Pine Wilt Disease
Pine wilt is caused by a plant parasitic nematode referred to as the pine wood nematode, Bursaphelenchus xylophilus. The nematode is vectored by pine sawyers of the genus Monochamus and kills the tree by feeding and reproducing in the resin canals of the branch and trunk. The pine wood nematode was first reported in the United States in 1931 but was not recognized till 1979 in Missouri on Scots pine as a pathogen. Following the discovery in Missouri, the disease was discovered in southeast Kansas the same year.
Symptoms of pine wilt begin to occur in mid summer and continue into early winter in Kansas. During feeding by the adult pine sawyer after emergence in late April and May, the nematodes leave the respiratory system of the beetle and enter the wound tissue. There the nematodes transform into adults and invade the sapwood primarily feeding on resin canals. The nematodes reproduce rapidly with each generation taking only 5-6 days to complete. In four to six weeks following feeding, the nematode is systemic through the tree and symptoms begin to develop.
At first the infected tree begins to wilt and needles turn a dull green. If conditions are hot and dry, the tree rapidly dies with needles turning brown and no resin flow. Some trees die slowly up to three months of infection if conditions are not stressful. Pine sawyers continue to emerge from infected wood through the summer months resulting in new infection of nearby trees over the summer and into the fall. Overall, symptoms include flagging of branches, wilting of needles, absence of resin in branches, and rapid death of the tree. Pines affected to some extent in the Great Plains include Scots, Austrian, Japanese Black, white pine, and loblolly pines. Scots and Japanese Black pines are considered highly susceptible to the nematode. To complete the infection cycle, the pine sawyer lays its eggs into these dead and dying nematode infested trees. Inside the tree, sawyer larvae develop and overwinter in the wood. In the spring, the sawyer larvae develop into pupae which the nematodes migrate into before the emergence of the adult sawyer. The presence of pine wood nematodes in wood does not always indicate that the tree died of pine wilt. When the pine sawyer lays its eggs in dead or dying pines, it can transmit the nematode also at that time and the nematode is considered secondary to the death of the tree.
In Kansas, Scots pine in the eastern half of Kansas has had epidemic outbreaks. The disease is gradually moving westward and encompasses much of the planted range of Scots pine in Kansas. Austrian pines have also had several reports in Kansas with the nematode and seem to be ever increasing. Today, the natural western boundary of the disease is from a line from Republic County in north central Kansas to Ellsworth County in the central region southward to Harper County in south central Kansas.
Control measures include destruction of pine wilt trees by either burying or burning the wood before emergence of nematode laden adult sawyer beetles from infested wood in the spring. Diagnosis is provided by cutting ½ inch thick disks from branch wood near the trunk and sending them to a diagnostic laboratory. If you suspect this disease, please contact your local extension office or the Kansas Department of Agriculture (785) 862-2180.
PLEASE SEE: What is the Pine Wilt Initiative on this website for more information on what is being done to limit or stop the spread of the state into the remaining areas of Kansas.
Pine Wilt Information