Common Questions on the Emerald Ash Borer

Dr. John Ball, extension forestry specialist, South Dakota State University, forest health specialist, SD Division of Resource Conservation and Forestry; phone 605.688.4737. email john.ball@sdstate.edu

What is the emerald ash borer?

The emerald ash borer is a small beetle that was accidentally introduced from China into the Detroit area of Michigan sometime during the 1990s. The larval (worm) stage of the insect feeds in the food-conducting tissue of the tree’s trunk severing the flow of food from the leaves to the roots.

Why is there a concern?

The emerald ash borer was first detected in the southeastern Michigan in 2002. Since that time it has spread out into the surrounding states and Canadian providences. There have been more than 40 million ash trees killed since the beetle was discovered in this country. The closest infestation to South Dakota was found in May 2009 in St. Paul, Minnesota. This infestation is now estimated to be three to five years old. Since no one ever finds the first infested tree in an area there is a strong possibility that there are more infestations further west. The emerald ash borer will probably be detected in South Dakota sometime in the next several years.

Will the emerald ash borer survive in South Dakota?

Yes, it is from northeastern Asia and is adapted to our cold winters and hot summer.

Will we loss all of our ash to this insect?

Based on the experience in other states, the answer is yes. However, it will take many years to spread across the entire state. Typically when the beetle is found in a community the infestation spreads very fast through the town and the trees are killed within a few years but the spread between communities or counties can be very slow if the movement of infested wood is stopped. There still are counties in Michigan and Ohio that are not yet infested though the insect has been in these states for more than a decade. We will probably see the same pattern here, and in fact, due to the isolation of our small communities the movement may be very slow.

What trees are attacked by the emerald ash borer?

All species of ash are attacked by this insect. Our black, blue, green and white ash trees and their many cultivars are all susceptible to attack. All of these trees will be killed by an emerald ash borer infestation. The only tree showing some tolerance to attack is the Manchurian ash, a tree native to the region of Asia where the beetle is found. Emerald ash borer does not attack mountainash, ash-leaf maple or prickly ash. These trees are not related to ash.

How can I tell if my tree is infested?

Again, it is important to point out that the emerald ash borer has not yet been detected in South Dakota (January 2012). However ash trees exhibiting the following symptoms may be infested. Look for ash trees that have some dieback or are standing dead. Oftentimes these trees will have the bark shredding off due to the tremendous number of woodpeckers feeding on the larvae beneath the bark of the infested tree. If the bark is pulled off the tree you should be able to find S-shaped tunnels on the surface of the wood. These narrow tunnels, about 1/8-inch wide, will be packed

It is important to remember that there are also many native borers that attack ash trees, the most common being the native ash borer. This insect can be separated from the emerald ash borer by its larger tunnels that are clear of sawdust. The exit hole made by these insects is round and almost the diameter of a pencil. There will often be sawdust around the base of trees infested by the native ash borer.

What else should I be doing?

Since the emerald ash borer has not yet been found in the state there is no need to begin removing ash trees. However, it is probably a good idea to stop planting ash. Ash trees make up almost 1/3 of all the trees planted in our communities and also are one of our most common windbreak species. There are many other trees that can be used as ornamental or windbreak trees and we should start planting trees now so when the emerald ash borer arrives we will not loss the majority of our community forests and windbreaks in a short time period. We also do not want to repeat the mistake made with Dutch elm disease where the diseased elms were replaced with a single species - ash. The best recommendation for homeowners is to look at what their neighbor’s are planting and plant something else! We want to develop a diverse forest, one that is not all susceptible to a single pest.

It is also too early to begin pesticide treatments. While there are effective treatments for the emerald ash borer they should be consider means of prolonging the tree rather than saving the tree. Experience in other states has shown that the beetle population can continue to increase in a treated tree if there is a high population of beetles in the area and these trees may die despite the use of insecticides. When the beetle is found in a region of the state, homeowners may want to consider treatments but the most effective are the ones available to commercial applicators and it may be best to leave the management on the problem in the hands of professional tree care companies.