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Bur Oaks, Bugs and Birds (06/20/19)

In several communities around the state, young bur oak trees are showing damage from woodpecker activity.

In several communities around the state, young bur oak trees are showing damage from woodpecker activity. The damage is highly variable, but at its worst, some trees have been mostly girdled or had the main stem killed. The birds are not to blame, however, as they have been searching for a tasty meal – insect larvae located within the bark. We believe the insect is a stingless wasp with the scientific name Callirhytis flavipes; it does not yet have a common name.

The birds seem to be focusing on young trees, those with stem diameters (at 4.5’ above the ground) from 1” to about 8”. Larger trees may be affected as well, but the damage on those trees seems to be less severe. Some trees have escaped with no damage at all, especially those trees with smoother bark. Nearby trees may have destruction up-and-down the entire stem. Examples of this problem have been seen throughout the eastern part of the state, as well as in the Bismarck-Mandan area. We haven’t heard of any problems in conservation (shelterbelt) plantings, but it is definitely a possibility.

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In a heavily infested tree, the main leader can be killed, which then must be pruned out. The result is a tree with poor structure that is stressed and might not survive in the long term. Some trees have been attacked more than once and are damaged to the point that they must be removed. Unfortunately, the only recommendation we have at this point is to prune out dead branches. We’re continuing to monitor the situation and searching for solutions. While systemic insecticides might offer some level of control, no research on this topic has been published. A product called Tanglefoot Bird Repellent may deter birds from digging into the tree bark; however, since the birds don’t feed on the trees until winter, applying the product right now will not help.

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Joe Zeleznik

NDSU Extension Forestry Specialist

 

Lezlee Johnson

ND Forest Service

Forest Health Manager

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