Image courtesy David Cappaert – Michigan State University, Bugwood.org
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State Entomologist Robin Pruisner has good news for Iowans concerned about the movement of the emerald ash borer.
On January 17, The Iowa Emerald Ash Borer Team released the final results of its 2012 surveillance efforts; the results show little movement of the emerald ash borer (EAB) within Allamakee County, which remains the only county in Iowa where the pest has been found.
In 2010, EAB was found on Henderson Island in the Mississippi River, which is in Allamakee County. The results of the 2012 survey results show that EAB has moved off of Henderson Island but remains inside the county’s borders. Since 2010, Allamakee County has been under a federal and state quarantine prohibiting movement of firewood, ash timber, and other wood products that could further spread EAB.
What is an emerald ash borer?
The emerald ash borer (EAB) is a green, metallic beetle roughly half an inch long and 1/8 of an inch wide (think of a sunflower seed). Its back is flat and its underside is curved, giving the distinctive D-shape to its exit holes in ash trees.
The working theory is that it was accidentally introduced in the United States in Michigan from Asia, and has since spread from there.
How does EAB spread?
The female lays eggs in crevices of the tree bark; when the eggs hatch, larvae chew through the bark and start burrowing into the tree. Throughout EAB’s 4 larval stages, it eats through the ash tree’s active phloem and xylem (inner layers of the tree that transport water nutrients such as sucrose), effectively strangling the tree. Because each adult female lays between 60 to 90 eggs, the infestation can progress rapidly once
the beetle has put down roots. Normally The larvae spend the winter beneath the bark and feed for a short time in the early spring. At this point, EAB pupates and transforms into an adult. The beetle emerges from under the bark by chewing a D-shaped hole, usually June through late July with peak emergence expected in June. Adults fly to the top of the ash tree and feed on the leaves; approximately two weeks later the beetles
mate and begin the egg laying process. Once an ash tree is infested with EAB it will die within
2-4 years.
Why is EAB such a problem?
One of the reasons EAB has proliferated is because it is not native to North America, and its
natural enemies, both predators and parasitoids, were not brought from its native Asia when it was introduced. While all ash trees are susceptible to EAB, the insect will infest any ash tree, but prefers damaged or stressed trees.
In addition, EAB’s destructive behavior is not discriminatory, as Pruisner explains.
How can I prevent EAB from infesting my ash trees?
To determine if you have an infestation, check for D-shaped exit holes in the bark and S-shaped tunnels (called “galleries”) under the bark, which are made by the feeding larvae. Crown thinning and dieback, epicormic sprouting and woodpecker feeding are also signs of an EAB infestation.
Generally speaking, insecticide products work best as preventative treatments for healthy trees. If you have a tree with a 25-inch or less circumference (about 8 inches in diameter), you can treat it yourself for EAB using ISU Extension’s soil drench guidelines. A larger tree might require a commercial pesticide applicator’s assistance.
The Iowa EAB team discourages homeowners more than 15 miles from the known infestation in Alamakee County to begin preventative measures now. 2013 treatments, they say, are only appropriate if more evidence is discovered showing that EAB has moved farther into the state.
