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Nighttime could be right time for fungicide

The nighttime is the right time … for spraying peanuts? Short peanut rotations are putting a cap on yields in many peanut fields, but research being conducted by University of Georgia plant pathologist Tim Brenneman has shown that nighttime applications of white mold fungicides — either two or four applications, depending on the fungicide program — have helped to boost yields by more than 1,000 pounds per acre in fields with poor rotations or heavy soilborne diseases.

“The big difference is spray penetration,” says Brenneman. “The peanut canopy later in the season is often very dense with the leaves interlocking. It is very difficult for fungicides to penetrate the canopy and get to the soil where they're needed to control soilborne diseases like white mold.

“If we look at those same canopies at night, the leaves are folded through the canopy, and the fungicide penetrates to the soil where it is needed to control white mold.”

This marks the second full year of research into nighttime spraying in Georgia, he says. “We thought about it a number of years ago, but disease pressure was light at the time and the results were inconclusive.

“Then, we were traveling in Nicaragua and some of the growers there were spraying Folicur at night, in a tropical environment with a lot of heat units and humidity. The growers there said the nighttime sprays allowed the fungicide to go down through the canopy and into the soil.”

This past year was a good one for heavy white mold pressure, says Brenneman. In trials conducted in 2007, the difference in spraying during the day and at night literally was the difference between night and day, he adds. “The results were phenomenal. We sprayed Folicur and Abound, using the same sprayers, the same timing, and the same formulations, so there was no difference in input costs.”

This year, in addition to the university trials, there are grower trials in about six locations, he says. The nighttime sprays should be those in a growers' block program that specifically are for soilborne diseases, either two or four applications depending on the individual program.

Brenneman has sprayed the fungicides in his trials at 5:30 a.m., but he feels the applications would be just as successful applied anytime at night. This year, he is comparing evening applications after the leaves have folded versus the early morning applications that he made in 2007.

“The difference in the evening is that the leaves are usually dry compared to leaves that have some dew on them in the early morning,” says Brenneman.

“So we will have a folded wet leaf in the morning compared to the evening application after dark when we'll have a folded dry leaf. I don't know if this will make a difference, but we're looking at it this year. All of the data generated last year was in the early morning hours, but I feel the big difference for success will be having the leaves folded up.”

The more trouble a grower has controlling soilborne diseases — which are usually related to poorly rotated fields — the more likely a grower is to see a response to nighttime fungicide applications, says the pathologist.

“If a grower has moderate disease pressure or is getting good disease control by spraying in the day, then the grower isn't likely to see much of a difference with nighttime spraying. But if a grower is in a situation where he is getting poor white mold control and he isn't satisfied with the results of his disease program, then getting the fungicide down through the canopy and to the soil should improve white mold control,” says Brenneman.

Night applications, he adds, should be more effective in dryland situations than in irrigated fields because irrigation or a timely rain can help move fungicides down into the soil to improve white mold control. It is a common practice, he says, to irrigate to move a fungicide into the soil.

University researchers would prefer to have several years of data for any practice before making an official recommendation, says Brenneman, but they made an exception with nighttime spraying of peanut fungicides.

“We struggled with how to approach this. Some growers had terrible problems with white mold last year, and we were looking for a way to help them. This is not something for every grower in Georgia, but based on my research last year, it might be a valuable thing to consider if you have trouble with soilborne diseases,” he says.

There also may be even more of a response in reducing underground white mold incidence with nighttime fungicide applications, he says.

A systemic fungicide to control leafspot is important when making nighttime applications to get good leafspot control when the leaves are folded up, he says. Chlorothalonil is not a systemic fungicide.

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