Peanut producers who rely on the AU-Pnut disease advisory for making leafspot treatments might also use the program for managing soil-borne disease, according to several years of research conducted by University of Georgia plant pathologists.
AU-Pnut — developed to improve the timing of fungicide applications for controlling early and late leafspot in peanuts — can be linked successfully with soil-borne fungicides to help control disease such as white mold, limb rot and cylindrocladium black rot, says Bob Kemerait, University of Georgia Extension plant pathologist.
“The AU-Pnut advisory was developed about 10 years ago by Auburn University, and it's been proven to be very effective,” says Kemerait. “The advisory takes into account several factors or variables when scheduling fungicide applications, and it's based on using a chlorothalonil product.”
The advisory, he says, bases the first leafspot spray recommendation on the number of days since cracking. “It's similar to the calendar-based schedule when recommending the first spray. Then, the program is conservative on subsequent sprays. With a calendar-based schedule, we'll wait 12 to 14 days following that first application before making a second application.
“But rather than taking you out to the edge of your protective window, AU-Pnut starts counting rain events at 10 days. At 10 days following your first fungicide application, you have to begin paying attention to how many rain events occur,” says Kemerait.
The more rain events that occur, the more likely it is that peanut fields will begin to experience leafspot problems, he says. “The advisory also takes into account the five-day rain forecast. AU-Pnut takes into consideration all of these factors to determine whether or not a grower should be making fungicide applications,” he says.
The “first and foremost” benefit of using AU-Pnut, says Kemerait, is that it helps growers to know that they're putting out fungicides when they're most needed, and when they'll be most effective for managing diseases.
“If it's a dry year, and conditions aren't favorable for leafspot development, AU-Pnut actually can reduce your number of fungicide sprays. You can go from seven down to six, five or even four spray applications. In a very dry year, you might even get by with three sprays during the growing season. Growers hope that by using AU-Pnut, they can reduce the costs associated with making fungicide applications, including labor, fuel and the cost of the chemicals.”
A further benefit of using AU-Pnut, he says, is that any grower who uses such an advisory is forced to pay more attention to his fields. “When you pay more attention to your fields, you'll have a better idea of how to manage your crop and what needs to be done.”
Using the AU-Pnut advisory, he adds, doesn't guarantee that you'll make fewer fungicide applications. In a wet year, the advisory may call for more sprays than a calendar-based schedule.
Georgia researchers looked at AU-Pnut over 10 seasons in 13 trails with 45 fungicide comparisons, says Kemerait. On average, 5.5 sprays were made each season using AU-Pnut while an average of 7.1 sprays per season were made with a calendar-based schedule.
“Over 10 years, you would have reduced your fungicide sprays by more than one and a half. Over 45 trials, more than half the time, there was no difference in the amount of leafspot when AU-Pnut was used. In 21 of 45 trials, there actually was less leafspot in a calendar-based program.”
Just because more leafspot is present in a field isn't necessarily a bad thing, he says. “If there's no leafspot in a field, and you stayed on a calendar-based program, you may have sprayed too much. In Virginia, it has been estimated that in order to see a reduction in yield from leafspot, you must have about 40 percent defoliation. It shouldn't make a difference if you have more leafspot using AU-Pnut.”
In 43 of 45 trials, there was no yield difference between calendar-based and AU-Pnut-based tests, says Kemerait. “Over 10 years, we reduced our sprays by one and a half and maintained the same yields.”
Most peanut growers don't put out fungicides just to control leafspot, says Kemerait. They also want to control soil-borne diseases such as white mold, limb rot and possibly CBR.
“Our data shows that the AU-Pnut advisory can help you with soil-borne diseases. It has been proven to be effective in controlling both white mold and limb rot,” he says.
One option, he says, is to use AU-Pnut for leafspot control and then use the calendar-based program for soil-borne diseases. In other words, putting out Abound, Folicur, Moncut or Montero whenever the calendar indicates a spray is needed.
Another option, he adds, is to use AU-Pnut for both leafspot and soil-borne disease controls. This would be for applications made between 50 and 110 days after planting, he says.
In 17 of 19 trials, there was no difference in white mold control when AU-Pnut was used, says Kemerait. Folicur, Abound, Moncut and Montero were used at the same time in these trials. Results were similar with controlling limb rot, he adds.
“Leafspot and soil-borne diseases are different,” he says. “Spores, pathogens and epidemiology all are different. But there are important, critical similarities, and that's what makes AU-Pnut effective.”
The development of the peanut canopy, he says, can trigger white mold during the growing season. “As the peanut canopy develops, you get higher humidity and higher moisture within the canopy. This causes some defoliation, which provides a nutrient source for the fungus to feed upon. This usually occurs after 50 days. So, by starting your soil-borne coverage at 50 days, you're helping to take care of this.”
The development of both leafspot and white mold are greatest in warm, wet weather, notes Kemerait. The same conditions that enhance leafspot also cause white mold to be more severe, he says.
Rhizoctonia limb rot is most severe, he continues, when peanut vines are on the ground, and this also occurs later in the season, after 50 days.
“Pods and pegs are particularly susceptible to rhizoctonia limb rot, and they're coming in at 50 days or later. Even though leafspot and the soil-borne diseases are different, and even though the fungicides to control them are different, the same factors which affect leafspot also affect soil-borne diseases of peanut. That's why AU-Pnut works.”
Looking at specific soil-borne fungicides and how they might be implemented in AU-Pnut, Kemerait says Folicur has a 14-day protection window similar to chlorothalonil.
“Folicur can be used easily in AU-Pnut. You can insert Folicur in any trigger that occurs in the program between 50 and 110 days, and it will fit nicely. None of these soil-borne products are labeled to be used with AU-Pnuts because the companies can't control how the program is implemented.”
Abound, he says, has a 21-day window of protection. “It lasts longer in the field, so it's more difficult to find a fit for Abound. But it works just as well. Just as with Folicur, we can put Abound in at that first AU-Pnut trigger that occurs 50 days after planting.
“The second spray could be put out at the next trigger date after the first application, depending on when that occurs. It could occur as early as 11 days or much later. If you put out the second Abound application too early, you may need to consider making additional soil-borne applications later in the season. If your second application date triggers before 21 days after the first application, you can go ahead and put out chlorothalonil. If the trigger is after 21 days, you can come back with an Abound treatment.”
Less research has been completed with Moncut, says Kemerait, but it should work equally well. “The allocation of Moncut can be more flexible. It can be put out in two, three or four applications or even in one application. Moncut should be a good fit with AU-Pnut.”