Maple Trees Losing Their Leaves

Kalamazoo, Mich.- Does it seem like autumn under your maple tree with the exception that the leaves are green?

Last week I began to notice green leaves under maple trees. Upon closer observation, the leaves had only half of the stem (petiole). This is caused by tiny larvae called the maple petiole borer which is in the same group of insects as the sawfly.

The female slices a small slit into the plant stem and inserts an egg. The egg hatches into a small larva that feeds inside the petiole, weakening it and causing it to break off and falls to the ground. There is only a one generation in Michigan and it usually only lasts about one to two weeks. Maple trees have a very dense canopy and most trees can sustain the leaf loss and does not cause harm to the tree.

We recommend no chemical application for maple petiole bore since there are many natural biological control agents that keep this pest population in check. The recommendation is to clear the leaves by either raking or mulching while mowing the lawn.

The actual bore remains in the portion of the petiole that is still attached to the tree and in a vulnerable location for the biological control agents to seek out and kill.

For more information about MSU Extension Horticulture programs, call Jeanne Himmelein, District Horticulture Educator at the Kalamazoo County MSU Extension office, (269) 384-8010, or visit our web site at www.kalcounty.com/msue

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