To date no Southern Rust has been detected in corn in GA or any bordering states. Below are comments from Dr. Kemerait on the disease.
“If disease, especially southern rust, is known to be in the area, I would squeeze the trigger (apply fungicide). However, if southern rust is not found, or conditions are not favorable, I would take my finger off the trigger and wait until rust is found. No southern rust has been found; however conditions are generally favorable for development of southern rust (HOWEVER our current cool conditions will help to slow any development for a few more days..)
- Growers not at tassel can certainly wait for a fungicide application.
- Growers at tassel or silking or pollinating stages can wait to make a fungicide application until southern rust is more of a threat (that is when we find it…).
- SOME corn growers do not want to take the risk of a) the first find of southern rust being missed OR b) having to scramble to make a fungicide application and hire a plane when everyone around them wants to spray also. These farmers will often decide to spray now. I can’t disagree with their logic.
- Under current “lower risk” situation, use of a single mode of action triazole like Tilt of Domark or Tebuconazole is less expensive, generally appropriate, and will have a protective window of about 2 weeks. These fungicides are fair to good on southern rust, but less effective against northern and southern corn leaf blights.
- Under current “lower risk” situation, use of mixed products, ANY product that mixes a triazole + strobilurin, or triazole + SDHI, or SDHI + Strobilurin, or triazole + strobilurin + SDHI will provide 3 weeks of protection, better activity against rust, and better activity against corn leaf blights, but will be more expensive.
- WHEN southern rust is a clear and present threat, choice of TOP fungicides for control (Things like Trivapro, Headline AMP, Veltyma, and others) becomes prudent. More when we get to that point. “
Common Rust vs. Southern Rust
Southern rust has a much greater potential to reduce corn yields than common rust. Here’s how symptoms are different.
- Pustules of common rust are generally a) cinnamon brown in color, b) appear most frequently on lower, older leaves, and c) pustule can be found on the top and the bottom of the leaves.
- Pustules of southern corn rust are a) generally yellow-orange in color, b) appear from mid-canopy to the top of the plant, c) pustules are found on the top of the leaves only.
