Bronze Birch Borer
The wood boring beetle, bronze birch borer is a very serious pest of the white birch tree in the Midwest. It can severely injure and kill all varieties of white birch. The bronze birch borer only attacks trees in a weakened condition. Most often, the trees become weak because of drought, nutrient deficiency, construction injury, or excessive heat. Planting birch trees in unsuitable locations is the main reason for problems with bronze birch borer.
Life Cycle
This insect overwinters as a larva in the tree. Adults begin emerging from the tree in late May to early June depending on the weather. Adult emergence can last up to six weeks. The emergence holes are D-shaped. The adults lay eggs singly or in clutches under the bark flaps or in bark cracks in the branches or trunks. When the eggs hatch, the larvae bore directly into the wood to begin feeding and to mature into adults. The insect can mature in one year's time; however, most take two years to reach adulthood.
Symptoms and Effects
The first sign of attack is usually a thinning or dieback of branches in the upper third of the tree's canopy. Leaves on infested branches may be stunted, yellow or show marginal browning in May or June. Larvae cause the damage by feeding under the bark and girdling the branches, which prevents water and nutrients from reaching the branch about the attach site. Over time, damage progresses downward to lower branches and the trunk. Typically, borers kill trees in three to four years. Very weak trees may die in one year.
Prevention and Control
The best control is prevention. Birch trees should not be planted in hot, sunny locations or on hills. Planting in semi-shade is best. Also, choose native varieties of trees. They are less susceptible to borer attacks. It is essential to keep existing trees healthy. Because birches have a shallow root system, water them during periods of drought. Keep the soil around them cool by placing a ring of organic mulch around the tree. Fertilizing in the fall or spring can help the trees remain vigorous.
Treatment
As a rule, if more than a third of the tree is infested, saving the trees becomes less likely. If less than one-third of the canopy is infested, saving the tree is possible, but not always successful. The first thing to remember is that the insect only attacks weakened trees. The larvae do not generally attack healthy trees.
The most important first step in treating an infested tree is to improve the growing conditions through proper watering, mulching, and fertilization.
The second step is to remove the borer infected branches and any deadwood from the tree. Pruning should be done August through April so that the adults will not be attracted to the wounds of the tree. To prevent the breeding and spread of adult bronze birch borers, remove or destroy dead and dying trees. Use all birch firewood before spring.
Finally, the insect needs to be chemically controlled with an insecticide.
Please contact your RYANPro for more information about recommended treatment.