Southern Corn Rust has been confirmed in neighboring Coffee County. So what does this mean for Corn growers? You should be scouting your fields and should consider the stage of your corn and decide if your risk and situation warrant a fungicide application. Recent wind and pop-up thunderstorms are great transportation for southern corn rust. When looking at products your choice will come down to how long do you need to protect your corn crop. More mature corn you may be able to get by with a less expensive single mode of action product. Young corn you should look at mixed modes of action; something with a triazole and strobilurin. Our UGA Plant Pathologist Dr. Bob Kemerait has a few comments to help when evaluating your corn crop:
Finding this southern corn rust in Coffee County does 3 things.
A. It tells me that the extended period of wet we had a week or so ago helped to bring on our rust, that has been much delayed this year.
B. It tells me that all corn across the southern Coastal Plain is currently at risk for infection.
C. It tells me that even though there is currently not a whole lot of rust to be found, such could change quickly with our recent passing storms and high humidity.
What would I tell growers? Please let corn growers in SE and SW districts know that rust has been found, but still at low levels and do not panic. Tell them that corn already into dough/dent stages should not need to be sprayed for rust. Tell them that corn in late milk stage is likely safe as well. Tell them that corn at early milk, pollination/silking, and tassel is likely at risk. Tell them that Tebuconazole is a “good” rust material with a protective window of about 2 weeks. Domark (tetraconazole) is also a good-single mode of action product. Tell them that mix-ed mode of action products like Aproach Prima, Headline AMP, Priaxor, Stratego YLD, and Trivapro, to name but a few, have a longer protective window (3 weeks or so) and likely broader-spectrum activity. Tell them that if they are going to spray a fungicide, sooner is better. The more disease in a field, the harder to control.
Tell them that even if they don’t spray, they may not have a problem with rust. But do they want to gamble on that? Deciding on spraying a more-expensive fungicide or a less-expensive fungicide can be tough. Two things to consider: 1) How are your yields looking? How much do you want to protect it. 2) What growth stage is your corn, the older the corn, the less risk to disease.
For growers in NE and NW districts: no urgency to spray now, but stay tuned in.