Protect birch trees from deadly beetle
file photo
Jack Stivers MSU Lake County Extension Agent
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One of our more serious shade tree pests is the bronze birch borer. Birch trees that are under attack by these insects usually show symptoms first at the top of the tree. Symptoms are yellowing of leaves, then dieback that begins at branch tips and works down the tree. Ridges or ripples beneath the bark or wet spots or dark staining are clues that the dieback is being caused by the bronze birch borer and not by environmental conditions or plant diseases. The ridges are caused by tunneling and feeding activities of immature beetles, which are in the larval stage. If the tree was infested last year, you might find D-shaped holes about one-eighth-inch long in the bark where the adult beetles emerge.
The adult beetles are present in mid-to-late June and again in July. They lay eggs in the cracks and crevices of the tree bark, the eggs hatch into the larvae, which tunnel into the tree to the region just under the bark. The larvae will become adult beetles the following summer, when they chew their way out of the tree, leaving the D-shaped holes.
Unfortunately, by the time symptoms are visible it is often impossible to save the tree. So the key is to protect birch trees by keeping them strong and vigorous, preventing drought stress, over-fertilization or under-fertilization, or injury — all of which can cause problems. Tree borers seldom attack healthy, vigorous trees. If the water table is fairly deep or soils dry out quickly in your area, trees can be drought stressed quite easily, making them susceptible to pest problems. Nearly all the tree roots are in the upper 18 inches of soil so regular watering of birch trees may be needed. Water the entire area under the tree canopy and half again as far because the roots extend more than twice the distance of the branches. Allow water to soak to depths of about three feet. Frequency of watering will depend on location and natural precipitation. Soil tests can determine if fertilization is needed or not. In many parts of Lake County, trees do not require fertilizing. Unnecessary fertilizer applications can actually stress the trees, again making them susceptible to pest problems.
When planting new birches, select varieties that are least susceptible to attack by this insect and plant birches only if the growing conditions and soil type in your yard are suitable for those specific trees. Always buy any plant, including birches, to suit the spot rather than buying the plant, then looking for a place to put it.
Preventative treatments can be made using a few protective products that have a systemic effect in the tree and don’t allow birch borers to enter. These products can be applied by anyone and in some cases will protect the tree for the full season. Be sure to first apply before June so the trees are protected before the bronze birch borer emerges.
