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Beware the Emerald Ash Borer

Peyton Garcia
Peyton Garcia
Posted on August 29
Left: An adult emerald ash borer. Right: Tell-tale tunnels left by borer larvae under the tree bark.

Left: An adult emerald ash borer. (Monique van Someren / Getty Images) Right: Tell-tale tunnels left by borer larvae under the tree bark. (corfoto / Getty Images)

In June, officials confirmed the first appearance of emerald ash borers on Colorado’s Western Slope. This invasive wood-boring beetle native to East Asia feeds under the bark of ash trees, cutting off the flow of water and nutrients, causing a slow and gradual death for the tree. The beetle was first found in Colorado 10 years ago in Boulder; entomologists called the pest “the most destructive and economically costly forest insect to ever invade North America.”

Colorado State University reports that roughly 15% of the state’s trees are ash, with nearly 1.5 million providing shade to metro Denverites. Over the last decade, the beetle has largely taken root in ash trees across north Denver, from Fort Collins to Longmont and Thornton to Arvada. Most recently, an infestation was confirmed in Littleton.

How to Spot an Emerald Ash Borer

If your ash tree is infested with these pesky little beetles it may exhibit some of these symptoms:

  • Sparse leaves or branches in the upper part of the tree
  • Vertical splits in bark possibly showing S-shaped “tunnels” underneath
  • Increased woodpecker activity
  • Miniature leaves at the tips of branches late in the summer

Prevention, Mitigation, and Eradication Measures

  • A tree can be infested long before it begins to show signs of a health decline — treat your tree before you even suspect an infestation
  • Preventative insecticides should be applied every 2-3 years for the life of the ash tree
  • For a more holistic approach, some municipalities have strategically deployed tiny, stingless wasps to attack the beetles’ larvae. Woodpeckers also feast on borer larvae.
  • Never transport raw ash wood (often firewood) — the most effective way emerald ash borers spread is by hitching a ride on wood transported by humans
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