Last year I received many calls on this phenomenon that seemed to plague many trees during the hot summer months. You may have noticed holes in some of your trees and shrubs at that time and wondered if it’s the works of a woodpecker or just the way that particular plant grows. These holes can become a pest that leads to dead limbs. This is not a coincidence: the more holes you find, the more damaged the tree becomes. These are the interesting works from the Ash/Lilac Borer. Now is the time to take action to prevent the borers from boring into your plants.

Here’s what you need to know about the Borer:

Typically, there is one generation of ash/lilac borer per year in Kansas. Adults are typically active from late-April through June, although activity thrives on temperature. Adults are brown, clearwing moths that look similar to paper wasps. Adult females lay tan, oval-shaped eggs in cracks and crevices or wounds at the base of plant stems. This is where proper treatment should be emphasized due to the nature of the borer larvae feeding at the base of plant stems. This causes swollen areas or cracks, and they also feed where major branches attach to the trunk. Take considerations because one female can live for approximately one week and lay up to 400 eggs. The larvae are responsible for causing plant damage by tunneling and feeding within the bark (cambium). Larvae can also tunnel further into the wood and feed within the sapwood and heartwood. Ash/lilac borers overwinter as a late-instar larva located in feeding tunnels. This larval stage is crucial for proper management because larval feeding restricts the flow of water and nutrients; thus, resulting in shoot or branch dieback (dead limbs).  

Here are some tips to identify and prevent damage from these critters:

1. If you notice the presence of light-colored sawdust (frass) accumulating at the base of infected trees or shrubs, this is evidence of larval feeding.

2. Trees or shrubs infested with ash/lilac borers will have brown papery pupal cases protruding from the bark (Figure 3), which is where adults emerge from.

3. Avoid “plant stress.” It is easier for borers to attack a plant when they are weak andmore susceptible. Try to keep your shrubs and trees healthy by providing proper cultural practices such as watering (irrigation), fertilization, pruning and mulching.

Mulch Tip: A two- to three-foot wide mulched area around the base of trees and shrubs prevents injury from lawn mowers and weed-trimmers that can girdle trees and shrubs leading to stress.

4. Adults are typically present in late spring through early summer (under normal weather conditions), so it is best to avoid pruning at this time, as the volatiles emitted from pruning cuts may attract adult females.

5. The chemical route: insecticides containing the active ingredients, permethrin, bifenthrin, or chlorantraniliprole (Hi-Yield Garden, Pet, and Livestock Insect Control and 38 Plus Turf, Termite & Ornamental Insect Control) can be applied to the bark— at least up to six feet from the base — to prevent borer larvae from entering plants after eggs hatch. After eggs hatch, ash/lilac borer larvae crawl on the bark searching for entry points, which exposes them to insecticide sprays. Once larvae are inside the plant, they are not susceptible to insecticide sprays. Systemic insecticides applied to the soil or injected into trees or shrubs do not provide reliable control of the ash/lilac borer.

6. Use pheromone traps to capture adult males and commercially available, which help estimate when females will be laying eggs. Pheromone traps help appropriately time insecticide applications. Insecticide spray applications should begin seven to 10 days after capturing the first adults. Check pheromone traps two to three times per week for the presence of newly captured adult males.

Elizabeth Espino is the Agriculture and Natural Resources Agent for Cowley County Extension. She can be reached at (620) 221-5450 or

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