Ever walk into the yard in late spring to be confronted with a large number of otherwise healthy looking maple leaves covering your grass? Well, the odds are good that this is the work of a tiny insect called the maple petiole borer. The petiole is the stem of the leaf and the larvae of this critter does its work by eating inside this stem.

The insect is a sawfly which deposits its eggs near the base of the leaf petiole in the early spring just as the foliage emerges from the buds. When the eggs hatch, the tiny larvae begin to feed inside the petiole. By the time they are done feeding and ready to pupate, they have hollowed out the leaf stem. It is so weakened that it will drop off in the breeze leaving a darkened area at the point of separation.

As mentioned previously, the key symptom is the dropping of a relatively large number of otherwise healthy looking leaves. The black area where the petiole breaks is also a strong symptom. If you take a close look at the petiole, you will find that it is hollow.

A somewhat long shot method for preventing or minimizing this problem would be to persistently clean up and destroy all the leaves as they fall to the ground. The larvae will usually crawl into the ground in order to complete the next step in their life cycle. Preventing them from doing so, MAY help to minimize next year's crop of petiole borers.

Even in severe cases, maple petiole borer causes little damage to an otherwise healthy tree. Most trees have the ability to replace lost foliage early in the season so this problem is mostly one of aesthetics.

Even if you wanted to treat for this problem, it would be quite difficult. The insecticide would have to be on the petiole pretty much the day that the leaf opened. Once he eggs are inside, most insecticides would be ineffective. So...just rake up the leaves and put them in your compost bin. The tree will be just fine...unless it has other, more serious problems.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Types of Insects

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