Tuesday, December 20, 2011

Pine Wilt Disease

Pine wilt is a disease of pine (Pinus spp.) caused by the pinewood nematode. Here at Des Moines Golf and Country Club this pest affects our Scots Pines. We first notice flagging or browning of a limb and then the total lost of the tree. The pinewood nematode is native to North America and is not considered a primary pathogen of native pines, but is the cause of pine wilt in some non-native pines The pinewood nematode is transmitted to conifers by pine sawyer beetles either when the sawyer beetles feed on the bark and phloem of twigs of susceptible live trees or when the female beetles lay eggs in freshly cut timber or dying trees. Nematodes introduced during primary transmission can reproduce rapidly in the sapwood and a susceptible host can wilt and die within weeks of being infested if conditions are favorable to disease development. Pine wilt disease — Management of pine wilt disease is primarily limited to prevention. There are no cures for pine wilt disease once a susceptible tree becomes infested with the pinewood nematode. The most effective prevention strategy is to avoid planting non-native pines, such as Scotch and Austrian pine. Where these non-native pines already exist, landowners can reduce susceptibility of high-value landscape trees by watering to avoid drought stress. If they discover infestations, landowners can consider removing and chipping infested trees to limit the spread to nearby susceptible trees and possibly burning the effected wood. This winter we have noticed a lot of Scotch Pines with some flagging of some limbs. We are now out removing those limbs and chipping them. Hopefully we can slow down the transmission of the disease. Unfortunately I believe all of Scotch Pines someday will be lost to this pest. Here is a photo of a Scotch Pine in a landscape that has gone too long before being removed.
Yesterday we were out pruning trees that are showing signs of flagging. The nematode leaves an excretion in the vascular system of the tree. This excretion will act like glue and plug up the water conducting tissue. A sure sign of the disease is a "blue stain" in the portion of the tree that has the disease. Here is a nice cross cut photo showing that blue stain.