Study provides hope in fight against EAB
by John Reitman
All is not be lost for ash trees in the range now occupied by the invasive emerald ash borer.
According to recent studies conducted by researchers at Michigan State University, several treatments provided acceptable protection against the pest and the damage it can cause to ash trees. Likewise, as EAB devastates unprotected ash populations, its numbers eventually will decline in those areas, improving the outlook for desired (and protected) trees.
Researchers examined the results of six products applied as trunk injections and six others as soil drenches. In all, results of 30 treatments involving different timings were examined along with an untreated control plot.
The team of Michigan State entomologist Dave Smitley, Ph.D., research technician Kevin Newhouse and research assistant Terry Davis conducted the research trials from 2005 to 2008 on ash trees in an East Lansing, Mich., neighborhood.
At least three insecticides were effective at protecting the trees as trunk injection systems, while at least five others exhibited control as a soil drench, according to the research. Researchers defined acceptable protection as canopy thinning of 40 percent or less as well as larval density of 5 per square meter.
The research indicates that trunk injections of TREEage (emamectin benzoate), acetamiprid and Arborjet IMA (imidacloprid), as well as soil drench applications of Arena (clothianidin), Merit and IMA, Bayer Advanced (all imidacloprid), and Safari (dinotefuran) all exhibited canopy thinning of 30 percent or less as well as acceptable larval density.
The emerald ash borer is native to eastern Russia, northern China, Japan and Korea. It is thought to have entered North America aboard a cargo ship, and was first discovered on this continent in 2002 in the Detroit area. Since then, it has spread to Illinois, Indiana, Kentucky, Maryland, Minnesota, Missouri, New York, Ohio, Pennsylvania, Virginia, West Virginia, Wisconsin, Ontario and Quebec.
"Ash trees in the Detroit area are almost all dead now. They have been dying since 2003. After the first ash tree dies from EAB in any given city, it typically takes four to five years for most of he trees to die (for a city like Lansing). This may happen in two to three years for a smaller city."
- Dave Smitley, Ph.D., Michigan State University
Adult emerald ash borers, which grow to about a half-inch in length, lay their eggs in holes they create in the tree’s bark. After hatching, the larvae feed on the water-and nutrient-conducting tissue beneath the bark layer, disrupting the tree’s ability to move water and food through the tree’s vascular system. Symptoms of infestation include thinning of the canopy and sprouts growing from holes in the trunk that were created by the pests. Depending on the size, trees usually are dead within two to three years of infestation.
According to many researchers, the damage caused by EAB could rival or surpass that caused by American chestnut blight in the first half of the 20th century. A fungus that attacked the trees in the early 1900s nearly wiped out the country’s entire chestnut population by 1950.
History has shown that EAB can virtually wipe out ash populations in a short amount of time.
“Ash trees in the Detroit area are almost all dead now. They have been dying since 2003,” Smitley wrote via e-mail. “After the first ash tree dies from EAB in any given city, it typically takes four to five years for most of he trees to die (for a city like Lansing). This may happen in two to three years for a smaller city.”
While the results of the recent Michigan State research provide some good news for trees used in a closed-end study, what do they mean long term for ash trees in infested areas?
According to Michigan State’s Smitley, the prognosis is positive, and researchers predict it will become increasingly easier to protect target trees because the EAB’s numbers will decline as most of the ash trees die off in infested areas. But that does not mean desired target trees can go untreated.
“After all the untreated ash trees are dead, the EAB population declines to very low levels,” Smitley wrote. “But EAB will continue to infest the young trees sprouting from dead ones. Sprouts are common since the root system does not die.”
Smitley added that the condition of treated trees gradually improves each year during treatment, with some recovering from canopy thinning as severe as 60 percent or 70 percent.
“We now have excellent insecticide treatments that will protect ash trees over a long period of time. TREEage trunk injections last at least two years after one treatment, and imidacloprid basal drenches work when made each year.”
Many researchers believe there is little that can be done to stop the pest from spreading in North America. In Asia its spread is held in check by resistance built up by the native tree stock. None of the 20-some species of ash trees in North America have developed any sort of immunity to EAB, and all are at risk as the pest continues to spread. So far, researchers have found no climatological conditions that restrict its spread.
As a feral species, EAB also has no natural predators here. In 2007, the U.S. Department of Agriculture Animal and Plant Health Inspection Service approved the release of three species of stingless, parasitic wasps (Spathius agrili, Oobius agrili and Tetrastichus planipennisi) in hopes of finding a biological control. According to APHIS, five years of government research had been conducted before releasing the wasps, which prey on the ash borer’s eggs and larvae.
Several Webinars specific to managing ash trees in affected areas are available through the Web site www.emeraldashborer.info . The site, which contains background information, maps and the latest research data, is a collaborative effort of Michigan State, Ohio State and Purdue universities; the US Department of Agriculture Forest Service; Michigan Department of Agriculture; Michigan Department of Natural Resources; and USDA Animal and Plant Health Inspection Service.
