By Angie Peltier and Ryan Miller
March 4, 2026’s Strategic Farming: Let’s Talk Crops session discussed whether foliar corn diseases are likely to threaten Minnesota yields in 2026. This webinar series runs through March and registrations are still being accepted: https://z.umn.edu/SF2026
To watch this episode visit: https://z.umn.edu/SF2026 http://z.umn.edu/StrategicFarmingRecordings.
There is a long list of leaf diseases that can negatively impact a corn crop’s yield potential. The diseases that have been of most recent concern in Minnesota include tar spot, southern rust, Northern corn leaf blight and Goss’s wilt and blight, the diseases that were of focus during this session.
Tar spot
Three things must be present for disease to occur, a virulent strain of a pathogen, a disease-susceptible hybrid and environmental conditions that favor disease development. Tar spot is a disease that has been of interest and concern since its arrival in the US in 2015 (and Minnesota in 2019) due to its capacity to cause severe yield loss. Phyllachora maydis, the fungus that causes tar spot, survives over winter in residue from previously infected crops and has continued to expand its range throughout Minnesota. At some point during the growing season, spores are released as primary inoculum from stroma (fungal structures) in corn residue. However, it is through repeated cycles of infection from spores produced on leaves in-season when both losses to yield potential and field to field spore movement can take place. We are fortunate in that in most of its geographic range in Minnesota, symptom severity has been low enough to not limit yield; southeast Minnesota has been and continues to be the one area of the state where yield has been most severely limited due to tar spot, although hot spots have also occurred near Monticello in the central part of the state. These ‘hot spots’ are likely driven by environmental conditions that are not yet completely understood.
Source : umn.edu