Pine wilt is a vascular disease of pines. It is the only vascular disease of pines. It is caused by microscopic nematodes that cause the vascular system to become blocked, resulting in death of mature pines. We discussed this disease in issue no. 10 of this newsletter. If you have dead pines in your landscape, remove them now. You do not have to wait for laboratory testing. Even if the nematode is not involved, the tree is not going to recover.
The image shows two dead pines among healthy pines. The dead pines are infested with pinewood nematodes. Even if you did not know that to be fact, you can be sure that pines this far along in decline will not recover.
Why should you remove dead pines? Ultimately the goal is to protect the health of other pines within a few miles of one infested with pinewood nematodes. The beetle vector may feed on the infected tree and inadvertently pick up the nematodes, which may be transferred to a healthy pine in the feeding process. In addition, this beetle may decide to overwinter in the infested tree, become infected with nematodes, and start the whole process over in the spring. Do you need to remove roots too? No. The pinewood nematode does not invade roots. It is not a soil- or root-infecting nematode. It infests aboveground plant parts. On the other hand, entomologists tell you that some insects may decide to invade tree stumps, so make your cut flush with the soil and consider pulling the stump and/or roots. For more on pine wilt caused by the pinewood nematode, consult our online version of the Report on Plant Disease, no. 1104. It is available at http://www.ag.uiuc.edu/%7Evista/abstracts/a1104.html.