Pine wilt disease is caused by tiny worms called pinewood nematodes and beetles called sawyers that work together resulting in a disease that rapidly discolors and kills pine trees.
Pine wilt disease impacts mostly non-native pines, including Austrian, Japanese black, Japanese red, and Scots pines. While native pines such as loblolly, spruce, and fir are not susceptible, some can become infected, especially if they are damaged by drought stress. However, native pines are rarely killed by the disease.
Nematodes carried by adult sawyer beetles start the infestation inside pine tree branches through spring feeding activities. After the introduction, the nematodes rapidly reproduce into tremendous numbers, eventually clogging the tree’s vascular system. This disrupts the plant’s water flow and stops branches from producing resin, a substance trees produce in response to injury. By mid-summer, needles will have turned brown and the entire tree eventually becomes brittle and dies. As the tree declines, sawyer beetle pupae inside the declining trees become infected with nematodes. After overwintering inside the tree, the pupae produce nematode infected adults in the spring that spread the disease to new trees.
The wood of infected branches must be tested to ensure pine wilt disease is the cause of tree decline. Consult a professional arborist for information on testing procedures. Trees with a confirmed pine wilt infection should be removed and destroyed with chipping, burning, or de-barking to prevent the disease from spreading to other plants. It is important to remove trees in winter or early spring before sawyers emerge and threaten the spread of the disease. Once the tree has been removed, an arborist can recommend non-susceptible trees to plant in their place. Be sure to provide new and existing pine trees with adequate water and fertilizer to help improve their vitality against potential infection.