Peanut’s sleep habit helps farmers fight diseases

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 with the UGA College of Agricultural and Environmental Sciences in Tifton, Ga.

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.

They found that early morning before sunrise was the best time to spray. The dew on curled leaves helps the fungicide slide further down the plant.

Last year, Georgia farmers averaged 3,400 pounds of peanuts per acre. In research plots, switching to nighttime spraying typically improved yields by 200 pounds to 800 pounds per acre. In plots where white mold was a severe problem, nighttime spraying increased yields by 1,800 pounds per acre. In research plots where white mold was not a problem, switching spray times made little improvement.

“It was fascinating to me to see the level of improved control without there being any additional cost. That’s unusual,” said Brenneman, a plant pathologist for 25 years.

Most tractors have lights for night work. Satellites can now guide many tractors. Spraying at night, he said, wouldn’t cost farmers more money. The same product would be sprayed at the same rate, just at night. The only cost might be an occasional shift in sleeping habits.

All farmers shouldn’t rush to set the alarm earlier or pull an all-nighter to spray, he said. But the information will be useful for some.

A farmer who has had trouble controlling soil-borne diseases with fungicides or is looking to reduce costs by using less-expensive chemicals this year would see benefit, he said.

Georgia farmers will soon finish planting what is expected to be 500,000 acres of peanuts this year.

By Brad Haire
University of Georgia

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