Pine wilt

Years of work to establish young pine trees, only to have them devastated by pine wilt has on more than one occasion caused windbreak owners to express great frustration. The devastation it has caused to our pine based windbreaks has made many a landowner pretty hesitant to consider pine plantings. In fact, the most heavily affected Scots pine species is no longer a recommended conservation tree, having been replaced with other pines we hope will withstand diseases like pine wilt.

Fall is when we often start to notice pine wilt symptoms. Needles on affected trees initially turn a dull gray-green. In most cases, the foliage on the entire tree is affected at the same time, although you can see individual branches affected first as well. Needles will progress from dull green to brown (often within a couple of weeks, though it can stretch out longer) and remain attached to the tree. Eventually, the tree dies. Scots pine is the most common host, but various white pine and even Austrian pine can also be affected.

Because pine wilt closely resembles drought stress—and with the levels of drought stress we saw this year—it may be difficult to discern between a tree that is infected with pine wilt and one that is under moisture stress. Drought stress can actually hasten infection by pine wilt (the beetles that carry the disease are attracted to stressed trees—go figure!), further confusing matters. Watering during drought stress situations may help ‘deter’ beetles carrying the disease.

If the twigs become brittle, they are likely dead. Check limbs to see if they have any green left in them by scraping back the outer bark layer. If the entire tree appears infected, pine wilt may be the culprit.

Unfortunately, trees infected with pine wilt cannot be saved. Trees suspected of having this disease should be cut at ground level and removed from the site or burned when possible to break the disease cycle. Wood should not be saved for firewood, as it will serve as a breeding ground for the pine sawyer—the insect that carries the nematode that results in death from pine wilt. Diseased trees may be chipped. Compost the chips for several months before using.

Currently, there are no chemical controls for curing pine wilt in an already infected tree. For trees not yet affected, preventative injections might be a possibility. The products Greyhound and Pinetect have both resulted in an 80 to 90 percent survival rate as opposed to 40 to 50 percent in untreated trees.

For information on pine wilt, as well as other common diseases of pine trees, check out Pine Diseases in Kansas available online at www.bookstore.ksre.ksu.edu/pubs/l722.pdf or from a Meadowlark Extension District Office.