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Two-lined chestnut borer and bronze birch borer

The on-going saga of drought, mature trees, and flathead borers continues in Region I, especially in the northern part of the region. For example, the bur oak in an area of housing development and wooded lots on the shore of Lake of the Woods a few miles north of Baudette have been hard hit by two-lined chestnut borer, Agrilus bilineatus, along with associated Armillaria root rot. More than fifty percent of the oaks have thirty percent or more crown die-back with numerous dead trees around the housing development. Pin oaks that were planted around the campground by the golf course nearby are also affected. Although bur oak can withstand drought very well, they are particularly sensitive to changes in their environment such as fluctuating water tables. Mortality and crown die-back were also reported around Kelliher in Beltrami County in 1997.

Bronze birch borer, Agrilus anxius, continues to cause extensive mortality of paper birch in Region I, especially over the past two years. Birch mortality from BBB increased sharply during the early 1980's, somewhat leveled out in the late 1980's only to become more active in the past few years.

Recommendation. If oak or birch trees have fifty percent or more crown die-back in early summer, they should be removed by July 15th of that current year. The wood should either be destroyed, debarked or used as firewood. To store as firewood, the wood should be covered with a plastic tarp and dirt piled around the bottom edge of the tarp. Leave the tarp on for one whole year then the wood can be used. If the trees remain stressed and dying branches and trees are not removed, the insects propagate and more trees will be infested the following summer. Armillaria root disease from cut stumps can invade root systems of nearby stressed trees.