It’s hard to believe that something the size of a small beetle can have such a devastating effect on millions of trees. Such is the case with the emerald ash borer, responsible for the destruction of over 30 million American and Canadian ash trees.
Native to Asia, the emerald ash bore (EAB) was first discovered near Detroit, Michigan in 2002. Upon investigation, after a wave of reported dying ash trees, scientists at Michigan State University discovered tiny insects living behind the bark of these trees. They were no larger than a grain of rice, had a metallic green sheen to them, and were unlike anything they had ever seen. The EAB was finally identified with the help of an eastern European entomologist expert, and it was theorized the insect was transported here from China in the 1990s in wooden crates.
The EAB larvae feeds on the bark of the tree, tunneling deeper and deeper. As they feed, they actually injure the plant’s circulatory system, inhibiting the tree’s ability to transport nutrients and water throughout, and eventually killing the tree within one to three years. Take that single tree and multiply it by an entire forest, and then an entire state to truly appreciate the devastation this killer can inflict. Millions of trees throughout Canada and the Midwest have fallen victim, now many feel it is only a matter of time before it makes its way to Minnesota.
Jacob Ryg, city forester in Rochester, emphasizes that 17,000 of the trees lining the streets and adorning the parks in Rochester alone, are ash. The bill to remove the dead trees and plant new ones would be huge, with an estimated $27 million just in Minneapolis. When they do arrive, and start feasting on Minnesota’s over 872 million ash trees, they will have a veritable buffet of ash species that were initially planted to replace victims of the former Dutch Elm disease.
The EAB is an aggressive killer. Once the larvae becomes an adult, they emerge, fly to another tree and lay eggs there, and the cycle continues. There is not much to be done to prevent the inevitable spread, but it is possible to slow it down, and provide researchers the necessary time to find more effective ways of destroying the beetle. The U.S. Department of Agriculture has restricted movement of firewood, ash trees and ash tree parts from known infested areas. If the EAB is left to its own resources, its spread will be limited to a short distance each year.
Only ash trees are at risk from the beetle.
An adult beetle is metallic green in color and about 1/2 inch long.
Woodpeckers love EAB larvae; a sign of infestation is woodpecker damage on ash trees.
The adult beetles leave a “D” shaped hole in the bark when they exit the tree. As larvae gets bigger, they leave winding track marks on the wood.
Firewood cannot be moved in many areas of Michigan, Ohio, Illinois, Indiana, Pennsylvania, West Virginia, Maryland, Ontario and Quebec because of the EAB quarantine (Michigan, Illinois, Indiana, Maryland, Minnesota, Missouri, Ohio, Ontario, Pennsylvania, Virginia, West Virginia, and Wisconsin)
Treating Your Ash Tree: If you discover signs of EAB, there are several insecticide options available, however not all are consistently effective. If a tree has lost more than 50 percent of its leaves then it is probably to late to save it. The treatment is harsh, and the tree needs to be healthy enough to survive its effects and carry the insecticide up the trunk into the branches and leaves. Once you initiate treatment, the leaves may appear to be thinning out, but after the second year, when the tree has had a chance to heal, it may return back to a healthier state.
Methods of treatment include insecticide injections into the soil, trunk, lower trunk sprays, or cover sprays applied to the trunk, main branches and possibly the foliage. It is a good idea to seek professional help when dealing with EAB to ensure you are using the correct treatment for your tree.
The most effective product to date, and known to protect the tree for one full year, is Emamectin benzoate.
Your tree may not exhibit any symptoms of EAB, but may be quarantined due to infestations in the surrounding area (within 10-15 miles). In that case, it is not too early to begin treatment.