Editor’s note: This is the first of two columns addressing the emerald ash borer.
Last month, the presence of the emerald ash borer in Shawnee County was confirmed at Lake Shawnee. This invasive pest is a killer of ash trees. It is to ash trees what Dutch elm disease was to elm trees in the 1960s-70s, when many communities lost all their shady, elm tree-lined streets and parks to the disease.
Ironically, ash trees were the tree of choice to replace the elm trees lost to Dutch elm disease.
The emerald ash borer attacks all ash trees, from nursery stock to healthy mature trees. It attacks all varieties of ash trees, except mountain ashes, which aren’t true ash trees. It appears to attack only ash trees.
Since its discovery in 2002 in southwest Michigan, the borer has killed millions of ash trees in the Great Lakes states. The pest’s spread has been aided by the interstate movement of infected nursery stock — moving infested logs to saw mills and, more recently, by unsuspecting campers transporting infested firewood to non-infested areas.
It’s now found in northeast Kansas, most states east of Kansas and all of our border states.
The emerald ash borer is a native of Asia and likely arrived in the United States in wood used in shipping crates for transporting goods from China. It is a small metallic-green beetle, about 1/2-inch long and 1/8-inch wide. It hibernates as pupae under the bark of an infested tree until it emerges as an adult emerald ash borer May through July.
The female lays eggs in the crevices of the ash tree bark. The eggs hatch in seven to 10 days, and the larvae bore through the bark and into the cambium layer of the tree. As the larvae eat their way — making S-shaped tunnels in the cambium — they cut off the flow of nutrients to and from the top of the tree to the roots.
As a result, the top branches of the tree, called the canopy, start to die. This is usually the first sign the tree is under attack by the emerald ash borer. Other signs include increased woodpecker activity, because the birds seek out the borer larvae and adults; D-shaped holes in the bark as the adult borers bore their way out of the tree; leafy sprouts at the base of the tree; and vertical splits in the bark.
Depending on the level of infestation, the tree likely will die in one to three years. However, note that drought, diseases and other insects also can kill ash trees. If you see ash trees with these symptoms, call the Kansas Department of Agriculture at (785) 862-2180 for guidance.
The record for successful insecticide use for saving an ash tree from the emerald ash borer is spotty. Some efforts have shown success with up to 99-percent reduction in the number of emerald ash borers in treated trees as compared to untreated trees in the same area. However, all researched treatment efforts indicate an ongoing annual, biannual and maybe eventually triannual treatment program will be necessary.
Also, some early research indicates that with some treatment techniques, the emerald ash borer population continues to increase in treated trees, although at a slower rate. Therefore, the techniques may be only delaying the inevitable loss of the tree.
For most cities, the solution has been to remove dead and dying ash trees. However, ongoing research is showing enough progress that some communities now are trying systemic insecticide treatment efforts as a cost-effective option to removal and disposal of diseased ash trees.
A home treatment option and chemicals are available. But considering the lower effectiveness and the legal limitations on home treatment efforts, homeowners should carefully consider the ongoing cost versus the likely success of the efforts.
Professional tree specialists have better equipment, greater access to more effective chemicals and fewer restrictions to successfully treat ash trees for the emerald ash borer. Homeowners need to consider the value of each ash tree versus the cost of removal or ongoing cost of treatment, which may or may not save the tree.
In any case, research shows that when half of the tree has died, there is little likelihood any treatment can save it.
Here’s some timely advice from the experts. First, the obvious: Don’t plant ash trees. Second, if someone guarantees that they can protect your ash tree, hold on to your wallet.
Ed Dillingham is a Shawnee County Master Gardener.