Cercospora blight, the No. 1 disease that Louisiana soybean growers have to deal with year-in and year-out, is “a booger to manage,” says Boyd Padgett, plant pathologist at the LSU AgCenter.

“There are no silver bullets, no single management practice for dealing with this disease,” he said at the annual conference of the Mississippi Agricultural Consultants Association at Mississippi State University.

It is present in fields somewhere in the state every year, he says, “but when it shows up and the impact it has on yield can vary. Usually, environment is the limiting factor in the amount of disease you have, or if you have disease at all.”

And identification can sometimes be a challenge, Padgett notes.

“When scouting fields, it’s important to remember that everything that looks like a disease isn’t, and everything that looks like cercospora blight isn’t.

“I never thought soybean rust could look like cercospora blight, but we’ve looked at a lot of soybean rust and it can indeed resemble cercospora blight. So, be aware that you can have two different diseases with similar symptoms.”

Cercospora blight develops best in moderate temperatures, 68 to 86 degrees Fahrenheit, he says, and needs about 8 to 24 hours of leaf wetness.

“The fungus can be seedborne. It can overwinter on plant debris, so if you’re growing beans reduced or no-till or beans behind beans, this increases the risk for this disease. Cercospora can also be windblown.”