If you haven’t heard the initials EAB, sooner or later you will. No, they don’t stand for the latest pop super group or a new, hot club you simply MUST get into. Rather, EAB stands for the Emerald Ash Borer. If you’re in an area that has a large number of Ash trees, unfortunately it’s a fairly safe bet that the EAB is heading your way.
The Emerald Ash Borer, Agrilus planipennis Fairmaire, is an exotic beetle that was first discovered in southeastern Michigan, near Detroit, in the summer of 2002. It probably arrived in the United States on solid wood packing material carried in cargo ships or airplanes originating in its native Asia. It has spread to numerous US States, since then. The latest documented find was in Louisiana, in the winter of 2015. Despite the fact that it feeds only on Ash (trees in the genus Fraxinus), the EAB is considered to be the most destructive forest pest ever seen in North America.
The adult beetles nibble on Ash foliage but cause little damage. Adult beetles are metallic green and about 1/2-inch long. They leave a D-shaped exit hole in the bark when they emerge in the Spring. The larvae (the immature stage) feed on the inner bark of Ash trees, disrupting the tree’s ability to transport water and nutrients. It is the larvae that do the damage which eventually kills an afflicted tree. EAB larvae are creamy white and slightly flattened, with a pair of brown pincher-like appendages on the last segment of their bodies. Their size varies as they feed and grow under the Ash tree’s bark. Full-grown larvae average 1.5 inches in length. They wind back and forth as they feed, creating S-shaped patterns called galleries under the bark. Larvae will feed under the bark for one or two years and can survive in green wood, such as firewood, as long as the bark is attached. In autumn, after one or two years of feeding under the bark, larvae will create a chamber for themselves in the tree’s sapwood. They stay in this chamber over winter and pupate in the spring, turning into adults. The beetles emerge from the tree, completing the life cycle. The pupae, like the larvae, cannot be seen unless bark is pulled away from the tree. Woodpeckers like to eat EAB larvae; thus heavy woodpecker damage on Ash trees may be a sign of infestation.
EAB has killed millions of Ash trees in southeastern Michigan alone, with many more lost in the areas it has spread to. The cost to municipalities, property owners, nursery operators and forest products industries, due to EAB infestations, now runs into the tens of millions of dollars. Regulatory agencies and the USDA have now enacted, and enforce, quarantines and fines to prevent potentially infested Ash trees, logs or hardwood firewood from moving out of areas where EAB occurs.
The good news is that several insecticide options are available to effectively treat landscape Ash trees threatened by EAB. Keep in mind, however, that insecticide control of insects that feed under the bark has always been challenging. This is especially true with EAB because most of our native North American Ash trees have little natural resistance to this pest. Effective control of EAB requires some care when selecting an insecticide product and application method to ensure the product is applied at the proper rate and time. Thankfully, research continues, and we are now far more capable of fighting EAB than we were when it was first discovered.
In the Summer of 2014, the Arkansas Agriculture Department and USDA’s Animal and Plant Health Inspection Service (APHIS) announced that EAB had been discovered in five counties in southwest Arkansas, bringing this pest only one county away from Texas. Because it is getting so close to Texas, it is wise to consider what impact EAB might have on our state.
The good news is that almost certainly the economic impact of this pest in Texas will be less than its impact in other states like Michigan and Ohio. That’s because Ash is less frequently planted here, and it makes up less of the native forest canopy, compared to the Midwest. In East Texas, where most Ash is located, less than 2% of the forest canopy consists of it. Fewer trees generally means less economic damage, and lower visual impact to city streets.
Some surveys done on Ash Trees in Texas show an average Ash percentage on urban streets of around 14% with a few parks reaching 30-40%. Unfortunately, in Austin, we have an Ash community that stands at around 17% of our urban forest. Compare these numbers with Ash numbers in Iowa (average of 16.5% of urban trees, some communities up to 87% Ash), Pennsylvania (14% of all trees). Even Colorado reports Ash composition of city trees at between 15-25% of all shade trees. In the Chicago area, where EAB has hit hard, 12% of city trees are estimated to be Ash, and about 15% in Minneapolis.
In Texas’ favor, as mentioned above, is that there has now been over ten years of research on control of EAB; and some effective treatments are available for at-risk trees. The most effective treatments are systemic insecticides which can be applied to the base of the trunk, or injected, or sprayed on the bark. These insecticides include emamectin benzoate, imidacloprid, and dinotefuran. There is even a naturally-derived treatment, azadirachtin, that can protect trees for up to a year.
David Smitley, Michigan State University entomologist, reports that in 2010, the city of Midland injected all Ash trees felt to be worth protecting (about 50% of the Ash in the city) with emamectin benzoate. Results exceeded expectations when all treated, and most untreated, trees survived. This contrasted with four other surrounding communities that treated lower percentages of their trees. Although treated trees were well protected, nearly all the untreated (control) Ash trees in these other communities died within four years. Smitley attributes the high survival rate of the untreated control trees in Midland to beetle populations crashing from exposure to the high number of treated trees (adult beetles feeding on leaves of a treated tree will die). Once a city stops an EAB outbreak with mass tree treatment, and enters a maintenance phase, experience shows that Ash trees should not need to be treated more than once every 2-3 years.
Texas Forest Service urban forester, Courtney Blevins, doubts whether most Texas cities will opt to treat because Ashes are not widely planted as shade trees here. Most of the Ash Trees in the Austin area are Arizona Ash, and were planted 30-40 years ago. This species is no longer favored in Austin. The greater impact will likely occur in the native Texas forest, where stately ash trees add to the diversity and beauty of the East Texas woods.
The preceding may be of little consolation to you if you have a valued Ash tree in your yard. If this is the case, there are good treatments, as above, should you decide to protect your tree. You can rest a bit easy, though, since there is no need to worry about treating your tree(s) until EAB is confirmed within 10-15 miles of your home.
Monitoring for EAB continues throughout East Texas in 2015 as part of an APHIS-funded survey.
Do your part to keep Texas EAB-free: DO NOT BRING FIREWOOD INTO TEXAS!!!
Buy Local, Burn Local. Keep EAB out of Texas!
If you suspect that you have EAB, contact the Texas Department of Agriculture at 1-800-835-5832 or USDA at 1-866-322-4512.