Branch sampling study in Minnesota aims to improve detection of emerald ash borer, method's main benefit is finding low-level infestations

Wendy Lisney

ST. PAUL, Minnesota , December 12, 2011 (press release) – The Minnesota Department of Agriculture (MDA) has teamed up with five metro area cities, the University of Minnesota and the U.S. Forest Service to better detect new infestations of emerald ash borer (EAB). Over the next three years researchers will conduct a study where they collect branches from 300 trees in St. Paul, Minneapolis, Lauderdale, Falcon Heights and Roseville. The area is centered on the first confirmed find of EAB in Minnesota in May 2009, northwest of Highway 280 and University Ave. in St. Paul.

The method, known as branch sampling, will allow scientists to collect a total of 1,800 branches from the selected trees over the period of the study. The harvested branches will be examined for EAB and signs of stingless wasps that were released in the area to combat emerald ash borer.

Branch sampling is a new approach when it comes to searching for EAB. Currently, scientists do visual checks of ash trees looking for signs of the insect and use purple traps to detect emerald ash borer in counties previously thought to be free of EAB. Branch sampling provides a more sensitive measure than the visual evaluation and the purple traps, but due to the more intensive labor it is only appropriate in some situations. This new method has been found 75 percent effective at finding EAB, and will be an addition to the tools already used for EAB detection in Minnesota.

“The main benefit of branch sampling will be improving detection rates on low-level infestations,” said MDA Entomologist Mark Abrahamson. “Identifying areas where EAB is present is the first step in taking action to suppress the population growth and spread of this insect. Incorporating branch sampling into our work will allow for better overall management of action by the state and affected cities.”

The branch sampling has already found an EAB infested tree that appeared healthy in the Highway 280/Como Avenue area of St. Paul, less than one mile from the state’s original EAB find. Efforts will be made to slow the spread of EAB in this newly infested area.

The branch sampling study is being funded by a grant from the Minnesota Environment and Natural Resources Trust Fund as recommended by Legislative-Citizen Commission on Minnesota Resources (LCCMR). The grant money is also being used to conduct several other studies focused on EAB in Minnesota.

BACKGROUND: Since the first discovery of the insect in 2009, EAB has been confirmed in St. Paul, Minneapolis, Falcon Heights, Shoreview, rural Winona County, La Crescent and extreme southeastern Houston County.

A quarantine, which is in place in Hennepin, Houston, Ramsey and Winona counties, bars people from moving out of the affected county any items potentially infested with EAB. Items subject to the quarantine include firewood, live ash trees, ash limbs and branches, ash logs, and untreated ash lumber. A full description can be found online at www.mda.state.mn.us/plants/pestmanagement/eab/eabquarantine.aspx.

EAB is one of America’s most destructive tree pests. Its larvae kill ash trees by tunneling into the wood and feeding on the tree’s nutrients. Since its accidental introduction into North America, EAB has killed tens of millions of ash trees in 15 states. The metallic-green adult beetles are a half-inch long, and are active from May to September. Infestation signs include one-eighth inch, D-shaped exit holes in ash tree bark and winding tunnels under the bark. The biggest risk of spreading EAB comes from people unknowingly moving firewood or other ash products harboring larvae.

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