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Maple Petiole Borer

May 23, 2006

The larva of this sawfly eats through the petiole of maple leaves 1/4 to 1/2 inch from the lamina. The ground becomes littered with leaves with short, ragged petiole stumps. The main part of the petiole stays on the tree for a time before dropping. Although the ground may become littered with many leaves, it is a small portion of the leaves on the tree, so there is little effect on the health or appearance of the tree. Control is not needed, which is good because little can be done. Raking up and destroying the petioles that drop later should remove many of the larvae. However, if there are many other maples nearby, adults are likely to fly in and attack the tree next spring anyway.

Eggs are laid in the spring into the petiole near its base, where it joins the twig. The egg hatches into a grublike larva that tunnels up the petiole. Near the leaf blade, the larva eats most of the way through the petiole, causing the petiole to weaken, turn brown and then black in that area. Wind may cause the petiole to break in the weakened area, causing the leaves to fall. The sawfly larva stays in the part attached to the twig. A few days later, the petiole drops; the larva leaves it, tunnels into the soil to pupate, and emerges the next spring. There is one generation per year.

Author: Phil Nixon


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