1. The larvae cause plant damage by creating tunnels and feeding within the bark (cambium). In addition, larvae can tunnel further into the wood and feed within the sapwood and heartwood.
2. Larval feeding restricts the flow of water and nutrients resulting in shoot or branch dieback. Ash/lilac borer feeds primarily at the base of plant stems creating swollen areas or cracks, and where major branches attach to the trunk.
3. Evidence of larval feeding includes the presence of light-colored sawdust (frass) that accumulates at the base of infected trees or shrubs.
4. Ash/lilac borer overwinters as a late-instar larva located in feeding tunnels or galleries.
5. Trees or shrubs that have been infested with ash/lilac borers will have brown papery pupal cases protruding from the bark. These are where the adults emerged from.
6. In Kansas, there is generally one generation per year.
7. The best way to minimize problems with ash/lilac borer is to avoid ‘plant stress’ by providing proper cultural practices, such as; irrigation (watering), fertilization, pruning, and mulching. Stressed plants, in general, are more susceptible to attack than so called ‘healthy plants.’ A two to three foot wide mulched area around the base of trees and shrubs prevents injury from lawn mowers and weed-trimmers, which can girdle trees and shrubs thus leading to ‘stress.’ Furthermore, avoid pruning plants in late spring through early summer (under usual weather conditions) as this is when adults are typically present and the volatiles emitted from pruning cuts may attract adult females.
8. Insecticides containing the active ingredients, permethrin (Hi-Yield Garden, Pet,
and Livestock Insect Control and 38 Plus Turf, Termite & Ornamental Insect Control) or bifenthrin can be applied to the bark, at least up to six feet from the base, in order to prevent ash/lilac borer larvae from entering plants after eggs hatch. Ash/lilac borer larvae crawl on the bark searching for entry points, which exposes them to insecticide residues.
9. Pheromone traps are commercially available that capture adult males, which helps to estimate when females will be laying eggs. Pheromone traps help in timing insecticide applications. Insecticide spray applications should begin 7 to 10 days after capturing the first adults. Be sure to also check pheromone traps two to three times per week and record the number of newly captured adult males. (Raymond Cloyd)
Editor’s Note: If you unable to use traps, apply the first spray when the Vanhoutte spirea is in full to late bloom and a second spray four weeks later. Vanhoutte spirea is the white-flowered spirea with arching branches that is in bloom now in the Manhattan area.