As of today (June 6), no southern corn rust has been found in Georgia or reported in neighboring states. Below are reminders from Bob Kemerait that were posted here last week.
“”Corn Growers, especially under irrigated conditions and those with good yield potential, should have their finger firmly on the fungicide trigger and begin to slowly apply pressure as tassel growth stages approaches. If disease, especially southern rust, is known to be in the area, I would squeeze the trigger. 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.”
My recommendations:
- 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. “