Word from Brian Bush, DuPont Pioneer agronomist in southern Indiana, is that southern rust has been appearing with some authority in certain counties. He has found it to be especially prevalent in west-central Indiana.
The disease normally stays to the south, with common rust sometimes appearing in the rest of Indiana, Though it's usually not a major threat, southern rust raises its head every few years when conditions favor the disease. Apparently conditions are right this year, Bush says.
Southern rust is favored by humidity and warm temperatures. Common rust prefers cool weather and humid conditions. Southern rust can be the bigger threat to grain yield, so it's important to know the difference when you find them in the field.
Southern rust appears as small, circular, pinhead shapes that are reddish orange, more reddish than common rust. The disease will also only be on the upper leaf surface. Common rust can be on both sides. Common rust will not be on ear husks, but southern rust can also infect the husks in some cases.
The real threat is to late-planted corn, Bush says. If you have late-planted fields in the southern half of the state, now would be a good time to scout them if you haven't already. It's likely too late to help earlier planted corn.
The earlier the disease comes in and the higher it is found on the plant on leaves, the greater the possibility for significant yield loss. There are several fungicides from several major companies that can control southern rust if you still have time to spray a fungicide.
If it turns very dry, the disease may stop advancing. Consider weather as a factor when deciding if you need to take action or not. The price of corn that you project you can get plus the price of application may be final factors in determining if you should spray, assuming you're still on label in that field.