Description: Pine wilt typically kills Scots pine within a few weeks to a few months. The needles initially turn grayish green, then tan-colored to brown. Resin flow from the wood also ceases as the tree declines. Needles remain on the dead tree for a year or more. Scattered branches on a tree may be affected initially, but the problem soon spreads to the remaining branches. In other situations, however, the entire tree turns brown all at once.

Other pine species are occasionally killed by pine wilt, and display a similar pattern of symptoms. The disease appears occasionally in Austrian (Pinus nigra), jack (P. banksiana), mugo (P. mugo), and red (P. resinosa) pines, and rarely in white pine (P. strobus). In the Midwest, however, more than 90 percent of the trees killed by pine wilt have been Scots pine. Native pine species are usually not susceptible to pine wilt.

Tree age influences the risk of pine wilt. Almost all cases of the disease have appeared in trees more than 10 years old. Pine wilt has not had a major impact on Christmas tree plantations of Scots pine. However, pine wilt has appeared in Scots pine plantations in which trees older than 10 years have not been harvested, and in abandoned Scots pine plantations. Nevertheless, the primary impact of pine wilt is on Scots pine in landscape plantings and windbreaks.

The center of the pine wilt problem in the United States is in the Midwest. Iowa, Illinois, Missouri, Kentucky, eastern Kansas, and southeastern Nebraska have experienced heavy losses of Scotspine. However, neighboring states such as Indiana, Ohio, and Minnesota have reported relatively few cases of pine wilt.

The greatest losses to pine wilt have occurred in Japan. During the 20th century, the disease spread through highly susceptible Japanese black (P. thunbergiana) and Japanese red (P. densiflora) pine forests with devastating impact. Pine wilt has appeared in China within the past 20 years, and in Korea and Taiwan within the last decade.