There’s bad news for arbor-enthusiasts in Georgia: the emerald ash borer has been spotted. Trust me. That’s pretty scary if you know what it means.
The emerald ash borer is a tiny little beetle that, although native to Asia, has a gigantic effect on North American ash trees. It’s killed millions of trees across Canada and Midwestern United States since it was first detected in 2002, and it really hasn’t looked back. Researchers have been on the lookout for this invasive species. In July they found some specimens in traps in DeKalb and Fulton counties, and later found confirmation that the beetles had, indeed, invaded.
This isn’t really the kind of beetle mania my parents told me about.
The emerald ash borer, or EAB, is devastating to North America’s indigenous ash species. A tree, when you think about it, is mostly dead. In between the bark and wood inside is a thin layer of something called phloem, which is the alive and growing part of the tree. Phloem is super tasty for the EAB larvae. When larvae burrow around in squiggly tunnels, just chomping away at the phloem, this is a major problem because the phloem is responsible for the transfer of nutrients from the ground to the top of the tree.
Dr. Rodrigo Mercader is an assistant professor of biology at Washburn University and has been studying the emerald ash borer since 2008. He said that as the phloem is destroyed, so is the tree’s ability to feed itself.
“It if ate the leaves, it’d be wonderful because most trees can handle even a couple years of every single leaf being killed. But if you kill that little section that feeds the tree? Dead,” he said.
The main problem with combating the EAB is that we have a hard time figuring out where these suckers are; they are surprisingly difficult to pin down. Part of the problem is that it takes a pretty long time to see signs of stress in infested trees. Dr. Mercader said it can take four to six years to see any indication that something might be wrong.
Then there is the issue of the life cycle of the EAB. If the beetle infests an already stressed tree, the beetle can mature in a year. If the tree is healthy, it can take closer to two years. However, research indicates that, as you go north into colder climates, there will be more two year life cycles. This suggests that as we go to the warmer south, we’ll see more one year life cycles. The result is that we may see a different development pattern in Michigan – where the EAB was first detected in 2002 – and in Georgia.
It’s also hard to predict where the EAB will turn up next. While the beetle can only travel about a kilometer a year, their most effective form of travel is just to hitch a ride with humans. The emerald ash borer can live in the wood of ash trees, so if you cut down and transport the wood to a new location, you’ve also introduced the EAB into that environment. When this happens, we see isolated clumps of EAB infestation. Over time, those clumps grow together and suddenly the map is covered in beetles. This is one reason why you should use local firewood.
This isn’t just a matter of saving trees. Ash is a popular tree used in landscaping, so as the trees get eaten up, property values go down. In addition, there are indications that as there are deleterious health effects associated with the loss of trees to the emerald ash borer.
There are, however, things we can do locally to slow the spread of the beetle. There is research being done into biological control via Chinese wasps that lay eggs inside EAB larvae and eggs and eat the beetles from the inside out. There is also a method called slow ash mortality. The idea is to treat some trees and not others to slow the spread of the infestation. For example, instead of treating every ash tree with pesticides, cities might treat a few trees with pesticides in the hopes that it could keep the EAB population under control. In addition, ash trees can be girdled. This means that the bark is stripped from a portion of the tree, which artificially stresses the tree. Because the EAB likes to attack stressed trees, a girdled ash will attract the female beetles to lay eggs. When that happens, the tree can be destroyed, thus destroying that community of beetles.
Unfortunately, this is quite an expensive problem to solve.
“In some cities that we’ve looked at to do some economic models, it costs $800 to cut down a tree. Say you have a million trees in a city. You have a problem,” said Dr. Mercader.
This is indeed true in Georgia, where there are 2.9 million ash trees planted around homes, businesses, parks and on public right-of-ways that are estimated to be worth $725 million. You can see why this is cause for concern.
The key is detection. If you suspect you have an infestation, it should be reported immediately.
Photo Credit: U.S. Department of Agriculture