BATON ROUGE, La. – Knowing what is causing yield loss in soybeans ranks right up there with how much loss is occurring, according to LSU AgCenter plant pathologist Clayton Hollier.

Determining how to cut those losses is part of a study Hollier is conducting that is being funded by the Louisiana Soybean and Grain Research and Promotion Board.

He’s trying to get an accurate measurement within plots of how much yield is being affected by the whole disease spectrum, not just any particular disease.

“The reason we took that approach is because in nature you’re not going to have just one disease typically, but several, each contributing to yield loss,” he said.

Some of these diseases are so minor it will be hard to measure any yield losses, but others would be very easy to measure.

The benefits of this research will be positive for the growers who want to get the most out of their crops with a good disease management program.

“In disease management, you’re looking for the best field to plant something in; it has the best drainage, easy access and good fertility, Hollier said. “And when you choose a variety, you’re looking for the most resistance against disease.”

The problem, Hollier said, is with some of the major diseases, the available varieties do not have high levels of resistance.

“So as we go through the season, scout and make decisions about fungicide use, we make them on what diseases are present in the field and what are the best products that will take care of them,” he said.

Unlike a problem with insects where you deal with thresholds, plant diseases are caused by pathogens that you cannot count, so very few thresholds exist.

What has to be determined is how much loss occurs and what the grower can do to prevent most of that loss economically.

“It’s not just about disease. It’s about the bottom line,” Hollier said. “If a fungicide is used, is it going to impact disease development, and will the grower generate more income?

“Well, he’d better, and he’d better get a lot more than he paid out,” Hollier said. “We measure yield loss so that we understand how much disease impact we’re actually dealing with.”

Hollier said a grower won’t protect against all of his losses, but he’ll get much closer with the information this project is providing.

“With disease loss research and the measurement of that loss, we are better able to guide the grower to that ‘magic’ breakeven point, where they can make better decisions about disease management and prevent both yield and quality losses and make a profit,” Hollier said.

“It tells us the total impact if the grower does or does not do certain disease management practices,” he said.

Johnny Morgan