Bronze Birch Borer

By The Old House Web

Bronze Birch Borer

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The damage caused by bronze birch borer is very visible but the insect is rarely seen.

The insects overwinters as larvae in the trunks of birches. In the spring the larvae mature and pupate in the tree trunk. The adults emerge from the tree at the end of May or in early June. The adult females begin to lay eggs on the tree trunks preferably near a wound or injury. The larva hatches out of the egg and bores into the tree trunk. The larvae can be in the tree one or two years.

The main symptom is death of the upper branches of the tree. All the leaves on affected branches turn brown the the leaves are entirely brown. The injury should not be confused with the partial browning of leaves caused by birch leaf miner. Close inspection of the trunk will often reveal the adult emergence holes. These can be either round or semi-circular.

Control involves keeping trees healthy and pesticide applications. Keeping trees healthy with regular fertilizer and watering during dry weather will reduce tree susceptibility. Such measure do not prevent infestation. Birch trees should not be planted on dry, adverse sites as they will be more borer susceptible. Applications of the insecticide Dursban are timed to kill the larvae as they hatch out in late May to early June.

At least three birch trees have been reported as being resistant to bronze birch borer. The are monarch birch, Betula maximowieziana, the Japanese birch, Betula platyphylla and the river birch, Betula nigra. The river birch does not have the smooth white bark that makes birch a desirable ornamental tree. Resistance can only be assured after the trees have have been used in landscapes and are found to have little problem with borer.

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