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Denver Tree Service: Learn the Differences Between Lilac Ash Borer and Emerald Ash Borer


April 21, 2016

The dreaded scourge of ash trees everywhere--the emerald ash borer--has spread to Colorado. Ash trees in Colorado already suffer from a native pest, the lilac ash borer. Both species cause destruction, but they’re not the same. With assistance from the Colorado State University Extension, Denver tree service companies explain the difference.
The lilac ash borer is native to North America and prefers already-stressed trees, white ash being favored over green ash. This pest is the larva form (caterpillar) of a moth which is a type of clearwing borer. An early-season pest, the lilac ash borer concentrates egg laying in the bark on the lower trunks of trees.

The emerald ash borer is an Asian invader. Despite bans on transportation of firewood and infested wood, the emerald ash borer has spread steadily across North America. Thus far, only the most western states remain unaffected. This aggressive borer is the larva of a type of beetle known as the “metallic wood borer” and favors green ash over white ash. The emerald ash borer lays eggs on the bark surface throughout the tree from late May through early July.
If the unstoppable invasion of the emerald ash borer weren’t distressing enough, research at Wright State University discovered that the emerald ash borer has expanded its diet. Apparently, the pest finds the white fringetree, a relative of ash, tasty and hospitable.

The white fringetree is native to the savannas and lowlands of the southeastern United States. It is a small, deciduous tree with fluffy, white flowers. It is also known as Graybeard or old man’s beard and most often used as an ornamental in landscaping. It resembles the Chinese fringetree, an import native to eastern Asia with dense clusters of small, white flowers.

Pest Damage

After hatching, lilac ash borer larvae tunnel through the bark and feed in the interior of the tree. Heavily infested trees will show deformities in affected trunks and branches. Emerald ash borer larva also tunnel through the bark to feed on the tree’s interior just under the bark. Their feeding paths girdle the tree which show outwardly as a progressive thinning of the tree canopy.

Pest Management

Treatment of lilac ash borer infestation involves the use of a spray insecticide applied to the trunk and lower branches of the affected tree. Tree pros time the application to either immediately before or at the same time the eggs begin to hatch.

Treatment of emerald ash borer infestation involves repeated applications of insecticides via sprays, trunk injections, and soil treatments.


Treatments used to control lilac ash borer infestations are not appropriate for emerald ash borer infestations.

Your Best Resource

American Arbor Care offers numerous insect treatments throughout the growing season to keep your trees and shrubs healthy. Trust the tree service service professionals to accurately determine the pest infestation and to know how to control it. Call us at (303) 639-8584 to schedule a consultation and learn what can be done to make your lawn the envy of the neighborhood.
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