Appling County Crop E News

Southern Corn Rust Found in Georgia. Now What?

Chris Tyson, Tattnall County Extension Agent posted the below info on his blog:

 

Southern Corn Rust Found in Georgia. Now What?

 

Southern Rust of Corn was found in Southwest Georgia last week. I wanted to share some common questions I get about it from growers in Tattnall County. I asked Dr. Bob Kemerait, Extension Corn Specialist, and these are his answers.

 

  1. I see that southern rust was found in Georgia last week.  Will a fungicide spray now still benefit me in Tattnall County even if we don’t find it our area for 2-3 weeks?  Would it be better to wait until it is closer or found in my area and then see what stage the corn is at?

 

ANSWER:  This is a great question.  I believe that very little southern rust is present in the state now and most of it is probably in the very southern part of the state.  Growers in east Georgia are most probably at lower risk than those in SW and SC Georgia.  So- there is less urgency for growers in east Georgia to spray NOW.  However, rust can move quickly and rust can EXPLODE from seemingly nothing to SOMETHING rapidly once it ignites.  Bottom line:  for growers in east Georgia, I would likely wait to spray until initial tassel or until reports of rust in the immediate vicinity warrant an earlier application.  BUT- corn growers in east Georgia with good yield potential WILL need to spray at least one fungicide application this year

 

  1. I planted my corn back in March.  It’s in the blister stage.  How long do I really need to protect my corn from southern rust?

 

ANSWER:  Another great question.  Blister stage is certainly at-risk.  Generally I feel you need to protect the crop until the hard dough stage, though some believe you need to protect until the black-layer.

 

  1. There are some really high priced fungicides out there for rust.  How do you feel about tebuconazole/Folicur compared to these other more expensive chemistries?

 

ANSWER:  Tebuconazole is a good rust material, but not so good on other diseases like northern corn leaf blight.  Additionally, it does not have the length of protective window that strobilurin and strobilurin/SDHI or strobilurin/triazole fungicides have (2 versus 3 weeks of anticipated protection).  Last season rust was especially bad in Georgia because it showed up so early.  Tebuconazole protected yield, but growers who were hard-hit were better off using better, more expensive fungicides.

 

  1.  I spayed my corn crop with a strobilurin fungicide combination two weeks ago and now you report rust.  Should I go back out and spray at 2 weeks or wait until I reach the full 3 weeks?

 

ANSWER:  I would advise waiting another week before making a second application.  As you have already sprayed and with a good product and rust pressure is in the initial stages, better to take advantage of the full spray interval and be prepared for a long fight.