Emerald ash borer’s eventual arrival threatens ash trees

By Elisa Sand
[email protected]

With 37 percent of trees lining Aberdeen’s boulevards being ash, the city forester is already concerned about a beetle that could badly damage the tree population when it arrives.

The emerald ash borer beetle is from Asia. It’s dark green in color and about a half-inch long. While the adults simply feed on the tree canopy, larvae burrow under the bark and into the tree and create S-shaped tunnels. The tunnels disrupt the tree’s ability to move water through the trunk.

When adult borers tunnel through the bark, they leave a D-shaped hole.

City Forester Aaron Kiesz knows it’s only a matter of time before the beetle is found locally, so the city is developing an emerald ash borer management plan that outlines the strategic removal of ash trees in rights of way like boulevards. It starts with taking down trees in marginal condition. They will be replaced with different species. Tree removal and planting in rights of way is at the city’s expense.

Introducing new trees gives them a chance to get established before emerald ash borer is found.

Aberdeen has about 12,842 trees in public rights of way — strips of grass between sidewalks and the city streets. Kiesz said that number is according to a survey of trees along about 99 percent of streets in town. It doesn’t include trees on private property. Kiesz estimates there are another 24,000 to 25,000 trees on private property.

Of the trees in rights of way, Kiesz said, roughly 4,800 are green ash. He said there are probably another 12,000 on private property.

Looming threat

Mike Jaspers, secretary for the South Dakota Department of Agriculture, spoke about the emerald ash borer at the recent Precision Ag Conference in Aberdeen.

“It’s not a matter of if we’re going to have to deal with this in South Dakota, it’s a matter of when,” he said.

The emerald ash borer has been found as close as 80 miles from South Dakota, Jaspers said.

With 40 percent of windbreaks in the state comprised of ash trees, he said, now is the time to start thinning them out and replacing them.

State Forester Greg Josten said a great replacement tree in a windbreak or shelterbelt is the Siberian larch, an evergreen that sheds its needles in the fall.

On average, about 30 percent of the trees in any South Dakota community are ash, Josten said, so some diversification is needed.

Kiesz agrees.

“Ideally, we don’t want more than 5 to 10 percent of one species in a boulevard,” he said.

Know your trees

Property owners should know what types of trees they have in their yards and on their land.

“We get calls from people who think they have an emerald ash borer, and they don’t have an ash tree,” Josten said.

Kiesz said he’s received the same calls, too. That’s because there are insects that attack other trees and also leave D-shaped holes. He said if residents are concerned about the trees on their property, he can take a look at them, but the city Forestry Department can only offer advice. If a tree on private property needs to be removed, the landowner absorbs the cost.

Removal costs can vary depending on the size and accessibility of a tree, Kiesz said. He estimated a range of between $500 and a couple thousand dollars.

If the tree’s condition is declining, Josten said, a property owner should consider replacing it with something different.

Green ash was a popular replacement after Dutch elm disease claimed many of the local elm trees, Kiesz said.

“Since 2005, we’ve lost 8,000 elms,” he said, estimating that loss at about 12,000 since Dutch elm disease hit the area in 1978.

Dutch elm is caused by a fungus that ultimately kills the tree. The only recourse is to remove the tree, Kiesz said.

The city plants about 200 replacement trees in rights of way each year, in addition to 150 to 200 trees in front of new homes.

The goal of the replacement trees is to fill in gaps where trees were removed, Kiesz said.

Treatment

When emerald ash borer is found, trees can be treated. But Kiesz doesn’t recommend that until the beetle has been found within 10 miles town.

Josten said the cost of treatment, which is injected into a tree, is $100 to $150. It needs to be done every two years.

Emerald ash borer has been found most recently in Manitoba, Canada, in 2017 and Nebraska in 2016, according to data compiled by the U.S. Department of Agriculture.

In Aberdeen, it will probably show up first at Wylie Park, Kiesz said. The city has traps covered in pheromones hanging at the campground.

The beetles can fly as far as 6 miles. They also migrate from town to town in firewood or on vehicles.

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Signs of emerald ash borer

• Adult beetles will start by eating leaves near the top of the tree.

• Larvae will burrow under the bark and dig S-shaped tunnels.

• Adult beetles will exit leaving D-shaped holes in the bark that are about 1/8-inch wide.

• Damage will start at the top of the tree and work down.

• Increased woodpecker activity on a particular tree might be a sign of infestation.

• For additional information, go to sdda.sd.gov/conservation-forestry/forest-health/emerald-ash-borer/.

Source: City Forester Aaron Kiesz and the South Dakota Department of Agriculture

Tree species in Aberdeen boulevards

• Ash: 37 percent.

• Hackberry: 9 percent.

• Linden: 8 percent.

• Maple: 7 percent.

• Crabapple: 6 percent.

• Honeylocust: 4 percent.

Source: City Forester Aaron Kiesz

Planting trees

City Forester Aaron Kiesz said a list of trees that are recommended for planting in rights of way is available at the Parks, Recreation and Forestry Department Office in the Aberdeen Recreation and Cultural Center, 225 Third Ave. S.E., or online at aberdeen.sd.us/DocumentCenter/View/91.