Ash borers spread in Cook County -- chicagotribune.com: "Trees in south and southeast Cook County forest preserves have been found to be infested with emerald ash borers, which have already killed millions of trees throughout the upper Midwest."
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They are pretty little bugs, but the ash borer may turn out to be a horrifically expensive pest for municipalities and homeowner associations. The infested trees have to be cut down and removed, and that costs $500 per tree at least, according to one arborist I spoke with.