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Birch Tree Problems

There are two common insect problems found on birch trees. The bronze birch borer and the birch leaf miner.

Thinning or dying birch tree crowns, which are the upper branches, probably mean the trees are infested with bronze birch borer. You can save infested trees by detecting the problem early.

European birch tends to be more susceptible to borers than the native paper birch. River birch is mostly borer free. Borers are most likely to attack trees that have been weakened from a hot and dry location or by a lack of fertilizer. Vigorous, healthy trees are less attractive to borers and are better able to survive a borer attack.

The site where you grow birches affects their borer resistance. Birch do best on a north facing slope or where plants or man-made structures keep soil cool, shaded and moist. The trees weaken in areas where they must endure soil compaction from foot traffic or a lack of moisture and high temperature conditions.

To help prevent borer problems, fertilize the trees so they grow vigorously. Be sure to water during prolonged dry spells.

If you see small, yellowish spots that enlarge and turn brown developing on the leaves of your birch trees, they are probably infested with birch leaf miner. Treat the tree in spring to prevent unsightly miner damage.

The birch leaf miner is a tiny insect that attacks all kinds of birch grown in North Dakota, including European, paper and river birch. Adult miners emerge in early May and lay their eggs in the new expanding leaves. Although several crops of adults emerge over the summer, it is this first group that does the most damage. Later attacks are usually confined to the youngest leaves at the branch tips.

The first symptoms of leaf miners are the small, yellow, translucent spots on the leaves. After 1 to 2 weeks, the spots enlarge as the leaf miners tunnel between upper and lower leaf surfaces. The leaves become brown and papery and eventually drop off.

Foliar sprays will control leaf miners and borers if you apply them when the first symptoms of leaf miners appear, or if the birch has had previous, minor damage from borer activity. Use products containing Lindane or Orthene in their emulsifiable concentrate forms, according to label directions.

If you have more questions, contact your county office of the NDSU Extension Service for additional information on birch trees.

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