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When Encountering A Rain Of Wooly Aphids

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Mario Villarino, DVM, Ph.D., Hopkins County Extension Agent

By Dr. Mario Villarino, Extension Agent, Ag./Natural Resources, Hopkins County, [email protected]

As we were walking away from the Hopkins County Courthouse earlier today after our Commissioner’s Court interpretation, we ran into a “rain” of woolly aphids just as we tried to get into our vehicle.

A common name for woolly alder aphid (Prociphilus tessellatus) is the maple blight aphid because of the dense, white, woolly masses it produces on the leaves and twigs of its primary host, silver maple (and occasionally red maple). The aphids on the trees are wingless, plump, gray, and concealed beneath their own dense, white, waxy strands. These feed on sap from the maple trees from the time of bud-break until late June. Then, winged adults, some with abdomens covered in white fluffy wax, are produced in the colonies. These winged migrants readily fly when disturbed and create the illusion of tiny masses of cotton floating through the air.

These aphids are leaving the maple trees and flying to alders, where they will establish new colonies on the secondary host. Woolly alder aphids require both alder and maple trees to complete their life cycle.

They are similar to true aphids, but have white waxy strands covering their pear-shaped bodies. The wax filaments make these aphids look fluffy and cottony, as if they are covered with wool. The wax also keeps predators away from these aphids and helps them move easily around plant hairs. In most cases, management is not necessary for the health of trees and shrubs, especially large mature plants.

Similar to other aphids, natural enemies (lacewings, lady beetles, hover flies and parasitic wasps) help keep woolly aphid numbers low. Woolly aphids are not affected by horticultural oils and soaps, like other aphids. This is because the waxy secretions of the woolly aphids and the distorted leaves do not allow the pesticide to enter the leaves. Contact pesticides, like permethrin, also do not work on woolly aphids for the same reason.

In cases where management is necessary to protect plants, systemic pesticides, like imidacloprid and dinotefuran, are the most effective against woolly aphids. However, imidacloprid and dinotefuran are very toxic to pollinators. Either avoid applying these insecticides to bee attractive plants or wait until the plants have finished blooming before treating them.

For more information about this or any other agricultural topic please contact the Hopkins County Extension Office at 903-885-3443 or email me at [email protected].

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Author: Faith Huffman

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