This is a serious article for “The H Word” this month. It does not reflect the exciting opportunities that go with outdoor living in the Hastings community. This article is meant to inform you of a disease that may well kill most of our Scotch pines in the area. We’ll get back to the fun aspects of living with a “green” attitude next month.
The best advice of the day might well be to tell you not to plant Scotch pines until we can control Pine Wilt Disease
Pine wilt is a disease of pine (Pinus spp.) caused by the pinewood nematode, Bursaphelenchus xylophilus. 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. In countries where the pinewood nematode has been introduced, such as Japan and China, pine wilt is an important non-native disease.
The pinewood nematode (Fig. 1) is transmitted (vectored) to conifers by pine sawyer beetles (Monochamus spp.) (Fig. 2) either when the sawyer beetles feed on the bark and phloem of twigs of susceptible live trees (primary transmission) or when the female beetles lay eggs (oviposition) in freshly cut timber or dying trees (secondary transmission). 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.
Pinewood nematodes introduced to fresh logs or dying trees during egg laying of sawyer beetles feed on fungi introduced by the sawyer and other bark beetles (Fig. 3).
The common presence of the pinewood nematode from such secondary transmission can confound the diagnosis of pine wilt disease. For example, if a dead or dying pine tree with pinewood nematode also has oviposition pits from sawyer beetles at the time of sampling, then pine wilt disease may not be the cause of mortality. The common presence of the pinewood nematode in forest products due to secondary transmission has resulted in restrictions on wood exports from North America.
History Pine wilt disease was first described in 1905 in Japan, but the pinewood nematode was not identified as the causal agent of this disease until 1971. Since the pinewood nematode was introduced into Japan, it has extensively damaged Japanese red pines (P. densiflora) and black pines (P. thunbergii). Analysis of DNA from several studies indicates that the pinewood nematode was introduced to Japan from the United States.
In the United States, the pinewood nematode was first reported in 1934 associated with fungi in timber, but it was not until 1979 that the nematode was reported to induce pine wilt disease of non-native pines in Missouri. Subsequent surveys and studies have established that the pinewood nematode is native to North America and not a threat to native forests. The pinewood nematode has been reported from the United States, Canada, and Mexico.
The pinewood nematode is a common secondary colonizer of freshly cut timber and dying conifers. In North America, pine wilt disease occurs predominately in non-native pines that include Austrian (P. nigra), Scotch (P. sylvestris), and Japanese red and black pines. Most documented cases of pine wilt by the pinewood nematode have occurred in the Midwestern United States.
Asian countries other than Japan began to report presence of the pinewood nematode in the mid- to late-1980s. Taiwan reported the pinewood nematode in Japanese black pine and luchu pine (P. luchuensis) in 1985. By 1989, China and Korea had also reported pinewood nematode in Japanese red and black pine. In 1999, Portugal reported the pinewood nematode present in declining maritime pine (P. pinaster) in the Iberian Peninsula.
Interceptions of the pinewood nematode from imported pine chips by the Finnish Plant Quarantine Service in 1984 resulted in a ban of untreated conifer chips and timber into Finland from countries where the pinewood nematode occurs. A year later the European Plant Protection Organization (EPPO) listed the pinewood nematode as a quarantine pest and recommended that Europe ban conifer products from countries that have the nematode unless the products have been kiln-dried. Several other countries soon adopted import restrictions on untreated softwood products.
Sources:
http://thehword.com/home_and_garden/sudden-death-of-scotch-pines/
http://www.na.fs.fed.us/spfo/pubs/howtos/ht_pinewilt/pinewilt.htm
