There have been numerous reports thus far this season of damage to trees and shrubs attributed to the deep diving temperatures that occurred in December during Christmas week. However, wilted, darkened buckeye (Aesculus glabra) leaves appearing randomly among healthy leaves isn’t winter injury; it’s the handiwork of the Buckeye Petiole Borer (Zeiraphera claypoleana, family Tortricidae).
During last week’s BYGL Zoom Inservice, Pam Bennett (OSU Extension, Clark County) reported that borer damage to buckeyes is apparent around Springfield, OH, and I took pictures yesterday of the damage in Butler County. The hit-or-miss nature of the leaf-wilt damage is the calling card of the borer.
We’ve noted in past BYGL Alerts that the moth appears to prefer small understory trees growing in wooded areas along streams. I’ve rarely seen damage on mature trees or trees in landscapes. The literature notes this native moth is specific to Ohio buckeye (A. glabra); however, petiole borer activity has also been observed on yellow buckeye (A. flava). Whether or not it’s the same moth species has not been determined.
Detection
As their common name indicates, the moth caterpillars tunnel within leaf petioles to feed on vascular tissues. The damage causes leaves to rapidly droop, wilt, and turn dark green to black.
While single-leaf symptoms may mimic freeze/frost injury, the random distribution of symptomatic leaves among healthy leaves excludes a weather-related diagnosis. Damaged leaves eventually detach producing mild defoliation.
I’ve never found more than one caterpillar per petiole even where populations are high. A small hole exuding granular-like frass (insect excrement) indicates there is a caterpillar actively feeding within the petiole.
A clean hole in the petiole indicates the caterpillar has completed its development and has exited to pupate in the soil. Slicing open the petiole will reveal a short, empty chamber.
Trees usually only suffer a few damaged leaves. Although the damage may appear conspicuous, the caterpillars seldom cause enough leaf loss to affect the overall health of infested trees.
On the other hand, the caterpillars may occasionally bore into the tender new terminal growth on small understory trees. I reported this observation in a BYGL Alert two years ago because I’ve never found this type of damage reported in the literature. Such damage to the main stems of small trees represents a potentially more serious impact compared to the loss of a nominal number of leaves to petiole boring activity.
The moth has two generations in Ohio. Caterpillar development occurs quickly during the first generation and is coming to an end in the southwest part of the state.
Management
There are no chemical control recommendations given that the damage is usually confined to wild buckeyes growing in wood lots and leaf loss from the petiole borer is seldom significant. However, I've seen localized populations gradually increase over successive years to eventually produce very noticeable symptoms with the damage caused by the second generation becoming more severe.
A two-step management program can be applied to reduce localized petiole borer populations. The first step is to make certain the petioles actually contain caterpillars; a clean hole means the caterpillar has vacated the premises. Removing first-generation caterpillars will decrease the damage caused by the second generation later this spring and the removal of second-generation caterpillars will help to deplete the overall population.
The second step is to destroy the caterpillar within the infested leaves and stomping is highly effective. Thus far, no populations have become resistant to this control method.
