In the more than 20 years since the first outbreaks, we've learned more about the nematode and the pine sawyer beetle. One lesson was that pine wilt seldom attacks pines less than 8 to 10 years old, so it posed little threat to Scots pine Christmas tree plantations. Unfortunately, no new tricks have emerged to combat pine wilt in the landscape. Instead, the disease spread to Scots pine stands throughout Iowa, western Kentucky and eastern Kansas and Nebraska. By the late 1990s, the problem had become so severe in Iowa that ISU Extension specialists began to recommend against planting Scots pine as a landscape tree in Iowa - unless the owner was content with a tree that was unlikely to survive more than 15 to 20 years.
Nobody has a clear answer, but there are some educated guesses.
Scots pine is native to the moist, cool environment of Scotland. The Midwest's heat and drought are nothing like home for this import. The pinewood nematode is thought to be native to the Midwest, but it poses little threat to native conifers like white pine. In Japan, on the other hand, the pinewood nematode arrived by accident on logs from the United States and promptly devastated immense stands of native Japanese red and black pine. Like many severe disease epidemics, pine wilt involves an immigrant - whether it's a tree, like Scots pine in the Midwest, or the nematode, as in Japan.