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Prevent pine wilt's spread by removing dead treesNebraska Since entering Nebraska nearly 10 years ago, pine wilt has killed an estimated 7,000 pines across the state, a Nebraska Forest Service forest health expert said. Trees infected with pine wilt die from the disease, so it is important to take steps to prevent its spread, said Mark Harrell, forest health program leader with the Nebraska Forest Service. "A chemical treatment to protect healthy pines is available, but its cost will likely limit its use to very valuable trees," Harrell said. "The only approach we have for dealing with pine wilt in most of our trees is to reduce its spread by quickly removing and destroying the trees that die from it." Pine wilt is caused by a microscopic, worm-like organism called the pinewood nematode. These nematodes live in pines and are carried from tree to tree by insects called pine sawyer beetles. Once inside the tree, the nematode disrupts the flow of sap, causing the tree to turn brown and die. Harrell said the pine sawyer beetle is active from May through September, so if trees dying of pine wilt are discovered during the fall and winter, the deadline for safely removing and destroying them is the end of April. Trees that die while the beetle is active should be removed within a month of the tree's death to prevent the beetles from re-emerging and spreading the disease to new trees. Once removed, trees should be disposed of by chipping, burning or burying to ensure beetles in the wood are killed. Chipped trees can safely be used as mulch in gardens or around trees, even pines. Because mulch resting against a tree's trunk can trap moisture and lead to decay and diseases, mulch should be kept several inches away from the trunk. Additionally, Harrell says research shows a slight risk of pine wilt spreading through infected mulch that comes in contact with trunk wounds on Scotch pine. Keeping the mulch away from the tree's trunk can help prevent this. Approximately 95 percent of the pines killed are Scotch pines, but Austrian pines occasionally are killed from the disease as well. While trees stressed by drought are slightly more susceptible to pine wilt, it easily can kill healthy trees, Harrell said. Pine wilt is very common in southeast Nebraska and is spreading to the west and north. The leading edge along which many trees are beginning to die extends from Grand Island in the west and West Point in the north. More information about pine wilt is available on the Nebraska Forest Service's website at www.nfs.unl.edu. The Nebraska Forest Service is a part of the Institute of Agriculture and Natural Resources at UNL. 5/5/08 Date: 4/28/08
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