Got Aphids? Probably.

This spring, if your trees have leaves, they probably have aphids too. Roses, columbine, ash, aspen, honeysuckle, maple, spirea, fruit trees, pines and spruce are all likely candidates for aphid infestation, just to name a few.

Aphids come in many colors and sizes. Always less than ¼ inch in size, opaque, green, brown, and gray aphids are found on the under side of leaves. In the case of conifers, they are found along and at the base of the needles.

Why are aphids so numerous this year? Some of the possible causes are:
1. Our mild winter allowed for overwintering eggs and adults to survive.
2. Our warm and early spring fostered early insect infestations.
3. April precipitation resulted in lush and early plant foliage.

Aphids prefer plant material with succulent growth and high sugar content. The early growth, along with the April rains produced this. Our subsequent dry weather decreased the amount of water in the plants – concentrating the sugars (photosynthate) in the foliage. The result: a banquet for aphids! Normally just a nuisance, an aphid infestation can lead to problems. If severe infestations are encountered, loss of vigor to the plant will occur. Aphids can also cause leaf discoloration, distortion, stunting and drop. This spring, many infestations will require treatment.

Some telltale signs of infestation include ants, bees, shiny foliage, sticky items or decks underneath and around the affected plants. Aphids secrete a sticky honeydew substance, which attracts ants and bees. A sooty substance on the wood – aptly called sooty mold – notes chronic aphid infestation. This mold grows on the honeydew.

Control options are many. Soft insecticides, including soaps and oils, are often high on the list. While soft on the environment, these products may harm the treated plants. Soaps contain alcohol and can dehydrate the leaf surface and cause burning or leaf drop in sensitive plants. Horticultural oils are effective in smothering the insects – but again, read the label and check for plant sensitivity. For instance, oil will change the color of blue spruce to green.

Topical insecticide sprays will work for most infestations, except when the aphids cause the leaves to curl. If you have to uncurl the leaf to see the aphids, a topical insecticide spray is often ineffective, as the spray can’t get to the offending insects.

Systemic insecticides (those that translocate in plant tissues) offer the most complete and longest lasting control of aphids. Products containing the active ingredient imidacloprid are the most effective and offer excellent plant safety.

As the weather warms this summer, plants should get some respite from aphid infestations. However, aphid populations generally build beginning around Labor Day and continue into the fall.

The author is a certified arborist with Swingle Tree & Lawn Care, Denver, Colo., and can be reached at 303-337-6200.