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Southern corn rust cropping up in central and eastern Kansas
Hot, humid days make the perfect environment for this tropical rust that blows into the state.
2 Min Read
SOUTHERN RUST: Kansas farmers have reported southern rust (left) in corn in four counties in the state this season. Farmers should also scout for common rust (right) on corn. Courtesy of Doug Jardine, K-State Research and Extension
Hot and humid days this summer have laid out the welcome mat for a visitor to blow in from the south, say Kansas State University plant pathologists — southern corn rust.
Rodrigo Borba Onofre, from the K-State Plant Pathology department; and Chandler Day, K-State crop diagnostician, report in the July 11 Agronomy eUpdate that southern corn rust has been found in four counties in Kansas.
Unlike tar spot or gray leaf spot, southern rust doesn’t overwinter in Kansas, but blows in annually from more tropical regions. It’s become a more prevalent problem in Southern states, the experts say. Here are five steps to diagnosing and managing for southern rust.
1. Identification. Southern rust produces orange pustules of spores mainly on the upper side of the leaf. When scouting, run a finger across the pustules and the orange spores will be visible on the hand, the experts say.
2. Timing fungicide. Onofre and Day say it’s not recommended to apply a fungicide to prevent southern rust specifically, unless the disease has been observed in the canopy. They do say, however, that if a farmer applies a foliar fungicide at tasseling (VT) or silking (R1) to control tar spot and gray leaf spot, most of those fungicides are also effective for southern rust. “Depending on the product, they will have residual activity for approximately three weeks after application,” they advise. Carefully monitor the field for any change.
3. Should I spray? Onofre and Day say farmers need to consider their hybrid’s susceptibility to southern rust, the number of plants in the field affected and the crop’s growth stage before applying a fungicide. Infection early in the season on a susceptible hybrid, combined with hot and humid conditions, can be the highest risk for yield loss, they say.
4. Which fungicide should I use? A working group of corn researchers has compiled efficacy ratings for corn fungicide management of southern rust, Fungicide Efficacy for Control of Corn Foliar Diseases.
5. Send in a sample. The K-State Plant Disease Diagnostic Lab can confirm southern rust through its free testing program in the 2024 growing season. Additional information about sending in a sample can be found at K-State Plant Pathology Lab.
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