Archive for Thursday, January 22, 2009

Pine wilt a source of disaster for Scots

January 22, 2009

Today we continue with the second part of the two-part series on pine diseases. As I said last week, this article will emphasize pine wilt, which is the most deadly of the pine diseases. Pine wilt is very scary to those that have pines because it shows little signs of infection before the tree completely dies, there are no cures for it and there are very few good ways to prevent it. One piece of good news about pine wilt is the fact that it primarily only threatens Scots pines.

Pine wilt is caused by nematodes (microscopic roundworms) that are spread by the Pine Sawyer Beetle (a type of wood-borer). The pinewood nematode feeds and multiplies in the tree’s resin (sap) canals. This will kill the tree in just a few months. Pine wilt is common in eastern Kansas and is naturally moving westward through the state at a rate of about 10 miles per year.

The symptoms usually appear from August to December. The needles will turn grayish, green at first and then the entire tree will soon be brown and wilted. The needles and limbs will be dry compared to trees dying from other diseases. The nematodes stop the flow of resin through the tree so it is dehydrated when it finally dies.

There are not many choices in controlling this disease. Once a tree has been infested, it will likely die. There are some rather costly nematacide injections that can be administered by arborists that may provide some level of protection for unaffected trees. If you want more information about these injections, contact me or contact a certified tree care specialist for details.

If you have a tree that you suspect has pine wilt, you can cut out a 6-inch section from the interior portion of one limb (the limb needs to have at least a 2 inch diameter), bring it to the Leavenworth County Extension Office and we can send it for testing at a laboratory at K-State. It will cost you about $15 to have the test done, but the results are valuable in helping with the decision of what to do with the tree.

If your tree tests positive for pine wilt, you need to cut it down immediately to help keep the disease from spreading. If you discover your tree has pine wilt during the winter, the tree needs to be cut down before May because that is about the time the Pine Sawyer Beetles emerge and further spread pine wilt. Cut the tree off at the ground and don’t leave a stump above ground level. Do not keep the wood around for firewood. Instead, burn the wood or run it through a chipper immediately.

There are also some environmental stresses (not actual diseases) that can damage pines. Since pines aren’t native to Kansas, our weather can pose threats to them. Soil that is either too wet or too dry for long periods of time can be harmful to pines. Hot, dry winds can also hurt pines by drying out the needles and causing a brown appearance on the side of the tree facing the wind. This rarely will kill a pine but can stress it enough that it loses its vigor and becomes susceptible to diseases.

Natural needle drop is an event that occurs with some pines during the fall. This will cause the interior portions of a tree to be partially brown. It is the natural “shedding” of old needles and shouldn’t be mistaken for disease symptoms or environmental stress.

Remember that you can contact me with questions at the Leavenworth County Extension Office on the corner of Hughes and Eisenhower roads in Leavenworth, or call (913) 250-2300. I can also be reached via e-mail at mepler@ksu.edu.

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