Anyone who cares about growing peanuts profitably into the future should be increasingly careful with how and which fungicides are used.
Diseases threaten peanut yields and are most effectively managed with a combination of crop rotation, planting less-susceptible varieties and judicious fungicides. And while a fungicide program adds to expense, losses to disease without an effective fungicide program will be more costly.
If you are a peanut farmer reading this column, you are likely starting a season-long fungicide program. Foliar-applied fungicides are used to protect against white mold (southern stem rot), Rhizoctonia limb rot, early and late-leaf spot diseases and peanut rust. In some areas, fungicides are used to protect against Sclerotinia blight.
Recently, I had a conversation with Adrian Morrell, a peanut and corn farmer in southwestern Georgia. He carefully described the program he has used. He was happy with the control, and it was one of the more cost-effective options. But he wondered if there was something more he should consider.
MOA spreadsheet
After looking at the choices of fungicides, rates and timing of applications, I told him that he had a stout program that really did not need any changes.I mentioned as new generic fungicides formulations appear on the market, he may have the opportunity to reduce the overall cost of the program, recognizing that care should be exercised in making such changes.
I also mentioned several fungicides that he had not included in his program but that he might consider using in the future. Rotating fungicides is a smart thing to do. His next comments caught me off-guard.
“Bob, looking at my MOA (mode of action) spreadsheet, it seems I am doing a better job of switching MOAs currently than I would be with your suggestions.You have told me in the past about the threat of fungicide resistance, and I want to avoid that. How many growers you talk to have a spread sheet to keep track of MOAs?”
He and I both laughed.
I had to admit that in 25 years at the University of Georgia, he was the first to give such attention to modes of action and FRAC codes.However, for the future of our fungicides and fungicides programs, it is important that more farmers pay attention.Overuse and improper use of our newer and most effective fungicides can easily lead to resistance and loss of efficacy.
I first left my footprints in a peanut field 31 years ago as a graduate student at the University of Florida.At the time, Florunner was the dominant variety, though GK-7 was gaining popularity. Chlorothalonil was widely used and Folicur (tebuconazole) had just come to market.It would be another year before Abound (azoxystrobin) and two more years before flutolanil (Moncut) arrived.
By the time I was introduced to growing peanuts, Benlate, a benzimidazole fungicide, was no longer used because of resistance issues.In those early days of my peanut career, triazole/DMI (FRAC group 3), strobilurin/QoI (FRAC group 11) and SDHI (FRAC group 7) fungicides offered great promise in the constant battle against diseases.
Fungicide arsenal
Now in 2025, peanut farmers have an amazing arsenal of fungicides to protect against diseases and yields that may exceed 6,000 pounds per acre.Fungicides from Syngenta, Nichino, Bayer CropScience, CORTEVA, BASF, FMC, ADAMA, Albaugh, Gowan, UPL and other companies help to protect yields and increase profitability.
Despite the increase in number of brand names available to peanut farmers today, the number of modes of action remain the same, with heavy use of the triazole, strobilurin and SDHI fungicides.The only fungicides that growers use in the peanut fields not in those classes are chlorothalonil, thiophanate methyl, mancozeb, dodine, sulfur, and perhaps, phosphites.
Since the early 1970s, fungicide resistance for management of leaf spot diseases of peanut has been documented for benomyl, azoxystrobin and tebuconazole.Resistance has been documented for Aspergillus crown rot to azoxystrobin.No new modes of fungicide action have been made available to peanut farmers since 1996, and resistance has developed in at least three different fungicide classes.
Adrian may have been the first to develop an MOA spreadsheet, but I hope he is not the last.