Diplodia sapinea (Diplodia) is a fungus that causes shoot blight (dead branch tips), branch death, decreased growth, top-kill, and sometimes death, especially to pine trees with needles clustered in groups of two and three such as red, Austrian, jack, ponderosa, and Scots pines. Diplodia is seldom a concern on white pine, a five-needled pine. It is common in the Lake States and was first identified as a problem in the region in the 1970s. It is not known if Diplodia is native to Minnesota.
Diplodia can be a severe problem for young red pines growing near or under older diseased pines. Research on the long-term impact of shoot blight disease on red pine saplings found that 30 percent of planted red pine saplings died from Diplodia and Sirococcus (a nearly identical disease) over 13 years when grown within roughly 130 feet of mature red pines.
Diplodia can also be an issue in plantings when infection rates are high at nurseries and symptomless, diseased seedlings are sold. Occasionally, weather patterns can make Diplodia issues much worse at nurseries. A late spring frost in 2016 followed by an extremely stormy July (including a mega-rain event) promoted so much infection that both Minnesota and Wisconsin DNRs had to destroy hundreds of thousands of seedlings. We survey annually for Diplodia in our State Forest Nursery, and since 2016, surveys have found less than 1 percent of our seedlings with Diplodia infection, well under our 10% threshold for sale.
Location
Diplodia is widespread across Minnesota. In 2005, DNR surveys found Diplodia in 97 percent of 92 red pine stands and in all 28 jack pine stands surveyed from Morrison County north to Lake of the Woods County and east to St. Louis County.