Bursaphelenchus xylophilus
From BugwoodWiki
Author: Megan Kennelly, Kansas State University
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Contents |
Disease Transmission
Pine wilt is caused by the pinewood nematode. The pine sawyer beetle, a long-horned borer, spreads the nematode. The nematode feeds and multiplies in the tree’s resin canals, causing wilting and death in several weeks to several months. The nematode and beetles spend the winter in the infected tree. The beetles emerge around May 1, carrying nematodes to new trees and continuing the cycle of infection.
Suseptible Hosts
Scots pines are particularly susceptible. Austrian, white, and mugo pines are also hosts, but they are not as susceptible as Scots pine.
Symptoms
Trees wilt and die in a short period of time, from several weeks to a few months. In the first stages, the needles turn grey or green, then yellow and brown. The discoloration sometimes occurs branch by branch, sometimes all at once. The brown needles stay on the tree for up to a year after the tree has died. Another key symptom is reduced resin. During part of their life, the nematodes feed on plant cells in the tree’s resin canals, stopping the flow of resin. On a healthy tree, sticky resin bleeds from the site of a wound. If a tree has pine wilt the resin is often reduced or absent, and branches become dry or brittle.
Management Strategies
1) Sanitation
The most important step is sanitation. If a tree is suspected to have pine wilt, bring a sample to your local extension office for submission to your local diagnostic dab. A branch that is at least 2 inches in diameter and 6 to 8 inches long, taken from right against the trunk, is adequate. Another option is a wedge or cross-section of trunk. If the test is positive, the tree should be cut down as soon as possible, or by May 1 at the latest, before the beetles emerge. April 1 is a better deadline to make sure no beetles emerge. Cut the tree to the ground — do not leave a stump. Chip or burn the wood immediately to destroy the beetles and nematodes. Do not save the wood for firewood.
2) Avoid stress
The beetles are attracted to drought-stressed trees. If possible, provide water during dry periods to prevent drought stress. 3) Preventative injections
There are several products available now for preventative injections. While they do not provide 100 percent control, they significantly decrease the likelihood that a tree will be infected with pine wilt. These materials provide no curative activity. Once a tree is infected there is no way to stop the disease. The materials need to be applied by a trained tree care professional. Contact your local extension office for more information.
4) Prevent new infestations
Do not import pine firewood from contaminated areas. Be wary of pine nursery stock from infested areas, and monitor nursery stock carefully. If pine wilt is introduced, remove the tree and continue to monitor surrounding pines to make sure it has not spread. Careful scouting and sanitation can eliminate sporadic outbreaks before they get out of control.
5) Avoid planting Scots Pines
Choose an alternative tree. Scots pines are highly susceptible to pine wil
Image Gallery
 Photo by L.D. Dwinell, USDA Forest Service, Bugwood.org |
 Photo by L.D. Dwinell, USDA Forest Service, Bugwood.org |
 Photo by USDA Forest Service - Rocky Mountain Region Archive, USDA Forest Service, Bugwood.org |
 Photo by USDA Forest Service - Rocky Mountain Region Archive, USDA Forest Service, Bugwood.org |
 Photo by Robert Lambe, Virginia Polytechnic Institute and State University, Bugwood.org |
 Photo by L.D. Dwinell, USDA Forest Service, Bugwood.org |
 Photo by L.D. Dwinell, USDA Forest Service, Bugwood.org |
 Photo by L.D. Dwinell, USDA Forest Service, Bugwood.org |
 Photo by USDA Forest Service - North Central Research Station Archive, USDA Forest Service, Bugwood.org |
 Photo by USDA Forest Service - North Central Research Station Archive, USDA Forest Service, Bugwood.org |
 Photo by USDA Forest Service - North Central Research Station Archive, USDA Forest Service, Bugwood.org |
 Photo by USDA Forest Service - North Central Research Station Archive, USDA Forest Service, Bugwood.org |
 Photo by USDA Forest Service - Rocky Mountain Region Archive, USDA Forest Service, Bugwood.org |
 Photo by A. Steven Munson, USDA Forest Service, Bugwood.org |
Presentation Materials
These materials may be used as long as the original author is given credit.
Pine Wilt Nematode Presentation, KSU
Importance
The importance of the pinewood nematode as a forest disease agent in the United States is unknown. It may be native to our country. In Japan, where the nematode may have been introduced, as many as 20 percent of the trees in some stands have been killed. In this country, the disease has been found more often in shade trees. The disease occurs mostly on species of pine, particularly the nonnative species. It is rare on some other species of conifers.
Identifying the Parasite
The pinewood nematode can be identified only through microscopic examination of a specimen.
Identifying the Injury
Affected trees show symptoms of wilting, coupled with a significant reduction in resin flow. Wilted trees will turn from yellow to brown within 3 months after becoming infested.
Biology
The nematode is carried from previously colonized dead pine by woodboring beetles in the genus Monochamus. The young adult beetles feed on young tissues of healthy trees and, in the process, inoculate them with nematodes.
Control
At the present time, no control for nematodes is known in the United States. In Japan, chemical control for the beetles is being tested.
References
Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html
