BROOKINGS – At first glance, it’s just an emerald green beetle, much smaller than even a penny. The diminutive size shouldn’t fool anyone, however. This beetle is currently causing havoc throughout much of the Midwest.

Known as emerald ash borer, this invasive species is slowly devasting the ash tree population in North America – one community at a time. 

What is emerald ash borer?

Emerald ash borer (EAB) is a jewel beetle, native to northeast Asia. Scientists believe that the beetle arrived in the U.S. in the 1990s, traveling aboard cargo ships. EAB was first identified in Michigan, and it was quickly found that the insect was highly destructive toward ash trees, which populated Michigan forests.

“(EAB arrived) in the Detroit area. It appears to have come in on dunnage, which is wood that helps hold shipments in place,” explained John Ball, SDSU Extension forestry specialist and South Dakota Department of Agriculture forest health specialist. “Nobody noticed it until 2002. They just noticed ash dying.”

In China, the insect fed on ash trees. However, ash trees in China and the rest of northeast Asia had developed a defense mechanism that allowed the tree to survive the insect’s infestation. In the U.S., ash trees have no such mechanism. 

“Our ash trees, the ones native to North America, do not have any defensives against it,” Ball said. “In Asia, the only time it is able to kill a tree is when it is weak.”

Ball explained that when scientists first discovered dead Ash trees, they were hardly surprised. However, when they identified EAB in Michigan, it was the first time the bug had been seen outside of northeast Asia.

EAB kills ash trees by cutting off the food supply of the tree. During June and July, female EAB lay eggs on the tree. The eggs hatch within a couple weeks, and the worm – the larvae – feed underneath the bark. This lasts until late fall, and then the larvae emerge as adults around June 1, Ball explained. 

“Every year the population gets a little bit bigger in the tree, and their tunneling beneath the bark actually severs the connection between the leaves that make the food and the roots that need the food,” Ball said. “The tree essentially starves to death.”

It takes a few years for EAB to kill off a single tree, but once it does, the trees become weak and brittle – susceptible to falling over at any minute.

“In the beginning, and I can remember the headlines, a tree fell on a bus and killed a number of people and trees have fallen on cars and houses and people,” Ball said. “It’s not like the elm trees that die from Dutch elm disease and stand there for a while. These become very brittle.”

While the state of Michigan does not track ash tree (or any tree) related deaths, between 2016 and 2018, the Lansing State Journal reported that 14 people had died from crashes with dead ash trees. 

First appearance in South Dakota

EAB was first discovered in South Dakota in 2018, near Sioux Falls. However, Ball said the research done after first discovery shows that EAB had likely been there three years earlier.

In South Dakota, EAB has currently only been identified in Lincoln and Minnehaha counties. In 2020, it was found that Canton had an EAB infestation, but the bug had been attacking the ash trees for three or four years before that, Ball explained.

“It is wiping out (Canton’s) ash at a much faster pace than they are in Sioux Falls because Canton is a smaller town,” Ball said. The beetle, which flies around during the day, can only travel short distances on its own, making smaller towns more susceptible to quicker, thorough infestations.

Currently, EAB has not been identified in any other counties in South Dakota outside of Lincoln and Minnehaha. In Minnesota, EAB has been confirmed near Worthington, New Ulm and Albert Lea, amongst many other cities and counties. 

Brookings’ future

“It will kill every (ash) tree,” Ball said. “None will survive.”

If that sounds like a doomsday scenario it’s because it is. Ball explained that EAB has gone through thousands of communities and 35 states, all with the exact same results: devastation.

It is very difficult to predict when an EAB infestation will happen, but based on research done in the area, Ball said that in 2018, when Sioux Falls had their initial EAB discovery, he felt that Brookings could have an infestation in five to seven years. This would put the timeline for identification at some point during the summer of ’23, ’24 or ’25. Of course, with the unpredictable nature of EAB, it is entirely possible that it could already be in the community and/or identified this summer.

Ball explains that, for example, the summer EAB is discovered in Brookings, it can be assumed it will have been in town for “two or three years” before, but the population will have been small enough that no one will have noticed.

“Usually within 10 years of identifying it in a town, all the ash (trees) are dead,” Ball said. “It happens very quickly.”

Ash trees will then become a shrub, in alleyways and side yards, as the trees will survive just long enough to drop seeds before succumbing to EAB. 

Ball notes that once EAB is identified in Brookings, it will always be in Brookings. 

