As winter approaches, dead Scotch and Austrian Pines have been appearing with more frequency in Colorado Springs. The culprit has been found to be the Pinewood nematode, a native to North America. It does not generally cause mortality in native Pines, but in exotic Pines it causes a fatal wilt disease. It can be deadly to the Scotch, Austrian and Mugo Pines planted in our landscapes.
The Pine wilt nematode is transmitted by Pine sawyers or long horned beetles, a group of native wood borers. Infection of Pines by the nematode starts in June or July, but symptoms don’t usually appear until late summer. The tree wilts and browns quickly due to the inability of the vascular system to take up water. Dead needles often stay attached to the tree through the winter. On Scotch Pines, the entire tree usually browns quickly whereas on Austrian Pines it may be restricted to a portion of the tree. Diseased wood becomes very dry and brittle and a blue stain fungi will be present.
Removal of infected trees before May of the following year is important. If other trees nearby are at risk there are a couple inject-able compounds that are recommended for protection from the nematode.