December 9, 2010
Discouraging news for pine tree owners has emerged under the microscopes at Kansas State University and the Kansas Department of Agriculture. Over the last few weeks, their labs have confirmed cases of pine wilt disease in 11 western Kansas counties.
The always-fatal disease first showed up in 1979 in both Missouri and eastern Kansas. Since then, scientists have identified cases from Canada to Mexico. Until now, however, western Kansas has harbored no signs of a true pine wilt invasion, said Jon Appel, State of Kansas plant pathologist.
“From the first, of course, one problem was the possibility that people in a wilt-free area might choose not to use local trees and wood. As part of that, infested nursery stock can be a risk. The apparent trigger at one of our new western sites was infested firewood, brought in from eastern Kansas,” said Megan Kennelly, plant pathologist with K-State Research and Extension and its Plant Disease Diagnostic Lab.
Pine wilt symptoms generally appear in late summer to late fall. First, needles turn an “off,” gray-green color. Then they brown, but don’t fall off. In many cases, the disease progresses so quickly that infected trees are dead within weeks. With late fall infections, however, trees may lose some sections or branches in fall, but wait to collapse the following spring.
The western Kansas counties with newly confirmed cases of the disease are Barber, Finney, Hodgeman, Meade, Osborne, Pawnee, Phillips, Rooks, Rush, Seward and Smith. The state’s “front-line” communities now include Beloit, Great Bend, Hays, Medicine Lodge and Pratt.
“We hope these findings are isolated occurrences and that appropriate sanitation will prevent any further spread,” Kennelly said.
Communities such as Hays, Great Bend, and Beloit have developed action plans for managing their pine wilt. In addition, local K-State Research and Extension agents are working with landowners and with the Kansas Forest Service and KDA to ensure the prompt destruction of infected trees.
“The only way to keep the disease from spreading is to remove each victim as soon as possible. Then, chip or burn its wood immediately,” Kennelly explained. “If you don’t, next spring a new generation of pine sawyer beetles will emerge from the dead wood. They’ll take wing and start looking for food.”
Each dead pine can host several hundred nesting pine sawyer larvae, Appel warned. In turn, each adult beetle that emerges in spring can carry tens of thousands of the nematodes that actually cause pine wilt.
“The beetles will even bore the holes that allow the pinewood nematodes to enter and shut down another tree’s circulation system over the summer,” he said.
Scouting visits to previous infestation sites have shown that if left unchecked, pine wilt can take out 80 percent of a mature Kansas windbreak in just five years.
Pine wilt has now been in the eastern third of Kansas for decades, and it’s continuing to exact a toll there. Trees more than 10 years old are most at risk.
The disease began to spread from there in the late 1990s, averaging about 10 miles per year, Kennelly said. It became increasingly common in the state’s central counties through the early 2000s. That’s when the watch intensified out west.
“We’re not sure why the disease invaded so many western Kansas counties this year,” Appel said. “Human factors may be involved, but western Kansas also was hot and dry last summer and into the fall. That kind of weather can increase pines’ risk, because pine sawyer beetles are attracted to stressed trees.”
Kennelly said pine wilt kills trees “that we’ve planted and valued having. “So far, the great majority of U.S. victims have been Scots – often the big, beautiful mature ones.”
In fact, the disease already has killed so many Scots pines in the Midwest that several central U.S. land-grant universities no longer recommend the once-popular species as a landscape or windbreak tree.
“As the disease has been moving west in Kansas, however, it’s actually been shifting from that norm,” Appel said. “In some of our western counties, the evergreens we’re losing are now running roughly 60 percent Scots and 40 percent Austrians. So far, we don’t know why.
“Occasionally, the disease has been attacking shrub-like mugo pines, too. Our tests have found mugos are extremely susceptible to pine wilt. The reason we don’t have more cases may simply be that Kansas doesn’t have that many mugo pines.”
Both plant pathologists hope Kansans will take serious note of the disease’s on-going spread.
“Our best control is still to destroy infected trees before the pine sawyer beetle’s life cycle can progress any further,” Kennelly said.
“But, we also need that to be a community, area and ultimately a statewide effort,” Appel added