Issue 5, May 22, 2009
Pine Wilt
If you are seeing large pines (15-20 years old) that have suddenly turned gray-green, then brown, consider the possibility of pine wilt. The disease may appear on one or two pines in groups of many trees. It may affect only solitary pines. The disease is spread by the Sawyer beetle and follows the pattern of the beetle’s feeding. Pinewood nematodes are the actual pathogen, but the only way they can get into a pine is via the Sawyer beetles.
We see pine wilt on Austrian, Scotch, Mugho, and just about any pine grown in Illinois EXCEPT white pines. If you see these symptoms on white pine, it is more likely that a root related problem is to blame. Consult issue #3 of this newsletter for more on white pine problems.
Pinewood nematodes get their name from the fact that they occur in the wood of the pine tree. This is an aboveground nematode. It is not found in the roots and will not be transmitted through roots or soil. It does not move from tree to tree by branch contact either. The insect vector is the only way for it to move.
Testing for this nematode is quick and easy for most diagnostic labs. Branch sections that are 2" in diameter, come from branches with brown needles attached, and are long enough to place in a vise are desired. Discs are cut from the branch in the lab. These discs are floated in water overnight. The extract is examined the next day with the use of microscopes that can confirm the species of nematode present.
What can you do about an infested tree? Since there is no chemical control for this disease, it is very important that infested trees be removed and burned, buried, or immediately chipped. Failure to do so means you risk further spread of the nematode in your area. For more details, consult Report on Plant Disease, #1104 (Adobe PDF), which you can access for free on line.--Nancy Pataky
Author:
Nancy Pataky