As you may have noticed in our area, birch trees seem to have a hard time surviving. People tend to blame this on the Bronze Birch Borer, but many times the borers are not the real culprits.

Birch trees grow best in shady areas with a good moisture supply and a sandy soil moisture. This is just the opposite of the conditions we provide them. We plant them in heavy clay soil and full sunlight. Our dry conditions and the high nitrogen fertilizers we use on our lawns are also hard on the birches. They frequently will survive only 15-20 years in the Red River Valley.

A birch tree or clump struggling along in such an unfavorable site will lose vigor and become weakened, thus opening the door for infection by the Bronze Birch Borer. Another interesting fact: Adult borers prefer to lay eggs on trees in full sunlight.

The adult borer is a greenish bronze colored beetle, which emerges from holes in the branches and trunk of the birch normally in early to mid June. They will continue to emerge over a three week period. The adults feed on birch foliage and about a week after emergence begin laying eggs in the cracks and crevices in the bark. The eggs hatch into tiny white larvae which tunnel under the bark. They produce galleries which are packed with a dark brown sawdust like frass. The tunnels often girdle the branches, cutting off the sap flow and killing the area above the girdle. If the top of your birch has died, check under the bark of the dead branches for borer galleries. They are very easy to find. The best time to initiate control is when the adults are feeding on the foliage. The chemical insecticide Lindane can be used for control. Spray 3 times at 3 week intervals starting in mid-June.

Remember that you can suppress birch borer attacks by frequent watering (especially during dry periods), proper fertilization and pruning of dead or dying branches.

This page was last updated April 2003

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