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By Cale Cloud
Agricultural and Natural
Southern corn rust was found here in Grady County on Thursday, June 17, while I was out scouting fields.
The first case of southern rust was reported in Coffee County the week of June 7 and since then, we have had numerous reports from different counties throughout south Georgia confirming the presence of this disease. Southern rust is a disease caused by the fungal pathogen Puccinia polysora.
Movement of this disease is by windblown spores that travel northward with prevailing weather systems, so we will usually hear about it down in Florida before it gets to Georgia.
Southern rust is favored by high temperature (over 77 ºF) and high relative humidity, which tends to confine it to tropical and subtropical regions. It is often confused with common rust, which is another corn disease, but common rust isn’t nearly as damaging as southern rust. Southern rust can rapidly develop and spread under favorable conditions.
Southern rust spores have more of a “burnt orange” or reddish-orange color to them and are generally seen on the surface of leaves, not the underside. Common rust has more of a brown to cinnamon-brown color and spores can be seen on both sides of the leaves.
Rust can divert nutrients for fungal growth that would normally be used by the corn plant. This process can lead to yield loss during grain fill when plant resources are needed to contribute to the developing ear.
Rust pustules also rupture leaf epidermal tissue, which can interfere with the regulation of water loss by stomata on the leaf surface. Consequently, severe rust outbreaks may reduce the plant’s water use efficiency and infected plants may exhibit symptoms of mild drought stress. These effects can also contribute to the development of stalk rot and lodging.
Most of our growers I have talked to here in Grady County have already applied a fungicide to their corn, so they should hopefully be in good shape for the time being.
If not, now would be the perfect time to apply one if the corn has not yet reached the “dent” stage of growth, especially in irrigated corn with high yield potential.
There is a map that can be accessed online that shows counties in the southeastern United States with confirmed southern corn rust cases at: https://corn.ipmpipe.org/southerncornrust/
Those who have questions or concerns about this disease should contact the Grady County Extension Office at 229-377-1312.