NEBRASKAland Magazine is dedicated to outstanding photography and informative writing with an engaging mix of articles and photos highlighting Nebraska’s outdoor activities, parklands, wildlife, history and people.
Issue link: http://mag.outdoornebraska.gov/i/831879
Dead and dying Scotch pine, Pinus sylvestris, have become common in the eastern Nebraska landscape over the past two decades. Often the death seems shockingly rapid; a tree that was otherwise healthy looking is suddenly orange and dead within a few short weeks. The cause of the demise of Scotch pine is pine wilt. Pine wilt is caused by the pinewood nematode, Bursaphelenchus xylophilus, a microscopic worm that feeds on the living cells surrounding the resin canals of pine trees. The nematodes rapidly multiply, feeding and damaging the cells, disrupting the movement of water throughout the tree. This will lead to rapid tree death, with needle color changing from a healthy green to a dusty appearance to orange in as little as a few weeks. The nematodes cannot move from tree to tree by themselves. Instead they are assisted by pine sawyer beetles, Monochamus spp. These beetles are ¾-1½ inches in length, dark brown to blackish, with long antennae. Female beetles lay eggs under the bark of pine trees, preferring stressed or dying trees. The beetle eggs hatch out and the larvae begin to feed, tunneling into the wood. After the larvae pupate, adult beetles emerge, typically from May to September, fly to new trees, and begin to feed on twigs. The nematodes will leave the beetle's breathing tubes and enter the new tree through the feeding wounds to start a new infestation. The relationship is considered mutualistic, meaning that both the beetle and the nematode benefit. The beetle gives the nematodes a ride from tree to tree, and the nematode creates a suitable habitat in which the beetles can reproduce. Scotch pines are by far the most likely tree to be killed by pine wilt. In general, native species appear to have a high resistance to damage or death caused by pinewood nematode. Introduced species don't fare as well. Species including Austrian (P. nigra), jack (P. banksiana) and mugo (P. mugo) pines, and even occasionally eastern white pine (P. strobus) have been killed by pine wilt. In order to slow the spread of pine wilt, landowners should use basic sanitation practices. Trees that die from pine wilt should be cut down and destroyed before adult beetles can emerge from them. If a tree dies between May 1 and October 1, it is important to cut and burn, chip or bury the tree immediately. Do not save this wood for firewood – beetles will continue to emerge from it through the summer and into fall, to infest new trees. Trees that die after October 1 should be removed and destroyed before May 1, when beetle could begin to emerge. ■ Pine Wilt By Julie Van Meter State Entomologist, Nebraska Department of Agriculture Presented by it bl h bit t i JUNE 2017 • NEBRASKAland 21 MARK HARRELL, NEBRASKA FOREST SERVICE ne es s b