By Clint Thompson
A perfect storm is brewing for southern corn rust disease to wreak havoc on corn in the Southeast.
It has already been observed in three different counties in Florida and Georgia. In his 20 years of studying plant diseases at the University of Georgia, Extension plant pathologist Bob Kemerait said this is the earliest the disease has been found. Weather conditions are also favorable for the disease to spread and continue to worsen over the summer.
“We could not ask for more perfect conditions than what we have right now; humid, rain, storm blowing. You could not have a more perfect storm for infection to occur with southern corn rust,” Kemerait said. “That’s why I’m so concerned about what could happen. I don’t know what will happen but what could happen could be very ugly for growers if they’re not prepared for it.”
Southern corn rust was first discovered this year in Madison County, Florida on June 4; then in Decatur County, Georgia on June 5 and in Jeff Davis County, Georgia on June 6. If growers are not prepared, the disease can have a devastating impact on corn yields.
“In 2014 when we found it like this, we ended up having in my untreated plots from our trials, up to an 80-bushel an acre difference between where we treated and where we didn’t treat. In Alabama at an Auburn test, they had a 90-bushel an acre difference,” Kemerait said.
Southern corn rust infects corn leaves. The infected leaves cannot produce as many sugars through photosynthesis, which reduces yield. It can also drain the stalk of its strength, making corn plants vulnerable during high winds that could blow the stalks down.
If southern corn rust is contained to the bottom third of the plant, there’s still time for treatment. However, if the rust spreads upward, even in seemingly small amounts, it is much more difficult to manage.
There are chemical applications available if applied in a timely manner.
“All of our fungicides will work better under preventative conditions or spraying when there’s very early infection. No matter what we spray, if we’re spraying after we can walk out in a field and don’t have to hunt too hard to find rust, it’s hard to put that genie back in the bottle,” Kemerait said. “Preventative spray is by far our most effective spray.”