Landscape - Borers in Trees

The following is a short article on borer pests that can attack trees in Delaware that will be active soon.

Three serious pests of landscape trees - dogwood borer, bronze birch borer, and flatheaded appletree borer - soon will be emerging. The dogwood borer is the most serious pest of ornamental dogwoods, especially stressed trees in full sun. The bronze birch borer is a severe pest of white or paper birch, especially cultivated trees under stress. Flatheaded appletree borers are major pests of red maples, hawthorns, flowering crabapple, and several other hardwoods, especially those which are newly transplanted or under stress. Mated females of all three species fly to host trees and lay eggs on the bark.

Management -- Borers rarely injure healthy trees or shrubs growing in their natural environments. When transplanted into landscape settings, every effort should be made to minimize plant stresses such as drought, soil compaction, sun scald, lawn mower/weed trimmer injuries, etc. Because newly planted trees are under considerable stress, preventive sprays are advisable during the first 2-3 growing seasons after planting. Timing is crucial in order to have a lethal residue of insecticide on the bark to intercept newly-hatched larvae before they burrow into the tree. Mid-May to late May is about the time to apply protectant sprays for all three species. Dursban (chlorpyrifos) and Lindane are no longer available, but professionals can use Onyx (bifenthrin) or Astro (permethrin).

Adapted for Delaware from "BORER ALERT" By Mike Potter in the May 5, 2008 edition of the Kentucky Pest News from the University of Kentucky College of Agriculture.