Figure 1. Southern rust on a corn leaf in Washington County, NE
Interview on Diseases in Corn and Soybeans with Nathan Mueller (Nebraska Extension) and Chad Moyer (KTIC)
Over the past week, southern rust (Figures 1-4)) is being found in some corn fields in Cuming, Dodge, & Washington Counties. Southern rust does not overwinter in Nebraska and must be blown in from the south. That is why we don’t see this disease frequently in northeast Nebraska like we do with gray leaf spot which overwinters on residue. Southern rust is different than common rust (Figures 5 & 6) and with help in identifying between the two disease, watch this short video with Extension Corn Plant Pathologist Tamra Jackson-Ziems.
Currently, southern rust has a widely variable distribution within fields and across the area. I highly recommend that all fields be scouted frequently until corn fields reach the early dent stage (R5) this year. Economic thresholds to justify a fungicide application are not well developed. Texas A&M provided guidelines in 2014 on steps to making a decision to spray a fungicide for southern rust.
- Scout. Do you have southern rust?
- Is >3% of the corn leaf area infected on at least 50% of the plants in the field?
- Did this infection occur on plants prior to the the dent stage (R5)?
If the answer is yes to these three questions, you have a higher probability of seeing a benefit from a fungicide application. However, these recommendations were developed in Texas, not Nebraska, and must be taken with some caution. Most corn is in the late blister (R2) to dough stage (R4), therefore we are not at the point of walking away from this foliar disease based on experience from extension educators in south-central Nebraska that have experienced this disease more often. Fungicides with mixed modes are action are recommended that have very good to excellent ratings for control of southern rust and other disease in the field this year including northern corn leaf blight and gray leaf spot. Products such as Headline AMP, Stratego YLD, and Quilt Xcel all fall under these recommendations for use. Please stop by your local extension office to purchase ($15) a paper copy of the 2015 Guide for Weed Management in Nebraska with Insecticide and Fungicide Information or purchase the full digital version.
To learn more about southern rust, please click on the links below:
Confirmed Southern Rust Distribution Map
UNL Corn Fungicide Trials
Fungicide Efficacy for Control of Corn Diseases Table
Corn Disease Update: Southern Rust Confirmed in Northeast Nebraska and Gray Leaf Spot Increasing
Figure 2. Topside of a corn leaf with southern rust
Figure 3. Underside of a corn leaf with southern rust
Figure 4. Southern rust of corn
Figure 5. Common rust of corn
Figure 6. Common rust of corn
