NPIPM:Southern rusts on corn
Authors: Byamukama, E. and Yabwalo, D.
Causal Organisms
Southern rust is caused by Puccinia polysora while common rust is caused Puccinia sorghi
Symptoms and Signs
Southern rust pustules (raised lesions full of rust spores) are light cinnamon brown to orange circular to oval and occur in clusters on the upper leaf surface. Pustules can develop on husk leaves, ear shanks, stalks and leaf sheaths. Southern rust usually develops later in the season.
Common rust pustules form on both sides of the leaf and are dark brown to cinnamon brown in color. The common rust pustules tend to puncture the leaf epidermis and can be scattered on the leaf surface. Common rust develops during the vegetative growth stages and throughout the rest of the growing season.
Disease Impacts
Sothern rust can cause severe yield loss depending on the susceptibility of the hybrid and the time of infection. Early infections especially in irrigated corn can be devastating.
Common rust tends to be less severe because of good inherent resistance in most corn hybrids. For common rust yield loss is estimated at 3-8% for each 10% increase of total leaf area infected.
Life Cycle and Epidemiology
Southern rust and common rust pathogens do not overwinter in the Midwest Region but spores are blown from southern warmer states northwards. Southern rust develops under warm humid conditions, the reason it develops later in the growing season in the Midwest. Common rust requires moderately warm temperatures (61-77 F) and high relative humidity (<95%) therefore rainy weather conditions favor common rust development.
Management Approaches
• Select resistant hybrids
• Scout and apply a fungicide if disease pressure is significant to warrant fungicide application
Other Online Resources
Crop Protection Network. Southern rust of corn. https://cropprotectionnetwork.org/encyclopedia/corn-disease-management/foliar-diseases/southern-rust/
Crop Protection Network. Common rust of corn. https://cropprotectionnetwork.org/encyclopedia/corn-disease-management/foliar-diseases/common-rust/
