Right now is the time to apply preventive borer sprays if you have an infested white birch tree that you are trying to protect from demise by the bronze birch borer. Dursban and lindane insecticides are available as trunk sprays to prevent the entry of new borers (beetle larvae) into the tree. Three sprays at two week intervals are required to get us through the adult emergence and egg laying period. Read and carefully follow label directions, especially personal protection precautions listed on lindane labels.
As has been frequently mentioned at other times, avoiding bronze birch borer (and other tree borers) is better than trying to control them. With bronze birch borer, avoidance is as easy as not planting susceptible white birch trees in sites for which the species is not suited. Birches are shallow rooted trees with little ability to withstand warm, dry and/or compacted soils. White birches planted in landscapes usually have ~two strikes~ against them from the start because of poor growing conditions. Presence of grass up to the tree trunks further stresses the landscape trees as they compete with the grass roots for water and nutrients. If you must have a white birch, and refuse to plant the hardier, native river birch, then pick your plating site very carefully for a cool, moist, well drained soil. Use a wood chip mulch over as much of the root zone as possible (to eliminate competition and to reduce moisture and heat stress), and plant away from paved areas where salt will be applied during winter.
Tolerant species of white birch as well as the preferred river birch are available from nurseries. Heritage river birch has light colored bark that may be acceptible as a substitute. Whitespire is a Japanese white-barked birch that is only attacked when under severe stress; bronze birch borer infestation is limited under good growing conditions.
This article originally appeared in the June 5, 1991 issue, p. 97.
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