There has been a lot of talk about insects that could damage our ash trees and with so many ash trees planted in our landscapes we are always on the lookout. In order to help people to protect their ash trees we have placed pheromone traps in Yankton and have been monitoring the traps for adult clearwinged moths as they begin to fly. When I recently checked my ash borer trap it went from  having only a few adult male moths to over 35 male moths. This means that it is time to spray for the clear-winged ash borer.

Clearwinged borers belong to the order Lepidoptera, and the larval stages are typical caterpillars, whose eggs are laid by adult moths. Clearwinged moths are daytime fliers and otherwise appear very similar to wasps in coloration, having four somewhat tapered wings held wasp-like over the body when at rest. And their flight behavior is very wasp-like. However, their forewings are covered with overlapping scales, while the hind-wings are clear and transparent.

The larvae of clear-winged moths are typical caterpillars---white, with 6 short, segmented legs just behind the head, with 4 pairs of fleshy prolegs on the abdomen. Size may range from 1/8 to about 1 inch, depending on degree of maturity. Once larvae penetrate beneath bark and enter the wood, they begin to expand galleries, pushing coarse wood fragments and frass to the outside. The pupa of several species may push itself through, and be partially exposed in the exit hole just prior to emergence.

Lilac and Ash (Privet) Borers:

After mating, the adult females deposit eggs on the lower portions of the trunks or branches of ash, lilac or privet. The caterpillars bore into and feed within the stems or trunk and winter as partly grown larvae. Coarse chewings, often referred to as "frass" or excrement, are produced by boring caterpillars, and this material is pushed out from the burrows. Infested canes of lilac or privet may be heavily scarred and swollen near their bases, and may eventually die. Severely infested stems should be cut at ground level and destroyed each spring. The borer spends the winter in the pupa stage and there is only one generation each year.

It is important to regularly check young trees and shrubs that are becoming established in the landscape. Also, inspect the bases of trees for signs of egg clusters in bark crevices or wounds, or for emergence holes from which adults recently emerged. Sometimes you can actually find the pupal case of the emerging adult left in the exit hole.

Several cultural practices can reduce borer infestations. Trees that are strong and maintained in vigorous growing condition are not as attractive to borers. Trees should be properly watered, fertilized, and protected from pests, particularly during the first two or three years of growth and during drought periods that cause extreme stress.

Trimming damaged trees and eliminating weak ones is are very important management tools. Infested limbs, branches and trunks should be trimmed in the fall, burned or chipped and composted during the winter to reduce emerging borer populations.

Borer damage must be prevented because once borers gain access to cambium, sapwood, and heartwood, little can be done to control them

Chemical treatments are effective only if applied as residual sprays prior to egg-laying activity by the moths. If residuals are in place, young larvae are killed while attempting to invade the wood. According to Dr. John Ball, State Forest Specialist, ash borer treatments should be applied now. Treatment is done by applying a permethrin product like Astro (for commercial applicators) or Hi-Yield Garden, Pet and Livestock Insect Control for homeowners.

Remember to follow label instructions carefully so that good control is achieved, and that humans, animals and the environment are protected.

If you remove trees that are severely infested and you want to plant another tree look for varieties that are less prone to borer attack, such as oaks, lindens, crab apples, and conifers. Choose trees and shrubs that are suitable for the climatic zone in which they are planted. Those more vulnerable to the extremes of winter and summer in South Dakota will ultimately suffer damage and be attractive to borers.

For more information please contact your local Extension Office.

 Photograph courtesy of the University of  Nebraska.