Pine wilt is a serious problem on Scots, Austrian, and occasionally white pine. It is caused by the pinewood nematode and is transmitted by the pine sawyer beetle.
The symptoms for pine wilt usually appear from August through December. The trees wilt and die rapidly. The first symptoms appear three to four weeks following infestation by the pinewood nematode. Needles show a light grayish-green discoloration, and then turn yellow and brown. The needles remain attached for six months to a year after the tree has died.
Another symptom is the reduction of resin production. When branches from a healthy tree are cut, a thick, sticky resin is produced at the site of the wound. On a diseased tree, resin may be absent, so branches and twigs will become dry and break easily.
It is important to remember that rapid death is usually not the case with other pine problems, like fungal diseases, insects or environmental stress. Pines yellowed from winter burn seem similar in appearance to trees infected with pine wilt, but the branches will be flexible on the winter-damaged trees.
The pine sawyer beetles are woodborers. They emerge in May or June from infested and non-infested pine trees, and fly to new host trees, where they feed under the bark of young pine shoots. As the nematode carrying beetles feed and deposit eggs within the tree, the nematodes move to the water-conducting tissue of the pine. Their populations increase rapidly, and block the resin canals. Within four to five weeks, the nematodes will spread throughout the tree. Infested trees will die within three months. Even after the tree dies, the nematodes continue to reproduce for several months as they feed on fungi that invade the dead tree.
If you suspect that pine wilt caused the death of a tree, it is important to get confirmation so that you can act quickly to prevent the spread of the pinewood nematode to neighboring pines. In late summer or early fall, take a branch sample at least two inches in diameter, collected near the trunk of the tree, or take a wedge of wood from the lower portion of the trunk. Place the sample in a plastic bag as soon as it is collected and take it to your County Extension Office.
To control the spread of the disease, you must remove affected trees and burn the wood before May 1. To prevent the disease, keep pines stress free by controlling insects and other diseases and providing, good drainage and water during extended dry periods.