Southern corn rust is in Georgia now, the earliest in the season the disease has appeared in the state in more than 15 years. Current weather patterns increase the risk for it to spread and growers with good yield expectations urged to take action.
University of Georgia Extension agent Andy Shirley reported the disease first last week in Mitchell County, Ga., in southeast corner of the state.
Bob Kemerait, UGA Extension plant pathologist, says, “I believe that any irrigated field corn with good yield expectations and that is at tassel or beyond is a good candidate for treating with a fungicide. Corn approaching tassel is also certainly at risk., and NOTE: do not mix an adjuvant or crop oil with the fungicide if prior to tassel stage.”
University of Georgia Extension agronomist Dewey Lee says, “Now that it is in Georgia we can expect the potential for infection to be widespread as long as the environment favors infection. Remember, southern rust spores erupt from the upper leaf side while commons erupts from both upper and lower. Southern rust spores will form on the lower surface albeit much slower than common. The spores of southern rust tend to be orange/cinnamon to brown. Southern rust is favored by temperatures in the 80’s with high humidity (or rainfall).”
Even though this southern rust infection is earlier than usual, most Georgia corn is a little ahead of schedule.
“While this might not be much comfort, it does mean we might have saved at least one spraying. Last year, it was extremely difficult to stay ahead of southern rust because the infectious time was longer than normal due to favorable conditions for infection. Some corn in the southern areas of the state is as far along as the R3/R4 stage. This makes it easier to control rust and reduce the impact since it is much closer to maturity. Much of the corn crop though, is silking to early ear development (R2/R3) which adds roughly 2 to 3 weeks of time to our potential spraying,” Lee said.
If a grower has good yield potential, and irrigated growers do, Lee recommends spraying a combination of fungicides to provide both a curative and preventative type of action.
“There are great choices today from lots of sources. You may not have a current infection taking place, but spores are active and an application of a combination of fungicides will be great insurance and likely prevent yield loss. As long as southern rust is active, I would consider staying on a 14 day spray schedule or shorter. This disease can certainly undermine all your efforts this year and significantly reduce corn yields,” Lee said.