Plant Palette

Plant Palette

Emerald Ash Borer Update

Photo of Jennifer Schultz Nelson

Jennifer Schultz Nelson
Extension Educator, Horticulture
jaschult@illinois.edu

Many of you may remember back in 2006 when the news came that the Emerald Ash Borer (EAB) had been found in Kane County, in Northern Illinois. This tiny green insect is responsible for the death of more than 20 million ash trees. This summer, the pest has been confirmed much further south, in Chenoa, Illinois, north of Bloomington.

EAB is native to Asia, specifically eastern Russia, China, Japan, Korea, Mongolia, and Taiwan. It was discovered in Detroit, Michigan in 2002. Experts believe it was present in Detroit at least ten years before its discovery, and that it entered the U.S. via solid wood packing materials.

The way EAB attacks typically results in the top of the tree dying first. The EAB's life cycle occurs over one year. They can only survive on ash trees (Fraxinus spp.). Adult beetles are about half an inch long and emerge from under the bark of infested ash trees in May through early August. They leave a tiny hole, only 1/8" long, in the shape of an upper case letter 'D'. The flat side of the 'D' is always parallel to the ground. Adults feed sparingly on the tree's foliage until they mate. The female deposits eggs on the ash tree's bark.

Scientists have observed the beetles infest a new ash tree at the top first, making early detection difficult. It may take 4 to 6 years of infestation before visual symptoms such as die back are observed.

The damage the EAB larvae do unseen under the ash tree's bark is what leads to dying branches and ultimately the tree's death. Because of larvae eating their way through the phloem, the tree loses its ability to pump food above the damaged areas. Without food, the part of the tree above the larval damage dies. Since infestation commonly occurs at the top of the tree, dieback starting at the top of the tree is most often observed. As larval numbers and damage increase, so does the proportion of the tree that dies.

Another symptom of EAB is called epicormic growth. This type of growth produces prolific clusters of thin stems emerging from larger diameter branches and the trunk. It is a last ditch effort for the tree to stay alive.

What does this mean for homeowners in and around Macon County? Will we see EAB anytime soon? Time will tell—it is very likely that at some point it may be found here. If you have questions as to whether Emerald Ash Borer is affecting your ash tree, call our office at 877-6042 or 877-6872. We can help determine whether your situation warrants a call to the Illinois Department of Agriculture for further investigation.

If Emerald Ash Borer is truly suspected, it is a very serious situation that would elicit response from several government agencies and likely place a quarantine on the county.

No one, even a professional, should casually conclude a local tree has Emerald Ash Borer just because an ash tree has some dead branches or suspicious growth. It is a very serious diagnosis, and if it is truly suspected, it needs to be investigated ultimately by the Illinois Department of Agriculture.

Scientists are scrambling to research possible control measures for Emerald Ash Borer. Keep in mind that scientists only have 6 years worth of data for this pest. EAB is not a pest in Asia. No one paid much attention to it before it began its destructive path across the U.S.

There are insecticidal treatments for EAB that may be effective in preventing EAB infestation or eliminating early infestations. These may be applied as a soil drench by the homeowner or professional, or injected into the tree by a professional. The active ingredient imidacloprid is in Bayer Advanced Tree and Shrub Insect Control, the only treatment currently available for purchase by homeowners.

This does not mean that you should run out and start treating your ash trees for EAB. There are some important factors to consider before deciding to treat trees for EAB:

Treatment is not recommended unless EAB is found within 15 miles of a given tree.

Insecticide treatment appears to be most effective on trees less than 10 inches in diameter

Insecticide treatments can be expensive, and need to be applied each year indefinitely

At least 2 years of treatments are needed before insecticides offer 'good' protection

Researchers do not know how long treated trees will survive

The only certain method to control EAB is to remove the tree

The question of using insecticides to treat EAB is not going away anytime soon. While scientists have found some promising chemicals to wage war against EAB, their long term effectiveness is unclear. The expense alone is enough to discourage many homeowners. Costs may run from $60 on a newly planted tree to hundreds of dollars for a mature tree-- and remember, this cost is per year, not a one time shot. Consider also the fact that with each treatment, more insecticides are released into the environment.

If you are planting new trees in your landscape, I highly encourage you to choose a tree other than an ash. If you already have an ash tree, consider planting a replacement tree nearby to get a jumpstart in the likely event that your ash tree will need to be removed. Some homeowners and municipalities are proactively removing ash trees from their landscapes. The choice is yours.

There is up-to-date information available about Emerald Ash Borer at www.IllinoisEAB.com and www.emeraldashborer.info.

View Article Archive >>