Ash Borers: Destructive, but can be easily controlled

Gretchen Mayer
Special to the American News

Shelterbelts might be looking a little rough right now, but there is good news and bad news on that front.

While many trees are being attacked by ash borers, they are not the invasive Emerald Ash Borer (EAB) that is hitting the Sioux Falls area.

"What we're seeing is a native ash borer that we've always had," said Aaron Kiesz, Aberdeen City Forester. "They're not new, it's just that people are more aware of the problem."

They tend to hit trees that are in poor condition and the weather has a definite impact on the health of a tree. An unhealthy tree is more susceptible to infestation.

"We had an excessive drought followed by excessive moisture and that stresses the trees out," Kiesz said. "And in many shelterbelts the trees are fairly close together."

There are two types of borers that are common to this area: the banded and the clear wing, which can also affect the common lilac bush. Because the banded borer is less prevalent and only attacks mostly dead trees, it's an infestation of clear wing borers that will need intervention.

"Almost any ash tree will have some borers," Kiesz said. "What you need to look for is more extensive pockets of infestation. Just because you find a couple of holes doesn't necessarily mean that you need to spray."

According to Kiesz, one indication is a decline in the top portion of the tree.

"This can be tricky because the ash trees in our part of the state tend to look a little rough anyway," he said. "Also look for multiple exit holes. Generally they are about the size of the end of a pencil."

Another way to tell if you have an ash borer problem is to keep an eye out for their natural predator.

"If you have a lot of woodpecker activity, you might have a problem," he said.

For homeowners, encourage woodpeckers to hang out in your yard by hanging suet blocks.

Now for the good news.

"The shelterbelts are looking rough right now because of the drought last year so we should see a good turnaround in the shelterbelts next year. Trees always take a year to rebound," Kiesz said. "And when the belts were put in, a lot of times the trees and shrubs were planted too close together. There are a couple of reasons for that.

"First of all, farms want a good solid row of trees to block the wind. But also, they overplanted, expecting some of the trees and bushes to not survive. You can prevent infestation by trimming out the unhealthy trees and opening up the belt to more air and sunlight. It helps the existing trees that are doing well by taking out the marginal trees."

While prevention is the best bet, if that is not possible, spraying is an option.

"It's more difficult for farmers because they're dealing with so many trees. However, there are simple sprays available. For the clear-wing ash borer you spray the trunk down one time in May. This will kill the adult insects and also the larvae before it bores into the tree.

"If you hit it right you might get good control. If not, you may need to spray every other year. You can always tell if the holes are fresh because the borers kick out sawdust when they exit."

When spraying, make sure that the active ingredient is Permethrin and that it is labelled for the ash borer. Closely follow the mixing instructions. While it's fairly safe for humans and has been used to treat head lice and scabies, it is toxic to cats and fish.

Kiesz advises that those planting a new shelterbelt should "definitely avoid ash trees. They should be planting a diverse belt which includes diversity within the rows themselves. Hackberry, Bur Oak, Honeylocust, Aspen, Kentucky coffeetree, native cottonwood, and Linden are all good shade trees."

Imagine what it would be like to have no ash trees in South Dakota. It's happened in thirty-one other states and Canada. The Emerald Ash Borer is a nasty, determined insect about a half-inch long. While there are no signs of it in the northeast corner of South Dakota, Sioux Falls has been affected.

Check out the management plan on Aberdeen's website https://www.aberdeen.sd.us/147/Forestry-Division.

An ash tree with an infestation of clear wing ash borers. These are the holes they make when they exit the tree. The hole will be about the size of a pencil eraser. If sawdust is present, that is the sign of a fresh hole.
The clear wing ash borer. Can be controlled by spraying trees with Permethrin mid-May.
Aaron Kiesz, Aberdeen City Forester