of the parasites. Usually by the time the damage is noticed, the leafminers have already abandoned the mines. Applying a pesticide during the growing season will not help improve the appearance of an infested tree. It is probably better not to try to control these leaminers with pesticides.
Oviposition damage by oak shothole leafminers persists long after the maggots have left the leaves.
Publication date: July 7, 2020