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Angie Peltier

Angie Peltier
Former Extension Educator, Commercial Agriculture

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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
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Common rust in corn

Posted by Angie Peltier - Disease

Common rust of corn is caused by a fungus called Puccinia sorghi. P. sorghi and other rusts need living hosts to complete their life cycle and survive over the winter months. P. sorghi spores survive in the southern US and move northward to Midwestern corn fields along the "Puccinia pathway" (Figure). Disease can occur if weather conditions are favorable once spores land on corn plants. Cool temperatures (between 60 and 75 degrees F), high relative humidity, and wet weather favor infection. 

Common rust creates very distinct fungal fruiting structures that can help in diagnosis. Pustules are small, swollen areas of the corn leaf, created by the rust pathogen growing underneath the outer layer or epidermis of the corn leaf. When the rust pathogen produces spores, these pustules burst through the epidermis to release spores (Figure). Common rust spores are brick-red in color and can emerge from erupted pustules on either leaf surface in a scattered fashion (Figure). Spores produced in Midwestern corn fields can cause additional infections and disease in-season when weather conditions are favorable.

Common rust has been observed on lower corn leaves in many fields at the Northwestern Illinois Agricultural Research and Demonstration Center. Cool weather earlier in the growing season and more recent hot weather favored disease early and then arrested the spread of the disease later on.

Options for disease management can include both in-season and pre-season options. In-season, labeled foliar fungicides may be economical if there is considerable rust present prior to silking on susceptible hybrids and weather forecasts call for unseasonably cool and wet weather. In future growing seasons, selecting resistant hybrids and an early planting date can help to reduce the chances that disease severity will reach a high level early enough in the growing season to cause yield loss.

A good resource to help in identifying foliar diseases of corn is the online Corn Foliar Disease: Identification and Management Field Guide.

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