Southern corn rust has been identified in Georgia (on June 5th) by Rome Ethredge in Seminole County. Corn was in the silking (R2) state. This is likely some of the earliest southern rust to affect our state. UGA Extension Pathologist Dr. Bob Kemerait has this update for growers:
- Weather condition for the past few days and over the next few days is predicted to have a significant chance of rain and humid conditions. These conditions are quite favorable for the development and spread of rust diseases to include southern corn rust and Asian soybean rust.
- As of today, 5 June- Asian soybean rust has been found on kudzu in Miller County and on corn in Seminole County.
- My recommendations: Corn in southern Georgia that is approaching tassel stage (or has reached) is now at some risk to southern corn rust. The risk is likely not urgent yet, but finding rust now (fairly early in the season) and coupled with the current weather conditions does increase risk.
- Grower spraying for southern corn rust: tebuconazole is effective, but combination products that include multiple modes of action (e.g. strobilurins, triazoles, SDHIs) have a broader spectrum of activity against disease AND have a longer protective window (e.g., 3 weeks versus 2 weeks.)
The picture above is corn in Thomas County that is also silking. We are very fortunate with our rain these past few weeks. During this stage (70-80 DAP) corn is still using 0.3 inches of water / day. We also need to watch for stink bugs. It is common to treat during the ear elongation / tassel state (VT) is 1 SB per 2 plants is present. Because they can hide from you, it is easiest to drive down the rows and check.
During policantion and blister statges (R1-R2), SB feed through the husk and damage individual kernels. Treat if you see 1 per plant.
Pyrethroids are fine to use when we’re seeing southern green SB. If brown SB are prevalent, use a high rate of bifenthrin to get about 75-90% control.