At a time when the sky would appear to be the limit for Southeastern corn yields, managing diseases becomes even more important, meaning a yield difference of as many as 20 to 30 bushels per acre in some fields.
One of the biggest disease threats to corn growers — Southern rust — was practically non-existent last year due to hot, dry weather conditions, says Bob Kemerait, University of Georgia Extension plant pathologist.
“It was the first year since 2005 that I haven’t made wide-scale recommendations for spraying fungicides for high-yield producers,” says Kemerait. “It was hot and dry, and there wasn’t a way for Southern corn rust to get here — it needs a tropical storm to get to our fields.”
Southern rust, he says, is the most important disease faced by Georgia corn producers. The presence of the disease in the state is monitored in sentinel plots, he adds.
“We looked for it every week of the season but didn’t find it,” says Kemerait. “The most important aspect of the disease is that once it has sucked the juice from the leaf, it’ll start to suck it out of the stalk. When you invest in a fungicide to prevent Southern rust, you’re protecting against lodging late in the season.”
Severe Southern rust outbreaks, which typically occur every three to four years, have been linked with up to a 50-percent reduction in anticipated corn yields, says Austin Hagan, Auburn University Extension plant pathologist.
“Crop growth stage greatly impacts disease effect on yield and the need for protective fungicides,” says Hagan. “If rust shows up in corn in the tassel stage or silking, sizable yield losses are likely given favorable weather for disease development and lack of protective fungicide treatments. Double-crop corn is a sitting duck for Southern rust.”
The best way to manage Southern rust, says Kemerait is to be out in the field looking for it, or have someone else look for it. “The problem is we have two rust diseases — Southern rust, which matters, and common rust, which doesn’t matter. The best way to tell them apart in a field, if you’re scouting, or if you have someone looking for you, is that if you have orange pustules, and they are on the top and the bottom of the leaf, don’t worry about them. But if they’re only on the top of the leaf, it might be Southern rust.”
Southern rust pustules, which are distinctly orange in color, are circular to oval in shape and smaller compared to common rust, says Hagan.
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