MARQUETTE - Michigan Department of Natural Resources forest health specialists said the death of tamarack trees from beetle attacks has become a growing concern in the Upper Peninsula.
The DNR said reports of dying eastern larches - more commonly known as tamaracks - have been logged from many places in the U.P. and parts of the northern Lower Peninsula. The trees are dying after continued attacks by eastern larch beetles.
The beetles, which only attack tamaracks, first became an epidemic more than a decade ago. However, the DNR said defoliation of tamarack trees in 2001 and 2002 by another insect called the larch casebearer worked, along with repeated droughts over the past 10 years, to build-up the eastern larch beetle populations.
Barks sloughs after tamarack trees damaged by eastern larch beetles die. (Michigan Department of Natural Resources photo)
A magnified image of an eastern larch beetle. (Darren Blackford, U.S. Department of Agriculture Forest Service, Bugwood.org photo)
Beetle infestations are fueled by stressing events such as defoliation, flooding, drought, fire, old age, damage from windstorms or snow breakage.
"As tamarack stands age, they become more susceptible to bark beetles," said Robert Heyd, a DNR forest health specialist in Marquette. "Because tamarack trees are intolerant of shade, stress from competition may increase as crowns close in older stands. It is important to note that not all outbreaks have been associated with obvious stressors. Eastern larch beetles appear to be capable of attacking and killing trees when no predisposing condition or factor is apparent."
The DNR recommends prompt removal of logs and using of material larger than 4 inches in diameter to remove breeding material and help reduce infestations. Infested trees, logs and slash should be removed once evidence of an infestation is detected.
"Once the eastern larch beetle builds in an area of tamarack as evidenced by initial pockets of dead trees, continued mortality is likely," Heyd said. "Those who wish to utilize the tamarack in affected areas are encouraged to harvest their tamarack quickly if (the) eastern larch beetle is active in their stand."
At some times of the year it is more difficult than others to see evidence of the beetles at work.
Heyd said from a distance, the most obvious evidence of a current infestation is yellowing foliage that develops by late July or early August. However, often heavily infested trees will not fade before the appearance of the normal fall color change.
This makes detecting currently infested trees via aerial surveys or from a distance on the ground difficult. Heavily infested trees generally fail to leaf out the following spring, the DNR said.
Heyd said when infested tamarack are examined at close range, small entrance holes -averaging just over 1/12 inch in diameter- are the only external signs of an infestation. Under the bark, beetle galleries are etched on the surface of the wood.
In fall and winter, woodpeckers often remove some or all of the bark from infested trees when searching to feed on bark beetles. By late winter and early spring, the removal reveals beetle galleries and exposes the reddish-purple inner bark or white sapwood of the tree. Debarked trees make it easy to identify an infestation, the DNR said.
For more information on eastern larch beetles or forest health issues, visit: www.michigan.gov/foresthealth.
John Pepin can be reached at 906-228-2500, ext. 206. His email address is firstname.lastname@example.org