Get ready for ash-lilac borer

Photo: Whitney Cranshaw, Colorado State University, www.forestryimages.org

Although the exotic emerald ash borer is capturing headlines, growers should also consider a more common foe: the ash/lilac borer, Podosesia syringae, a native insect that feeds on ash, lilac and privet.

Ward Upham, extension associate with Kansas State University, covers it in this week's horticulture newsletter:

If you have had problems with canes or stems of lilac and privet suddenly wilting, or ash trees that show borer holes in the trunk and larger branches, the ash/lilac borer may be to blame. This insect causes the base of infested lilac stems to swell and the bark to separate from the wood. A fine sawdust-like material is present around holes in the canes. Ash and mountain ash also are affected. The borer attacks the trunk, which may cause bark to swell and crack if there are repeated infestations.

Ash/lilac borers overwinter as larvae in infested trees and shrubs. Moths generally begin to emerge in mid to late April but will be late this year; probably by about 2 weeks. The moth has clear wings and resembles a wasp. There is one generation per year. Public and commercially managed properties often use pheromone traps to determine the presence of adults.

Spray treatments are started seven to 10 days after capture of the first moths. Sprays also can be timed using phenology, the practice of timing one event by another. Look for active ingredients of bifenthrin or permethrin in products labeled for control.

The first spray for ash/lilac borer should be applied when the Vanhoutte spirea is in full to late bloom, probably by about May 15 this year. 

Apply a second spray four weeks after the first. Thoroughly treat the trunk and larger limbs of ash or the lower portion of the stems of lilac or privet. Heavily infested ash should be cut and burned during the fall and winter. Infested stems of lilac or privet should be removed as well.

Click here to read the rest of the newsletter, or e-mail cdipman@ksu.edu to subscribe.