Aphids & Ash Trees

Hundreds of species of aphids exist, and they are among the most common pests to infest trees, ornamental plants, flowers and vegetables. One adult aphid can produce 80 offspring in just one week, so it's important to deal with aphids as soon as you notice them. Aphids can cause unsightly damage to ash trees (Fraxinus spp.), though they usually don't kill the tree. Fortunately, aphids are almost always easy to control and eradicate from your ash trees.


Aphids are small insects that use their sucking mouth parts to feed on the foliage of trees and plants. Depending on the species, aphids can be a range of colors, including brown, yellow, white and black. Aphids measure about 1/10 inch long, making it hard to see a single aphid on a plant. Typically, aphids feed in colonies, making them easier to notice on the leaves and foliage of a tree. They tend to feed on the underside of leaves.


Aphids take up residence in the tips of new plant growth or on the undersides of leaves to feed on the tree. The pests feed by piercing the foliage and leaves with their long mouth parts and sucking sap and moisture from the tree. Over time, the leaves begin to turn yellow and become misshapen. Aphids also leave honeydew, a sticky substance excreted as they feed, on the surface of the leaves. The honeydew can cause black mold to grow on the leaves. The ash leaf curl aphid feeds on ash trees and causes the leaves to become curled, puckered and twisted.

Biological and Cultural Control

While aphids don't usually cause devastating damage, controlling them will prevent the leaves of an ash tree from becoming unsightly. Direct a strong stream of water from your garden hose on the tree. The water will knock the aphids from the leaves and will also help rinse the sticky honeydew from the foliage. Natural enemies, such as parasitic wasps, lacewings and ladybugs, feed on aphids and can help control an infestation in an ash tree. Pull weeds from around the tree because certain varieties attract aphids. Reflective mulch applied around the trees might also deter aphids from feeding on the foliage.

Chemical Control

Insecticidal soap and horticultural oil are effective ways to control an infestation of aphids. Spray the products on the entire surface of the leaves, including the undersides, to destroy the aphids. These are usually only temporary control measures, however. Because aphids usually don't cause enough damage to destroy an ash tree, pesticides aren't usually recommended, though certain types target aphids.

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