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What's new in the Diagnostic Clinic:Pine Wilt Pine Wilt, caused by the pinewood nematode (Bursaphelenchus xylophilus), has been confirmed in two locations (Weld and Larimer Counties) in Colorado. This is most serious on Scots pine, but has been reported on Austrian and white pines. The pinewood nematode is transmitted from pine to pine by the pine sawyer bark beetle (Monochamus carolinensis). Symptoms usually appear from August through December. In general the trees wilt and die rapidly within a short period of time. Occasionally, trees may survive for more than one year. The needles turn yellow/brown and remain attached to the tree. The early stages of the disease are subtle and may vary.Three to four weeks following infestation, transpiration of the foliage decreases and resin production is reduced. Needles initially show a light grayish-green discoloration, then turn yellow/brown. The disease may progress uniformly through a tree or branch by branch, depending on the size of the tree and the environmental conditions during the growing season. The rapid death of a tree contrasts with other pine problems such as fungal diseases, insects or environmental stresses. In addition to rapid wilting and yellowing of the foliage, another important symptom is reduced resin production. When branches of a healthy tree are cut, a thick, sticky resin will be produced at the site of the wound; on a tree infected with pinewood nematode, resin may be absent. Branches and twigs become brittle and dry and will break easily. Trees that are yellow from winter burn may appear similar but will have flexible branches and good resin production. It is important to confirm the presence of the pinewood nematode if pine wilt is suspected to be the cause of a tree death. Early confirmation will allow the owner to act quickly to prevent the spread of the pinewood nematode to nearby pine trees. An adequate sample for nematode assay is either a branch sample at least two inches in diameter, collected near the trunk of the tree or a wedge of wood from the lower portion of the trunk. The best time to sample is late summer/early fall as nematode populations are generally high during this time. Adapted from http://www.oznet.ksu.edu/dp_hfrr/extensn/problems/pinewilt.htm |
