Why Are Lots of New Leaves on a Maple Tree Falling & Covering the Lawn?

Identification

• Maple trees are susceptible to maple petiole borer, a small, wasp-like sawfly that overwinters in the soil as pupae. The adults that emerge in spring start to lay eggs in the petioles or leaf stems. Though the pest strikes all maple varieties, sugar maples are especially prone.

Damage

• The 1/3-inch long pest larvae with brown heads feed on leaf petioles as soon as they hatch, severing connective tissues. This causes the still green leaves to fall suddenly. The damaged petioles are black. This is indicative of pest presence. The larvae fall onto the ground with damaged petioles and pupate in soil.

Control

• Though the sudden loss of green leaves is troubling, trees usually lose just 10 percent of their foliage. The pests rarely cause serious threat to tree health. The use of insecticides is not effective, as adult borers fly in from other areas and lay eggs.