How is controlling peanut diseases a lot like hunting wild hogs? You can do them both better at night, says University of Georgia Plant Pathologist Tim Brenneman.
“With wild hogs, sometimes you have to go in at night, about a half mile into the swamp, because that’s where they are,” says Brenneman. “With peanut disease, sometimes you have to spray them at night, and you have to go in after them because they’re down there in the canopy, and the fungi are located down in the soil under the plant, where they’re hard to get to.”
Brenneman says spraying for peanut diseases at night has been one of the more interesting research projects in which he has been involved in recent years. (For more click here).
Research began in 2007 and was continued in 2008 and 2009 (both in small plots and in large, on-farm studies) to assess the benefits and potential consequences of spraying fungicides at night for control of soilborne diseases.
Two large plot trials were conducted last year in southwest Georgia, he says, in fields with high yield potential. In one trial, the day and night sprays yielded the same. “In another field with higher disease pressure, the yield advantage was nearly 500 pounds per acre by simply moving those sprays to the morning before daylight rather than spraying after daylight,” says Brenneman.
Small plot university research also has confirmed the value of spraying at night and just before daylight, he says.
Although results were not as dramatic in 2008 as they were in 2007, results were similar in both seasons, says Brenneman. Control of white mold can be significantly improved by spraying the peanuts at night, there is no significant reduction in leaf spot control, and yields can be significantly improved with night sprays.
For management of soilborne diseases like white mold and Rhizoctonia limb rot, the crown of the plant is targeted for optimum control. Also, it is thought that by spraying fungicides directly into the crown of the plant, the fungicide residues are protected to some degree from sunlight, thus reducing photo-degradation and extending the period of efficacy.
“The results from research last year in Coffee County mirrored the previous year’s research,” he says. “We know that because the peanut leaves fold up when it is dark, thus opening the interior of the canopy, fungicides applied at such time would have better chance of reaching the crown of the plant,” he says.
“But is there a difference in the specific time of day or night that we make these fungicide applications?” asks Brenneman. “What we saw last year was a benefit when we sprayed in the morning, when the leaves were folded, right before daylight, and they were wet with a heavy dew to help relocate the fungicide.”
In the Coffee County trial, he explains, peanuts were sprayed late afternoon and late night — 10 p.m. to midnight — and early morning, before daylight. Peanuts were treated with Artisan at 32 ounces, Abound at 18 ounces and Provost at 21 ounces. It was a two-block spray program, with applications going out at 60 and 90 days.
“When we put these treatments out at night versus during the day, we had improved control, and if we put them on early in the morning, before daylight, we had even better control. People think if you spray at night, you won’t get good leaf spot control, and that’s true if you’re using a strictly chlorothalonil program. Growers must insure any fungicide or combination of fungicides applied at night has systemic activity against leaf spot diseases. Without systemic activity, applying a fungicide at night could led to a reduced level of leaf spot control,” says Brenneman.
An improvement in the control of white mold is more evident in non-irrigated plots than in irrigated plots when fungicides are applied in darkness, though there is likely to be benefit in both situations, he says.
In the final analysis, says Brenneman, it is believed that applying fungicides at night will either maintain yields and control white mold and leaf spot diseases or improve disease control and yields as compared to daytime applications. “There is believed to be little risk to the grower by applying fungicides at night, other than loss of a sound sleep,” he says.
He also reminds growers that only fungicides applied for control of soilborne diseases should be considered for application at night. Fungicides applied only for control of leaf spot diseases and rust should continue to be applied during the day.