Many cottonwood trees in Bismarck, particularly in Sertoma Park and nearby green spaces, are being affected by a fungal outbreak. The fungi Marssonina and Septoria are causing early browning and leaf drop, giving trees the appearance of autumn weeks ahead of schedule.
Cottonwoods are a hallmark of Bismarck’s riverfront parks, providing shade and contributing to the city’s natural landscape. The premature loss of leaves has alarmed residents who visit the park for recreation and community events.
According to local forestry experts, these fungi thrive in warm, wet summers, which matches this year’s unusual weather patterns in the Missouri River Valley. While the fungi usually don’t kill trees outright, repeated infections can weaken them and reduce long-term health, leaving them more vulnerable to other diseases and pests.
The Bismarck Forestry Division has noted that public awareness is critical. Residents are encouraged to watch for leaf spotting and report concerns to city officials to monitor spread.
I walk the park trail daily, and it looked like fall in early September. It’s unsettling to see leaves turning and dropping when summer isn’t even over,” shared Linda Kruger, a Bismarck resident.
According to North Dakota State University Extension, fungal diseases like Marssonina and Septoria are increasingly common with wetter summers. “Regular monitoring and timely cleanup of fallen leaves are the best ways to limit reinfection,” said Dr. Mark Halvorson, plant pathologist.
The early “autumn” effect may be mostly cosmetic this year, but ongoing fungal infections could affect tree vitality. The City of Bismarck Forestry Division recommends residents clear fallen leaves and avoid composting them to reduce the chance of fungal spores spreading next season.
As the city continues to monitor the situation, locals can help by reporting affected areas and staying updated through City of Bismarck Forestry alerts and NDSU Extension resources.
