For Release November 10, 1998

Pine Wilt is in the County

AGRI-VIEWS
by Chuck Otte, County Extension Agent

If you have Scots (Scotch) pine trees you need to pay real close attention! There is a disease now in the county that is 99% fatal to Scots pines. The disease is carried by an insect, treatment for either the insect or the disease is ineffective and once the tree gets the disease it will die in less than a year, often in as little as two months. That’s the bad news. The good news is that while it has occasionally been found in other species of pine trees, it has a strong preference for Scots pines and Austrian and White pines will probably be left alone (notice I said probably!)

It was just a matter of time before Pine Wilt appeared in this area. The disease was first identified in the United States in Columbia, Missouri in 1979, and shortly thereafter, also in 1979, a confirmed case was found in southeast Kansas. It has been slowly spreading east and north since then and about five years ago really started working it’s way west down I-70. It was found in Riley county last year, so I knew it was only a matter of time, and we confirmed cases in Geary County this August. One of the real problems with a disease like this is that its an nonnative disease on a nonnative tree. That always makes control a challenge!

The disease, Pine Wilt, is caused by the pinewood nematode. Nematodes are microscopic worm like organisms. The nematodes are carried into the tree by hitchhiking a ride on an insect known as the pine sawyer. Once a tree is infested, the nematodes multiply rapidly and clog up the resin canals. With these canals plugged, transpiration from the needles decreases rapidly as does the production of resin. Needles first show a gray-green discoloration then turn yellow and brown. The needles will remain attached to the trees for up to 6 to 12 months. Another important diagnostic clue is that branches become very brittle. There are other conditions that will cause needles to turn yellow or brown but in those cases the needles either fall off the tree, or the branches remain flexible and a broken branch will produce sticky resin.

The life cycle of the disease and the insect vector are very closely related. In May or June adult pine sawyers emerge from the trees. These beetles fly to new trees and feed under the bark of young pine shoots.. Here the adult beetles feed, mate and reproduce. Since the young insects feed and develop beneath the bark and within woody tissues of the trees they can be carried in logs to new locations. If the adult beetles is carrying the pinewood nematode the nematode will move into the water conducting tissue of the pine tree as the beetle feeds and makes egg laying wounds. This infestation will occur in late spring and early summer.

Once evidence of the disease becomes apparent, the tree is well on its way to death. What we normally see is the tree rapidly turning brown in August through November. If it is late summer or fall, you have a Scots Pine, it all turns brown in a hurry, the needles stay on the tree and the small branches are very brittle, you’ve got Pine Wilt.

There isn’t much that we can do to stop the disease, we can only try to reduce its spread. Dead trees need to be cut down as soon as possible. The wood from these trees would best be burned. An alternate possibility would be to chip the tree for mulch. If you chip the tree it needs to be done in the fall or early winter and then leave the mulch piled up away from any Scots pines and when it is used do not use around other Scots pines. Whichever method is used, the wood needs to be destroyed by May of the following spring. The pine sawyers seem to be attracted to stressed Scots pines so keep your trees healthy. And when you are planting new pines do not plant any more Scots pines. The disease is an unfortunate turn of events and how fast it spreads through the county will be determined by how well we clean up already infected trees! Contact the County Extension Office for more information on Pine Wilt.

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