With the large amounts of precipitation coupled with triple digit heat, southern corn rust, (a tropical fungus uncommon in the U.S.), is spreading quickly throughout the state.
“The evaporation is much, much greater, with this heat— and its just pulling moisture out of the soil,” says Grady County Extension agent Don Clark. Although the rain is needed, he acknowledges the added moisture accelerates the spread of the southern rust fungus.
Southern corn rust was discovered for the first time on June 2 in nearby Seminole County. Clark confirmed several cases of corn rust in Grady County just a few days later, noting, the corn fungus spores often migrate to the United States from South America.
Clark says the fungus occurs about once or twice every 10 years in Georgia and recalls its occurrence here in 2008 and again in 2010. Thus far, about 10 percent of the field corn in Grady County has needed a fungicide spray in Grady County according to Clark, noting, “the disease has been the worst in the Northeast part of the county.”
Also reported but at more moderate levels in southwest Georgia is northern corn leaf blight.
“We can have disease low in the plant, and it not affect yield,” Clark affirms. “If the disease gets up to the ear leaf, and affects photosynthesis there, the test weight of the corn will be reduced.”
The test weight, Clark explained, is the weight per bushel. “The corn should weigh approximately 56 pounds per bushel. If the corn is damaged due to the fungus, he says, the profit will be reduced due to lower test weight.
Even though the corn affected has only been about 10 percent, he says, “It’s important that they spray it.”
As to timing of fungicide application, Clark advises: “Given the current findings of southern rust and northern corn leaf blight, I believe that all growers who are considering use of a fungicide to protect their crop should consider ‘first tassel/VT stage’ as the start point to determine if a fungicide is needed.”
He added, “I do not believe that every grower should initiate fungicide applications at first tassel, but this is certainly a stage to consider an application.”