What can be done?

While EAB can – and will – have devastating effects on ash tree populations, there is some hope for the survival of some ash trees. 

Currently, the U.S. Department of Agriculture is working on a “biological control” for EAB populations. 

Per the USDA, “Biological control aims to control a pest by introducing its natural enemy or predator. Biological control has been used successfully for over 100 years in the United State to control other pests, too.”

The biological control that is currently being developed is the introduction of stingless wasps – mortal enemy to EAB larvae – to control the growing population. There are currently four different species of wasps being developed as biological control agents.

“So far, at least one of four wasps have been released in 30 states and their offspring have been recovered in 20 states, which means the wasps are establishing, reproducing and, more importantly, attacking and killing EAB,” according to the USDA.

Other things that can be done involve the use of chemicals to treat EAB infected trees.

“When I say every ash will be dead, that’s every ash that isn’t being treated,” Ball said. “There are very effective chemicals to treat for EAB.”

Does this mean that people should start treating their ash trees as a preventative measure?

According to Ball, people with ash trees should wait to start treatment until after infestation begins or at the very least, until EAB is identified in the county. 

What is being done now?

Ball explained that cities take different approaches to EAB infestations. For example, the City of Sioux Falls is actively removing both dead and healthy ash trees throughout the city. 

The City of Brookings has taken several steps over the past few years to prepare for an EAB infestation. The first step taken, according to Dusty Rodiek, Parks, Recreation and Forestry director for the City of Brookings, was to create a EAB management plan, which was done a few years.

The department has also been strategically eliminating poor quality ash trees in the city over the past five years. Notably, 25 ash trees were removed at Hillcrest Park in March 2020 partly to prepare for a future EAB infestation. Poor quality ash trees have also been eliminated at other parks and other city-owned property, including Pioneer Park in the winter of 2021.

“Some of them were safety hazards, and they were just of a poor quality that those would be the type of trees that EAB would start taking hold. Those are the types of hosts that they are looking for,” Rodiek said. “We’re trying to proactively eliminate what are going to be some potential hosts.”

The Urban Forest Initiative that the department is sponsoring for a second year is in-part in anticipation of an EAB infestation. By planting trees now, the city is helping to prepare for the EAB’s inevitable devastation of ash trees in the city.

Ball explained that in recent years, there has been a push to plant maple trees to replace the dying ash. Ball remembers a time when the Dutch elm disease outbreak was occurring and there was a push to plant one specific type of tree: ash.

“My concern there is, we are just going to end up panting a lot of maple, and sooner or later, a pest is going to come in and kill them,” Ball said. “The country with the most species of maple is China.”

Dutch-Elm disease originated in China, as did EAB, so the fear is that there could an insect in China that feeds on maple trees.

“We’re not saying no to maple. We’re just saying we need to diversify,” Ball explained. “We need to plant a lot of different species and not just say, ‘OK, well let’s plant maple, that’s another fast-growing tree.’”

Rodiek said that the department has been keeping an eye on the ash trees – and all trees for that matter – on city-owned property, looking for potential EAB infestations. Last year, on someone else’s property, there was a possible EAB infestation that the department was called to, Rodiek said.

“As it turns out, that was a false alarm,” Rodiek said. “As of today, we still seem to be borer free.”

To know what to look for with an EAB infestation, the department staff have been trained on warning signs and treatment methods for the trees.

EAB warning signs

Identifying ash trees with an EAB infestation is not simple, but it can be done. The first way to possibly detect for EAB is to examine the tree’s canopy after the leaves have grown. A “thinning” canopy signals that the tree may be in the early stages of an infestation.

This is not an exact science because Brookings has a lot of dying ash, Ball said.

A second, and more obvious way to detect for EAB is when a “superman gallery” is visible underneath on the trunk of the tree underneath the bark. 

Superman galleries, what Ball calls them, are tunnels just beneath the bark that form an “S” shape. These are from the EAB larvae tunneling after infestation.

“That’s a very good indicator,” Ball said.

If an EAB infestation is suspected and a “S” shape is present, take a picture and email it to Ball at john.ball@sdstate.edu. If it looks close, Ball will come out and determine if it is an EAB infestation.

Those who suspect an EAB infestation can also call the city’s forestry division as well.

For more information on EAB in South Dakota, visit https://emeraldashborerinsouthdakota.sd.gov/.

Contact Addison DeHaven at adehaven@brookingsregister.com.