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Testing Log Debarkers to Treat Logs Affected by EAB

The following information was taken from a press release dated March 2, 2006 from Michigan State University.

bark and outer log removed to prevent the spread of EAB
A pen is used for scale reference shows
how much of the bark and outer log are
removed by debarking.

Ash logs infested with emerald ash borer (EAB) can still be useful if properly debarked, say Michigan State University (MSU) and the USDA Forest Service researchers and wood utilization specialists.

Morbark Manufacturing, Inc. in Winn, Michigan, and Bedrock Express, Ltd. in Ortonville, Michigan, have cooperated with researchers to test debarking equipment that will thoroughly debark ash logs and ensure that they are free of EAB. EAB, as well as other wood-boring pests, can be spread by the transport of infested wood to locations far from their origin.

"We did this study to see if standard debarking equipment would be an option for using large ash trees that have value for lumber," says Deborah McCullough, MSU forest entomologist and a lead EAB researcher at MSU. "If enough bark and wood can be removed to eliminate EAB infestations, the logs can be transported safely to other areas and provide additional opportunities to utilize the wood."

The study was the result of the need to find more economical options to treat EAB-infested trees beyond grinding and burning them. Noting that EAB live only in the outer most layers of wood right beneath the bark, Forest Service specialist Al Steele and Ohio Department of Natural Resources forest industries specialist Andy Sabula theorized that a portable version of sawmill debarking equipment could remove enough EAB-infested bark from an ash log to make the remainder of the log useable.

EAB larvae feed on the ash's phloem, the layer found between the wood and rough, outer bark that transports water and nutrients within the tree. After feeding, the EAB spend the winter and spring as prepupae (non-feeding larvae) in small cells that they chew, about ½ inch into the wood or outer bark. Currently many of the EAB-infested ash trees growing in commercial and residential areas of Michigan have been chipped and some chips have been burned for electricity. However, because of the sheer numbers of dead and dying ash trees in the state, other methods of utilizing ash material has become a priority. Noel Schneeberger, US Forest Service forest health program leader, says finding ways to better utilize infested ash trees is important.

"We need to give serious attention to an array of options for using infested ash trees, beyond chipping and burning them," he says. "The debarking project shows that ash logs can be processed on-site and safely transported. Using large ash trees for lumber can be an economically sound option for many property owners. This study should help entice industry to play a significant role in addressing EAB infestations."

McCullough and USDA Forest Service entomologist Therese Poland sampled 41 ash logs that were provided by the Hudson Mills Park Association from the Huron Clinton Metroparks in southeastern Michigan. The logs ranged from 9 to 21 inches in diameter and most were heavily infested with EAB. A professional grader determined that 26 of the logs were high quality saw logs (logs meeting minimum regional standards of diameter, length, and defect). The other logs were crooked or had other defects that made them unsuitable as saw logs. After the Morbark model 640 machine debarked each log, the researchers measured the amount of bark and wood removed and checked the logs for any remaining EAB.

"There was a total of 7,750 EAB larvae in the 26 saw logs," McCullough says. "Of the 7,750 larvae that went into the debarker in the saw logs, none came out. On the reject logs, 3,211 EAB larvae went into the debarker in the logs, and 14 came out - 11 larvae were on one log, 1 was on a second log, and 2 were on a third log. The debarker removed a total of 99.8 percent of the bark from the trees, and 99.99 percent of the EAB larvae."

She noted that, regardless of log size, the debarker removed at least 1.4 inches of the bark and outer sapwood, even on crooked (reject) logs. The EAB prepupae were an average of 0.65 inches deep into the wood or 0.65 inches below the surface of the outer bark. Because the EAB do not burrow far into the wood, nearly the entire log is useable.

"The bigger the log, the thicker the bark," says McCullough. "On the large logs, most of the EAB prepupae were in the bark and very few were in the wood. On smaller logs with thin bark, most of the EAB were in the outer half-inch of the wood. We found that if the logs were more than 12 inches in diameter, virtually all the prepupae were in the thick bark." McCullough estimates that the 26 EAB-free saw logs would have a stumpage value of at least $250 and perhaps much more. This value is considerably more than if these logs were chipped and burned for electricity.

Vern Sandborn, sawmill specialist for Morbark Manufacturing, Inc., sees the demand for ash wood increasing. "Making fuel from these trees is at the low end of the utilization chain," he says. "Sawmills want to buy these logs, so there is a market. Prices for ash lumber are going up and some ash logs are valuable. Compare $100 to chip it with the $300 that a quality ash log could be worth." Sandborn says that all sawmills have debarkers, but if the ash logs can be debarked in the field, there is little no risk of starting a new EAB infestation and that's one less step that will have to be done at the mill. "Bedrock Express's plan is to put a chipper on the end of the debarker. That will enable them to create quality chips that can be used to produce paper from the small or crooked logs that wouldn't be suitable for lumber," he says.

Steele, who coordinated the debarking trial, said the debarking project was a success because it focused the talents and energy of diverse organizations and individuals on a very tangible problem. "The event particularly highlights the important role that the private sector can plan in addressing the EAB issue," he says. "In the end, economics will play a large role in how all exotic invasive tree pests are addressed."

The research is a cooperative effort among MSU, the USDA Forest Service, Morbark Manufacturing, Inc., Maumee Valley Resource Conservation and Development Council, and Bedrock Express. It is known that EAB-infested ash logs and firewood have caused infestations in ash trees in Michigan, Indiana and Ohio. Regulations are in place in Michigan banning the transportation of ash wood products, including logs, without compliance agreements with the Michigan Department of Agriculture. Indiana and Ohio have similar quarantine regulations. Emerald ash borer is an exotic pest that has killed an estimated 12 to 15 million ash trees in Michigan. It threatens more than 8 billion ash trees across North America.

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