By Blake Jackson
Wisconsin corn growers are being encouraged to stay alert for southern rust this season, even though the disease has not yet been confirmed in the state.
According to Damon Smith, Extension Field Crops Pathologist in the Department of Plant Pathology at the University of Wisconsin-Madison, reports from southern states show the disease is active and gradually moving north.
After southern rust caused significant damage in parts of Wisconsin during 2025, many producers are closely monitoring its potential return.
Smith advises farmers to remain calm while increasing field scouting efforts, stressing that early detection is the best way to make informed management decisions.
Southern rust poses the greatest threat when it infects corn before the milk (R3) growth stage. Infections that occur later in the season generally have less impact on grain yields, although they can still speed up leaf deterioration, reduce standability, and affect silage quality or harvest timing.
The disease, caused by the fungus Puccinia polysora, produces numerous small, bright orange to reddish-orange pustules that typically appear in clusters on the upper leaf surface.
Unlike common rust, which is frequently seen in Wisconsin, southern rust thrives in warm, humid conditions and requires very little moisture to spread.
Because the pathogen cannot survive Wisconsin winters, new spores must be carried north each year by wind currents. As a result, management focuses on regular scouting and monitoring disease reports rather than crop rotation or residue management.
Smith recommends evaluating several factors before applying fungicides, including crop growth stage, disease severity, hybrid susceptibility, weather conditions, and whether southern rust has been confirmed in the field. Since no cases have been reported in Wisconsin so far this season, preventive fungicide applications may not be necessary in many situations.
Farmers who suspect southern rust but are uncertain of the diagnosis are encouraged to submit leaf samples to the University of Wisconsin Plant Disease Diagnostic Clinic.
Accurate identification remains essential, as common rust is widespread in Wisconsin and rarely causes significant economic losses.
Photo Credit: gettyimages-awakr10
Categories: Wisconsin, Crops, Corn