Pine Wilt Disease in Japan

Summary Pine wilt disease caused by the pine wood nematode, Bursaphe-lenchus xylophilus, is widespread throughout Japan except for the two northernmost prefectures. The disease has caused the death of millions of pine trees (Pinus densiflora, P. thunbergii and P. luchuensis) every year, and an annual loss in timber of as much as 1 million m3. The enormous increase in timber loss in the 1970s resulted in a loss of 2.4 million m3 in 1979. This increased loss might be due to a number of reasons. The nation’s economic and social development has led to drastic changes in the demand for pine timber. Consequently, attempts to control the disease were neglected, and dead trees left in the forests, resulting in an increase in the sources of infection and of vector, Monochamus alternatus, populations. Since 1975 the disease has spread to northern Japan. Outlying infection, resulting from the introduction of nematode-infected pine logs, is a common cause of disease occurrence in disease free areas. In warm areas such as Kyushu, where the disease occurred first in Japan in the early 20th century, the disease has destroyed many pine stands and, in most cases, they have been replaced with natural forests of broadleaved trees. In heavily damaged areas, conversion of pine forests to other tree species will be encouraged in order to keep the forest resources at a desirable level and to maintain the function of forests in land conservation. Efforts should continue to control the disease in pine forests at a primary stage of infestation in the northern regions, and other specified pine forests which play an important role for the public benefit in protecting coastline, preventing natural disaster and sustaining the aesthetic value.