If you have fields of corn that are near or in tassel, you probably need to consider an application of fungicide against southern rust, says T.J. Binns, an agronomic service representative with Syngenta in western Kansas.
"It is a bit early for southern rust to show up, but it’s been spotted in Sumner County and in western Missouri, Georgia and Arkansas," he says. "We usually don’t see it quite this early, but the conditions have been great for rust. It likes heat and humidity and we’ve had an abundance of both."
Southern rust does not overwinter in Kansas, and it is not an annual occurrence. Kansas is infected by spores of the fungus arriving on the predominately south wind.
"When we do get it, however, it tends to be pretty widespread. It hits hard and fast," he says. "The best approach for growers is to be on the lookout for it to the south, and if it is headed your way, then treatment is a good idea."
Producers who wait until they find rust infection in their field are likely to have losses despite treating it with fungicide, simply because southern rust causes damage so rapidly. Producers whose crop is already nearing maturity won’t see as much value from applying fungicide.
Southern rust shows up as orange or red-orange pustules on the leaf. Its presence disrupts the process of photosynthesis and thereby robs the plant of being able to make the sugars it needs to fully fill the ear. If the crop has already reached milk stage, there is less benefit from applying fungicide, he says.
"You can still have losses at that stage, however," he says. "The plant will go ahead and fill that ear, but it will rob nutrients from the stalk to do it. It will put all its energy into making grain and you can wind up with a standability problem that will reduce harvest."
Binns recommends Syngenta’s Trivapro fungicide for control of southern rust. He says Trivapro is also effective against common rust in corn and stripe rust in wheat.
"It has a longer residual effectiveness than we have seen in previous products, which allows for timely application," he says. "I recommend application right at tassel for the best protection from infection up to harvest. The best practice is to apply in when you know that southern rust is present in areas to the south of you. The best results come from preventing it. Treating it after infection doesn’t produce as good of results."