Lilac Ash Borer Southern Idaho

Introduction – What is a Lilac Ash Borer?

Lilac or Ash Borer (Podosesia syringae) is a moth species whose larvae feed on the living vascular tissue of ash (Fraxinus spp.) and lilac predominantly. 

Unlike the highly destructive invasive beetle – the emerald ash borer, the lilac/ash borer is a species native to North America and widespread in the U.S.

Lilac/ash borer can cause major damage on ash, lilac, privet and other plants in the olive family, with white ash being the most common target.

How to Recognize a Lilac Ash Borer Moth?

Lilac/ash borer adults are one inch long and have a wingspan about one and a half inches. The color ranges from black-and-yellow to orange-and-brown. The wings are clear and reduced when compared with other moths. The legs are atypically long. 

The look of the lilac/ash borer completely mimics that of paper wasps. That’s why many people will mistake a lilac/ash borer for a wasp, when in fact it’s a moth.

How to Recognize a Lilac Ash Borer Caterpillar?

A mature larva is about one inch long, white with a dark, rounded head typical of moth caterpillars. “Fake” legs – prolegs – that are present on its rear part are another clue that it is a moth and not a beetle larva.

Lilac Ash Borer Caterpillar Southern Idaho

Lilac Ash Borer Life Cycle

Adults will start to emerge in the spring, on mornings when the temperature is above 60°F. The exact beginning of the lilac/ash borer season depends on location, in Twin Falls Idaho and surrounding areas that’s usually late March or Late April.   

The female ash borer, who has a lifespan of only one week, lays her eggs on the bark of a tree, usually near wounds and other irregular surfaces.

Eggs are only 1/16 inch long and are oval and flattened, which makes them less evident on the bark. The female can lay them both in clusters and separately. 

Upon hatching, the tiny larvae will chew and burrow into the bark. Then they will start tunneling and feeding on the sapwood, and continue to do so during the summer. The larvae will pupate when the weather gets colder and the pupal stage will last through the winter. In the spring the cycle begins again.

What Damage Can The Lilac Ash Borer Cause?

Trees that become substantially damaged by lilac ash borer often develop a disfigured trunk, with irregular growth and excessive branching. Burrowing and tunneling within the tree and its structure may cause it to break under the influence of severe weather. 

Death of a tree caused solely by lilac/ash borer is a rare occurrence. However, most of the trees that break because of the infestation are removed for safety or aesthetical concerns. Also, secondary diseases can use entries and tunnels for their own proliferation. Pathological fungi that find their way to the inside of the trunk via borer tunnels are especially problematic.

Can Infested Ash Trees Be Saved from the Ash Borer?

The possibility of saving an infested tree largely depends on the extent of the damage. Trees in public spaces are especially problematic since we cannot be sure if the infestation has caused structural instability that will lead to a possibly dangerous break in the future. If possible, have a tree surgeon assess the situation. 

A young and vital tree may manage to overcome a mild attack of the ash borer, perhaps with suffering some minor deformities on the trunk. However, the survivor tree will still be weakened by the infestation and is at risk of hosting a new one in the next season. It might be a good idea to use chemicals to protect it, and continue to renew the protection yearly until the trunk’s diameter surpasses 6 inches. 

Physically supporting a young tree after the ash borer infestation is useful in preventing breaking when exposed to harsh winds.

Recommended Treatment

We recommend Bayer Advanced Tree and Shrub Protect and Feed its a high-quality product in this category, offering both 12-month protection and resilience-boosting nutrition for trees and shrubs, including the ash species.