This devastating disease is a large factor in the mass die-off of pine trees in our area. Caused by a microscope worm in the vascular system of the tree, this disease is moved from pine to pine by the Pine Sawyer Beetle, an insect that bores into the trunk and spreads the disease. Once the nematodes are inside the bark, they rapidly reproduce, clogging the vascular system of the tree causing the tree to die. Pine trees that are infected with this disease rapidly brown and become brittle. This can take as little as 3 weeks or up to 2 years for some species that are more resistant. This browning and death occur in the summer and fall. Generally, the whole tree will turn brown at once but sometimes isolated branches will brown first. The most susceptible trees to this disease are non-native pines such as Scots and Austrian pines. Stressed Ponderosa pines can also become susceptible, however.

There is no treatment for a tree once it is infected with the nematode. Dead or infected trees should be removed and chipped or burned. This will slow the spread to other pine trees. Planting pines that are highly susceptible to the nematode should also be avoided. Scots and Austrian pines are basically a waste of time and money in our area. Desirable trees should be kept free of stress since this can make them less attractive to the borers that vector the disease. Deep water during dry spells and feed them in the fall to avoid stress. Try to avoid construction around them as this can damage roots. There are no effective chemicals to combat the pine wilt nematode at this time.