Last month, officials confirmed some long-anticipated bad news: The invasive emerald ash borer has finally arrived in Denver. Since its initial appearance in the U.S. in 2002, the pest has decimated hundreds of millions of ash trees across the country.
This pesky wood-boring beetle is native to East Asia, and the havoc it wreaks on ash trees (which account for 1 in 6 trees in Denver) is irreversible. The beetle feeds under the bark of ash trees, cutting off the flow of water and nutrients, causing a slow and gradual death for the tree. It 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.
Have an ash tree? Here’s what you need to know:
How to Spot Emerald Ash Borer Activity
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 — so it’s best to treat it before you even suspect an infestation.
- You can also opt to replace your ash tree with something different. Apply for a free replacement tree through the city.
- 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.
