Caulocampus acericaulis

While on a walkabout in Winton Woods (Great Parks, Hamilton County) earlier this week, I came across a Black Maple (Acer nigrum) with new shoots and leaves that were wilted and blackened. The black maple was at the edge of a forest and had not been planted.

The leaf-shedding handiwork of the Maple Petiole Borer (Caulocampus acericaulis, family Tenthredinidae) is becoming evident in southwest Ohio. This non-native sawfly was introduced into the United States from Europe. Although the sawfly prefers sugar maples (Acer saccharum), other maples may occasionally be infested.

The annual leaf drop on sugar maples caused by the maple petiole borer (Caulocampus acericaulis) is underway in southwest Ohio. To separate leaf drop by the petiole borer rather than high winds or anthracnose, look for abnormally short petioles on the fallen leaves and for broken petioles that remain attached in the canopy.

Reports of maples dropping green leaves are on the rise in southwest Ohio. They are not being shed because of maple anthracnose which usually happens a bit later in the season.

Finding large numbers of green leaves littering the ground beneath maple trees wouldn't be a surprise given the recent high winds and heavy rains over much of Ohio. However, you should take a second look at this time of the year for short petioles on the shed leaves and broken petioles remaining attached to the tree. Both are tell-tale symptoms of the maple petiole borer.