Correspondent
MADISON
Emerald ash borer (EAB) is a relentless but picky bug with a voracious appetite for ash that is changing planting plans across the eastern U.S. As the exotic beetle washes over the landscape, leaving dead trees in its wake, the need for planting diversity is underlined.
Ironically, ash was the replacement tree of choice when Dutch elm disease swept the country, Phil Pellitteri, University of Wisconsin Extension entomologist, said during the latest Wisline Brown Bag horticultural program. The useful, hardy tree is abundant in urban and forest settings, with some areas of Wisconsin nothing but ash, he noted.
Ash are valuable shade and production trees, whose strong, hard wood is used for timber, tool handles, baseball bats, veneer and firewood. They are also tasty, if you’re a Buprestidae, or EAB.
In a joint presentation with Dr. Robert Tomesh, UW Extension horticulture specialist, broadcast on Feb. 26 to UW Extension offices around the state, Pellitteri said it’s likely the metallic wood boring beetle snuck into the U.S. at the Port of Detroit. It seems to have been quietly destroying ash trees in Michigan for 10 years before it was discovered in June of 2002.
In August of 2008, EAB was found near Newburg in southeastern Wisconsin. In April of 2009, it was confirmed in western Wisconsin in Vernon County near the Mississippi River. It was caught in Crawford and Brown counties in July, and in Milwaukee County in August.
It was located in Minnesota in 2009. “The fight is on,” Pellitteri said. “The question is what can be done to slow the spread, because in the long run, it is going to be impossible to totally stop this insect.”
Anyone who suspects EAB should call their local Extension office for more information or the Department of Agriculture, Trade and Consumer Protection (DATCP) at 800-464-2803. “The trouble is when a situation like Michigan develops, where there are hundreds of square miles infested before diagnosing it,” Pellitteri said.
Reference material currently available includes an extensive site jointly supported by DATCP, Department of Natural Resources, UW Extension and others, located at emeraldashborer.wi.gov/.
The site covers where the bug has been found; the 11 quarantined counties and sawmills who work with EAB logs. It provides identification assistance, including look-alikes, and information for homeowners, communities, professionals and woodlot owners who have ash in their acreage.
Educational workshops are planned from 10:30 a.m. to 3:30 p.m. March 18, in Brown County at Liberty Hall in Kimberly; and from 12:30 p.m. to 4 p.m. March 24, in LaCrosse County Myrick-Hixon Eco Park.
Pellitteri explained that although there are other common metallic wood borers, such as birch borers and two-line chestnut borers, EAB is the first to strike ash, or Fraxinus trees. The metallic green beetles are a bit under an inch long, narrow, and look like a piece of jewelry, Pellitteri said. They emerge from late May to mid-June through distinctive, small, D-shaped holes in the bark.
The females lay eggs in the crevices of bark. Skinny, flat-headed, white larvae hatch in a few weeks and immediately burrow into the tree’s tissue where they chew serpentine trails that disrupt the tree’s circulatory system.
The frustrating thing about EAB, Pellitteri said, is that the bugs do not stick to stressed trees, as other borers do. “They attack healthy, happy trees,” he said, causing an abundance of green water sprouts as the trees fight for their lives, dieback and death within three years.
Unfortunately, the exotic beetle has few natural enemies. Woodpeckers enjoy them, so a tree with woodpecker activity might signal an EAB infestation.
The insects do not move very far under their own power. An adult could fly about one-half mile, Pellitteri said, but people can give them a lift. “That seems to be the story with infested states, with the bug coming in on infested firewood or logs,” he noted.
There are strategies to fight EAB, especially with high value ash trees, but protection is considered a high maintenance regime that must be performed annually.
One option is spraying the tree to kill adult EAB before they can lay eggs. The timing is critical for sprays applied in late May and early July. However, it is difficult to spray a large tree and most homeowners do not have the equipment, Pellitteri noted.
Systemics can be a better option. Chemicals are injected or sprayed on the trunk or applied to the root zone by watering. “We are seeing reasonably good response with systemics,” Pellitteri said, noting trees with 30 to 40 percent dieback have been saved.
Bayer Tree & Shrub Insect Control, with imidacloprid, is available to homeowners. The tree is measured, and the appropriate amount of product is mixed into a bucket of water and applied close to the trunk. Over time, the roots uptake the chemical and move it through the tree’s system. An application in the fall and again in the spring might be necessary, especially with large trees.
While systemic treatments are not a guaranteed fix, the data is quite promising and offers a way to save a high value tree, Pellitteri said.
Commercial arborists have additional options, including Tree-age with emarnectin benzoate, now backed by research data suggesting it lasts two or three years. Milwaukee is using this chemical on their boulevard trees, Pellitteri noted.
One of the biggest EAB concerns is how to handle the heavy mortality rates over a very short time. The best way in a forest situation is salvage, but the theories are still being worked out, Pellitteri said.
Since the bug lives just under the bark, the wood can be used for lumber, as long as it is debarked and the bark chipped, Pellitteri said. Infested wood can be burned as firewood or mulched if the size of the chips is small enough to stop the life cycle of the bug.
Be aware that although the normal life cycle is a year, EAB can survive a hostile situation for two or more years, Pellitteri noted.
Alternatives to ash trees include maples, Kentucky coffee trees, oaks and Turkish filberts. “We are now working toward a diversity in our landscape, so bugs can’t wipe out large populations”, Tomesh said, noting nursery catalogs offer the best chance of finding suitable replacement trees.
