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Avoid plant stress it manage ash/lilac borer
Alicia Boor
Alicia Boor

Now is the time of year to prevent or alleviate damage from the ash/lilac borer. Ash/lilac borer adults are usually active from late April through June, although activity is dependent on temperature. Adults are brown, clearwing moths that resemble paper wasps. Adult females lay tan, oval shaped eggs in cracks and crevices, or wounds at the base of plant stems. One female can live for approximately one week and lay up to 400 eggs.

Below are nine key points associated with the biology, ecology, and management of the ash/lilac borer:

1. Larvae cause plant damage by tunneling and feeding within the bark (cambium). Larvae will also tunnel further into the wood and feed within the sapwood and heartwood.

2. Feeding by the larvae restricts the flow of water and nutrients in plants, resulting in shoot or branch dieback. Ash/lilac borer larvae feed at the base of plant stems causing swollen areas or cracks, and they also feed where major branches attach to the trunk.

3. The presence of light-colored sawdust (frass) accumulating at the base of infected trees or shrubs is evidence of larval feeding.

4. Ash/lilac borer overwinters as a late instar larva located in feeding tunnels or galleries.

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

6. There is usually one generation per year in Kansas.

7. The primary means of managing ash/lilac borer is to avoid plant stress by providing proper cultural practices including; irrigation (watering), fertilization, pruning, and mulching. In general, plants that are stressed are more susceptible to attack by ash/lilac borer than plants that are healthy. A two to three-foot-wide mulched area around the base of plants prevents injury from lawn mowers and weed trimmers that can girdle plants leading to stress. In addition, avoid pruning plants in late spring through early summer because adults are usually present and the volatiles emitted from pruning cuts may attract adult females.

8. Insecticides containing the active ingredients, permethrin, bifenthrin, or chlorantraniliprole can be applied to the bark—at least up to six feet from the base—to prevent ash/lilac borer larvae from entering plants after emerging (eclosing) from eggs. After larvae emerge (eclose) from eggs, they move around on the bark searching for entry points, which exposes them to insecticide spray applications. Once larvae are inside the plant, they are not susceptible to insecticide spray applications. Systemic insecticides applied to the soil or injected into plants will not provide protection from ash/lilac borer larvae feeding.

9. Commercially available pheromone traps capture adult males, which helps in estimating when females will be laying eggs. Pheromone traps assist in timing insecticide applications when the larvae are present, which will result in killing larvae before they enter plants. 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.

Alicia Boor is the Agriculture and Natural Resources agent with K-State Research and Extension – Cottonwood District. Contact her by email ataboor@ksu.eduor call 620-793-1910.