By Blake Jackson
Southern rust of corn has been confirmed in northwestern and south-central Wisconsin, signaling that the disease is continuing its seasonal movement into northern growing regions.
Damon Smith, Extension Field Crops Pathologist in the Department of Plant Pathology at the University of Wisconsin-Madison, advises farmers to remain alert but avoid unnecessary concern.
The disease has recently been reported across southern and Midwestern states. Farmers should scout their cornfields regularly and monitor the Crop Protection Network Crop Lookout Tool for updated reports. Early detection can help producers make informed decisions about silage and grain harvest timing.
Southern rust presents its greatest yield threat when it becomes established before the R3, or milk, growth stage. Producers should identify the current growth stage of their corn and carefully inspect plants for symptoms. Southern rust is caused by the fungus Puccinia polysora.
Unlike common rust, it produces relatively small, bright orange to reddish-orange pustules that are often concentrated on the upper surfaces of leaves and appear in dense groups.
Warm conditions and high humidity encourage disease development, with temperatures near 80°F particularly favorable. The pathogen does not survive Wisconsin winters, so spores must travel north each year on wind currents from tropical areas or infected fields farther south. Consequently, previous disease history alone does not determine current risk.
Southern rust can accelerate plant drying, potentially affecting silage harvest timing and forage quality. In grain corn, growers should identify infected fields and consider prioritizing their harvest if disease progression threatens standability.
Management options include fungicide applications, particularly in areas where the disease occurs frequently. Hybrid resistance has become less dependable because resistance-breaking pathogen races have emerged.
Crop rotation and residue management generally provide little benefit because the fungus requires living corn tissue to survive.
Farmers should continue watching field conditions, weather forecasts, and disease reports throughout the season. Fungicide efficacy information and decision-support tools can help determine whether treatment is economically justified.
Growers unsure about rust identification can submit samples to the University of Wisconsin Plant Disease Diagnostic Clinic for professional diagnosis.
Photo Credit: gettyimages-dszc
Categories: Wisconsin, Crops, Corn