–by Raymond Cloyd
It is that time year to be aware of and prevent damage from the ash/lilac borer (Podosesia syringae). Ash/lilac borer adults are generally active from late-April through June, although the extended cool period we experienced in April more than likely shifted initial activity into early to mid-May. Adults are brown, clearwing moths that resemble paper wasps (Figure 1). Adult females lay tan, oval-shaped eggs in cracks and crevices, or wounds at the base of plant stems. A single female can live about one week and lay up to 400 eggs. Below are nine items related to the life history parameters and management strategies associated with the ash/lilac borer:
- 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.
- 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.
- Evidence of larval feeding includes the presence of light-colored sawdust (frass) that accumulates at the base of infected trees or shrubs (Figure 2).
Fig 2. Sawdust Located At The Base Of An Infected Tree (Author–Raymond Cloyd, KS)
- Ash/lilac borer overwinters as a late-instar larva located in feeding tunnels or galleries.
- Trees or shrubs that have been infested with ash/lilac borers will have brown papery pupal cases protruding from the bark (Figure 3). These are where the adults emerged from.
Fig 3. Pupal Cases Of AshLilac Borer Protruding From Tree Trunk (Author–Raymond Cloyd, KSU
- 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.
- Insecticides containing the active ingredients, permethrin 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.
- Pheromone traps are commercially available that capture adult males (Figure 4), 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.
Fig 4. Pheromone Trap Used To Capture AshLilac Borer Adult Males (Author–Raymond Cloyd, KSU)
For more information regarding ash/lilac borer management contact your county or state extension specialist.