Southern corn rust (Puccinia polysora) is confirmed for the first time in Georgia in 2012 from images sent by County Agent Rome Ethredge.
Thus far the southern rust has only been found in a single field that is south of Donalsonville. The rust is active in a “hot spot” but symptomatic plants are not found widely in the field (yet).
The affected area is planted to Pioneer 1814, so it is impossible to determine from this find whether we have the “old race” (Rpp9-sensitive) or the “new race” (Rpp9-virulent).
The field was sprayed 4 weeks ago with a tank-mix of 6 fluid ounces of Headline and 4 fluid ounces of Tebuconazole (I would expect the protective window to be no more than 3 weeks); the field will be sprayed again twith 12 fluid ounces of Quilt Xcel.
1.) Don’t think any of us are surprised to find southern corn rust now, ESPECIALLY after the passage of Tropical Storm Beryl. (Good job Rome!). Based upon the amount of rust in the field, it is very possible that the initial spores rode the winds of Beryl.
2.) Southern rust has appeared MUCH, MUCH earlier this year than it did in 2011!
2.) Conditions are VERY favorable now, have been for the past 3 days, and will continue to be favorable for the next week for further development and spread of this disease.
3.) Growers currently at greatest risk to southern rust are those in southwestern and south-central Georgia. We continue to scout sentinel plots for further spread.
4.) Growers who should weigh the importance/need for a fungicide application in the near future are those: a) in southwest and south central Georgia; b) good yield potential, c) the crop has not reached dough stage, and d) the crop has not been treated with a fungicide within the past 3 weeks.
5.) Triazole fungicides and strobilurin fungicides all have good activity against southern corn rust; triazoles will have greater systemic activity; strobilurins a longer protective window.
Growers should also consider a stink bug application with one pint per acre of methyl parathion 4EC or the high rate of a pyrethroid if they are going to make a fungicide application.
The battle is here.
(For an in-depth look at the overall corn disease situation in Georgia, see Diseases stealing profits from high-yield corn growers).