A fungus traditionally found in tropical climates is threatening western Kentucky’s corn crops.
Southern rust is a disease caused by Puccinia polysora, a fungal pathogen. The infection is a common seasonal occurrence in major corn production areas in the United States and Canada. In regions where the climate allows for year-round corn growth (such as some areas in Mexico and Texas), southern rust is a persistent issue.
Wind currents carry southern rust from tropical areas to the southern United States during the warm summer months. The fungus is most infectious with high humidity and temperatures around 80 degrees Fahrenheit. Kentucky’s winter weather and seasonal growing patterns mean southern rust is only an issue during the summer. Signs of infection include circular pustules on the upper leaves of corn stalks. The spores may erupt as an orange color and fade to brown or black over time.
While southern rust can wreak havoc on crops if left untreated, proper diagnosis and management can largely prevent lower crop yield. Dr. Kiersten Wise is a plant pathologist with the University of Kentucky’s Cooperative Extension Service. She said growers with suspected cases of southern rust should contact their local cooperative extension office for an examination from an agriculture agent.
“I always encourage farmers not to panic,” Wise said. “There’s lots of information out there. The county agents are a really great resource to help you make informed decisions about whether or not you need to spray.”
Those informed decisions include a multitude of factors, Wise said.
“Whether or not southern rust is going to cause problems in farmers’ corn fields is going to depend on the time of year it gets here, what growth stage corn is when these infections occur and what the environment is doing,” Wise explained.
Shane Bogle is the cooperative extension agent for agriculture and natural resources in Caldwell County. Bogle said cases of southern rust are present in his county, and he said the timeline is typical for the yearly outbreaks.
“We typically confirm southern rust in Kentucky in about mid-July, so the timing of these findings is right on,” Bogle said.
Bogle said the infection is likely spreading throughout western Kentucky, and farmers need to regularly check their crops for the spores indicative of southern rust. Western Kentucky extension agents typically send crop samples with potential southern rust exposure to the Plant Disease Diagnostic Laboratory at the UK's research and education center in Princeton.
Western Kentucky counties with confirmed cases of southern rust include Ballard, Hickman, Graves, Caldwell, McLean and Daviess. A full map of infections may be found here. Growers interested in contacting their local extension agent may find contact information here.