Southern Corn Rust a Potential Problem on Local Farms.

Published 2:05 pm Tuesday, July 29, 2014

Southern Corn Rust has been found on several eastern North Carolina farming locations.

The symptoms of southern rust are orange to brown masses of spores that erupt through the upper leaf surface. Leaves, stalks, and the husks on ears may be infected. Southern rust typically sporulates profusely on the upper leaf surface and only sparsely on the lower leaf surface. In contrast, common rust produces spores on both surfaces, often in streaks.

“Southern Corn Rust has been found in both Craven and Pamlico Counties.  Both locations are only a few miles from the Beaufort County line.I believe it is only a matter of time before we find it in Beaufort County.  In fact, it is very likely that it is here now, given the proximity of the locations in Craven and Pamlico Counties,” said Rod Gurganus, Beaufort County Cooperative Extension Director in email advisories sent out between July 22 and 24.

Gurganus noted that Southern Corn Rust has also been found near Aurora in Beaufort County and near Columbia in Tyrrell County.

“If you have sprayed a fungicide two weeks ago or more, your protection may be starting to run out.In this scenario, if your corn is at R3, I would wait until Monday to assess the weather over the next few days to see if it is favorable for disease development.  By doing this, we may be able to get this corn to R4 without another fungicide application.

But as I said earlier, if you are at R3 or earlier, and you have not applied a fungicide previously, you are far more vulnerable to this disease.  There is still a chance for rain today and tonight, so conditions will be favorable,” said Gurganus.

Gurganus also advisted to not forget to assess the crop’s maturity level before spraying a fungicide for rust.
“If your corn is dented (R5), don’t spray.  If it is at R3 or earlier, apply a triazole or strobilurin/triazole combination fungicide.  There is no need to spray a strobilurin by itself at this point, since we know the disease is present.The tougher question is what to do if your corn is at R4 (dough stage).  This disease can completely kill a leaf in 5-10 days if conditions are good for it to develop and spread.  Corn is getting cheaper, and fungicides are not, so you are going to have to look at your situation to determine if the yield loss at this point is greater than the cost of applying the fungicide,” said Gurganus.

Gurganus also notes the option of spraying two different kinds of fungicides; strobilurins or triazoles.
“Strobilurins are good at preventing the disease, whereas the triazoles have curative properties.  Since it is likely that spores have already been blown into our corn (especially south of the river around Chocowinity and Aurora, etc), it might be smart to consider applying a triazole or a strobilurin/triazole combination product if you are going to spray.  The benefit of the combination products could be a slightly longer window of protection and broader spectrum control of other diseases that might be present in the field as well,” said Gurganus.