“The other line of defense against stem rot is the use of fungicides,” he says. “We have very good fungicides, but the problem is getting them to the target where they need to be. Infections are down on the bottom of the plant, the pods and lower stems. You can have the best fungicide in the world, but it’s of little use if you can’t get it down where it needs to be.”

One method recently developed by the University of Georgia is to spray fungicides at night when the peanut leaves are folded, and when high relative humidity reduces evaporation of spray particles, allowing them to be deposited deeper in the peanut canopy. This has resulted in greatly improved control of white mold with no additional fungicide inputs, says Brenneman.

“In the daytime, the leaves are opened, and you get that interlocking layer of foliage and canopy. It’s a very difficult crop to spray down through. At night, those leaves are folded down, and you can much more effectively spray and get your fungicide down to where it needs to be.”

Researchers also are looking at making fungicide sprays for white mold early in the season, says Brenneman.

“When you think of white mold, you normally think of the noticeable symptoms that are found below ground. What we’re realizing now is how early that fungus can begin infecting a plant. With hot conditions, the fungus infects earlier, and it’s below ground. You won’t see it at this time, but the fungicide will work better if you get it out there ahead of the disease. When disease gets started, and you’re trying to shut it down, it’s much more difficult to control.”

These fungicide applications are applied in a high volume of water and a narrow band over the young plant, about three weeks after planting, he explains. At this time, there is little foliage, and the fungicide can be concentrated on the crown of the plant and even washed down toward the roots.

These products are systemic, therefore moving into the plant and back up with the growing tissue.

Most of these sprays, says Brenneman, are also effective on leaf spot, thus allowing fewer sprays later for foliar diseases. “In limited trials, this application has dramatically improved white mold control, particularly with the hotter temperatures early in the season like we’ve been experiencing.”

Under current spray programs, growers usually don’t spray at all until 30 to 40 days after planting. “But we don’t think about white mold until about 60 days after planting. Last year, we discovered that we need to be thinking about white mold as early as 21 days after planting. We’re re-evaluating the entire schedule, and we’ll probably be changing things in the next few years.”

phollis@farmpress.com


(Additional information on peanut disease control can be found at http://southeastfarmpress.com/peanuts/disease-control-still-critical-peanut-production. To see what a disease-resistant peanut variety is worth to a grower, see http://southeastfarmpress.com/peanuts/placing-value-disease-resistant-peanut-varieties-0).