By Blake Jackson
Tar spot has been confirmed in Wisconsin for the 2026 growing season following a positive detection in Lafayette County. The fungal disease has also been identified in neighboring states, including Iowa, Missouri, Kansas, Nebraska, Indiana, Illinois, and Minnesota.
Despite the confirmation, experts emphasize there is no reason for growers to panic, as current disease levels remain low and fungicide applications are not recommended at this time.
Instead, producers should focus on scouting fields, evaluating risk, and preparing a management strategy. Farms with a history of tar spot should assume the pathogen remains in crop residue and could trigger future outbreaks if susceptible corn and favorable weather conditions are present.
One of the best tools available is the Crop Protection Network (CPN) Tar Spot Risk Tool. Rather than detecting the disease in a specific field, the tool analyzes recent weather conditions to estimate the likelihood of disease development.
The tool considers factors such as alternating wet and dry periods, prolonged nighttime leaf wetness, high humidity, moderate temperatures, and weather patterns over the previous 14 and 30 days to generate location-specific risk assessments.
At the V8 to V10 growth stages, most corn fields do not require fungicide treatment. Early infections are generally limited to lower canopy leaves and are unlikely to affect grain yield significantly.
Growers should continue scouting, especially in fields with previous tar spot issues, susceptible hybrids, or elevated risk identified by the CPN tool. Special attention should be given to the ear leaf and the leaves above it later in the season, as these contribute the most to yield.
When fungicide applications become necessary, products containing multiple modes of action, such as QoI + DMI or QoI + DMI + SDHI, provide the strongest protection while helping reduce resistance development.
In most situations, a single application between the VT and R3 growth stages offers the best return on investment. By combining regular scouting, crop history, weather forecasts, and risk tool information, growers can make timely, informed decisions and effectively manage tar spot throughout the season.
Photo Credit: gettyimages-klosfoto
Categories: Wisconsin, Crops, Corn