Peanut's sleep habit helps farmers fight disease

The peanut plant grows a thick canopy of compound leaves close to the ground. This structure provides for good nuts, but makes it hard for farmers to fight diseases that attack near the soil. The plants do something naturally that can help farmers fight these threats, says a University of Georgia researcher, and the difference can be night and day—literally.

In the field, the peanut plant spreads its growth to capture sunlight. It uses it to make sugar and grow healthy peanut pods below ground, says Tim Brennemen, a plant pathologist on the UGA Tifton Campus.

But at night, he said, the plant does the opposite. Instead of spreading out, its paired leaflets fold up, often revealing the base of the plant and the soil under it. Farmers can use this natural event to get fungicides through the plant’s canopy and to its base where soil-borne diseases attack.

After the tomato spotted wilt virus, Brennemen said, white mold is the peanut’s toughest enemy. It attacks low-lying parts of the plant and produces oxalic acid that kills the plant. It can go underground, too, and destroy developing peanut pods.

To fight disease, farmers typically spray peanuts with fungicides six to seven times a year. Two to three of these sprays are primarily to prevent or control white mold, he said. They almost exclusively do this during the day in the United States.

In Nicaragua a few years ago, Brennemen learned farmers there spray fungicides at night. They do this to fight white mold, which thrives in hot, humid weather. Farmers there knew the nighttime habits of the peanut plant and used it to their advantage.

Having toyed with the idea before, Brennemen and CAES graduate student Joao Augusto began experiments three years ago to see if nighttime spraying could benefit Georgia farmers. What they found surprised them.

The openness of the canopy at night allows more of the fungicide droplets to reach the lower parts of the plant. The fungicide lasts longer there, too, protected during the day by the open leaves, which prevent UV rays from reaching it and breaking it down.