More than 12 years after it was discovered in southeastern Michigan, the emerald ash borer (EAB) is still wreaking havoc on the rapidly shrinking ash tree population in North America.
As of last month, EAB had been confirmed in 24 states (Arkansas, Colorado, Connecticut, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Massachusetts, Michigan, Minnesota, Missouri, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin) and two Canadian provinces (Ontario and Quebec). Iowa and Indiana in particular have been hit hard recently by the pest.
So far, EAB has killed tens of millions of ash trees and threatens to kill most of the 8.7 billion ash trees throughout North America. It is estimated that EAB will have caused $10 billion in economic damage by 2019. It is now considered the most destructive forest pest ever seen in North America, according to www.emeraldashborer.info.These facts are staggering, but it’s likely they’re not unfamiliar to tree care professionals.
What you may not know is that the methods for controlling EAB are growing in number, sophistication and effectiveness.
“We have progressed and learned things [since 2002],” said Dr. Deborah G. McCullough, a professor in the entomology and forestry departments at Michigan State University and one of the country’s foremost experts on EAB. “Now there’s no reason for a landscape ash tree to die if someone is willing to take care of it. We have really effective products now. We’ve learned it’s much more cost effective to treat trees rather than replace them.”
When an ash tree is attacked by EAB, the canopy begins to thin above infested portions of the trunk and major branches because the borer destroys the water and nutrient conducting tissues under the bark. Heavily infested trees exhibit canopy dieback, usually starting at the top of the tree. One-third to one-half of the branches may die in a year. Most of the canopy will be dead within two years after symptoms are first observed.
As cities and states first had to deal with EAB, removing and sometimes replacing infected trees was common practice. That has changed over the years, according to McCullough.
“A number of municipalities, instead of just waiting for their ash trees to die, have relatively comprehensive management plans to deal with their ash trees and EAB,” McCullough said. “They have a good inventory, have picked out trees to treat with effective insecticides, and removed some of the trees that needed to be removed. That situation has changed hugely from where it was three or four years ago.”
According to Dr. Clifford Sadof, professor of ornamental pest management at Purdue University and an EAB expert, the methods for fighting and controlling EAB are becoming more efficient, more sustainable and more consistent.
“Good arborists and pest managers always want to find the problem before [they develop] a plan of attack,” Sadof said.
Regarding that plan of attack, Sadof, who is speaking about EAB next month at the New England Grows convention and expo in Boston, pointed out several relatively, noteworthy ways to fight EAB:
Mobile app: Purdue University has developed a mobile app (available for purchase in the iTunes and Google Play stores) called the Purdue Tree Doctor. This app helps people better identify and manage insects and diseases, such as EAB.
Arborists can use this app in the field to identify tree problems by matching damaged plant parts to over 1,000 high-resolution photos. They can then check diagnoses with detailed descriptions of damage and stages of problem development linked to each photo. Information can be searched by tree or by pest, with over 60 trees and 175 pests included in the app’s database. “It’s a cheap tool to have in your pocket,” Sadof added.
Inventory management: Sadof stressed the idea of keeping an accurate and up-to-date inventory of trees in a given area or system. “Do an inventory to find out what the scope of your problem is,” Sadof advised. “Good arboriculture relies on accurate and current inventory of trees. The best defense [of EAB] is having an accurate inventory and keeping track of what you have.”
One way to create an organized and useful tree inventory for the purposes of managing EAB is by using Purdue University’s EAB Cost Calculator, which can be downloaded for free at http://extension.entm.purdue.edu/treecomputer/index.php. This free Web-based calculator allows users to input tree categories based on size and class, which then projects growth in trees over time, the cost of treating trees, removing trees, and replacing trees over a 25-year period.
The cost calculator is driven by an EAB invasion wave model that assumes it takes eight years for EAB to kill all the ash trees in a given city after it has been detected in a given county. Essentially, you can stage your response to an EAB invasion based on the percentage of ash trees that are dying.
Insecticides: Insecticides that can effectively control EAB fall into four categories: systemic insecticides that are applied as soil injections or drenches; systemic insecticides applied as trunk injections; systemic insecticides applied as lower trunk sprays; and protective cover sprays that are applied to the trunk, main branches and (depending on the label) foliage.
Life cycle of EAB
- The beetle can have a one or two-year life cycle.
- Adults begin emerging in mid- to late May, with peak emergence in late June.
- Females usually begin laying eggs about two weeks after emergence.
- Eggs hatch in one or two weeks, and the tiny larvae bore through the tree’s bark.
- The larvae feed under the bark for several weeks, usually from late July or early August through October.
- The larvae typically pass through four stages, eventually reaching a size of roughly 1 to 1.25 inches long.
- Most EAB larvae overwinter in a small chamber in the outer bark or in the outer inch of wood.
- Pupation occurs in spring and the new generation of adults
will emerge in May or early June to begin the cycle again.
According to Sadof, the use of products that have emamectin benzoate as the active ingredient have become the most successful and reliable way to fight EAB in terms of trunk injections. This approach requires puncturing or drilling the holes, which can cause internal damage to the trunk. The most tested of these products, according to Sadof, is TREE-äge, a product made by Arborjet. McCullough called this product a “game-changer” when it received expanded label approval by the Environmental Protection Agency a few years ago.
Sadof also pointed to a relatively new product called ArborMectin, which also has emamectin benzoate as the active ingredient and is used for two-year control of key pests, including EAB. Another product, TreeAzin, is listed by the Organic Materials Review Institute (OMRI) for use in organic crops and has azadirachtin as its active ingredient and was developed by the Canadian Forest Service in collaboration with BioForest.
“There a lot of new products coming down the pike,” Sadof said.
Webinars: Educational webinars are held throughout the year; you can find the dates and times on www.emeraldashborer.info (click on Publications/Resources and then Educational). Past webinars, hosted by experts with extensive knowledge of EAB, can also be accessed on the website.
According to Sadof, since the webinar series started in 2009 there have been more than 3,000 attendees and 30,000 downloads. The webinars can also be used for certification credits (see the website for more details). “It gives people the ability to stay updated without leaving your desk,” Sadof said.
Along with this constantly growing list of EAB treatment options, experts are doing extensive research to acquire more knowledge of EAB, with the ultimate goal of winning the fight against it.
“There’s still so much about EAB we don’t know,” McCullough said. “But studies are being done. We are working on differences among ash species in terms of their resistance and relative attractiveness to EAB. There’s lots of work going on related to population dynamics, spread and dispersal, and how fast EAB moves. We’ve also been able to use tree rings taken from dead ash trees across a 5,800-square-mile area to show where EAB got started in North America … to show it was actually here in the 1990s.”
Online Resources for EAB information
Official page: www.emeraldashborer.info
Society of Municipal Arborists: www.urban-forestry.com/emerald-ash-borer
Insecticide options for protecting ash trees fact sheet: www.emeraldashborer.info/files/multistateEAB_ InsecticideFactSheet.pdf
Research: Emerald Ash Borer May Have Spread to Another Tree: www.entomologytoday.org/2014/10/10/emeraldash- borer-may-have-spread-to-different-tree/
Emerald Ash Borer University www.emeraldashborer.info/eabuniversity