Overview

• Levels of foliar diseases, such as early leaf spot, were low in our experimental research trials during the 2024 growing season.  
• The high temperatures experienced in 2024 did not favor the development of foliar or soilborne diseases, not even in the untreated check.  
• Levels of disease severity were even lower than experienced in the 2023 growing season.  
• No Sclerotinia blight or southern blight was observed in the plots in 2024.

 

Field trials to address the management of significant peanut diseases in Oklahoma were established in 2024 at experimental research plots and a peanut grower’s field (on-farm research). Field trials were conducted during the 2024 peanut growing season to evaluate the efficacy of different fungicide programs to manage leaf spot diseases on Spanish market-type peanuts (cultivar OLé) following the calendar application and the recommendations of the Leaf Spot Advisor model (the Mesonet). We also conducted trials to evaluate the efficacy of in-furrow fungicides and biological control treatments to manage seedling diseases (Fusarium, Rhizoctonia, Pythium) and parasitic nematodes.  

---

Early Leaf Spot Control – Fungicide Products

 

Methods for Conducting Field Experiments

Two field trials were conducted at the Caddo Research Station near Fort Cobb to quantify the effect of fungicides on early leaf spot (ELS) severity (%), defoliation (%) and peanut yield (pounds per acre). In the first trial, fungicide treatments were applied following the calendar application method, where fungicide applications are conducted every 15 days, starting 60 days after planting (DAP). In the second trial, fungicide treatments were applied according to the recommendations of the Leaf Spot Advisor, a model developed in 1992 by John Damicone that guides fungicide applications based on weather data. The leaf spot advisor runs through the Mesonet website.

 

The soil was classified as a Binger fine sandy loam and was previously cropped with cotton. Approximately 100 pounds/acre of a granular fertilizer at 18-46-0 (N-P-K) + 2 lbs./A Sulfur + 1 lb./A Boron was incorporated into the soil on April 29. The herbicide Roundup Power Max (quarts per acre) was also applied on the same date. The herbicide Gramoxone (1 qt/A) + Crop Oil (1 qt/A) was also applied on the field on May 7 at crop pre-emergence. The research trials to evaluate the efficacy of chemical fungicides to manage foliar diseases were planted on May 13, while the trial to test the biological products was planted on May 14. The experimental design was a randomized complete block with four blocks separated by a 5-foot-wide fallow buffer. Each plot consisted of four 25-foot-long rows spaced 36 inches apart. Olé, a Spanish market-type cultivar susceptible to ELS, was used. Fungicides were broadcast through flat-fan nozzles (8002 VK) spaced 18 inches apart using a CO2-pressurized backpack sprayer. The sprayer was calibrated to deliver 20 gallons per acre at 40 psi.  
 
Fungicide applications at Trial 1 were conducted based on calendar-based fungicide programs on 15-day intervals beginning on July 19 and followed by applications on Aug. 5, Aug. 16, Sept. 4 and Sept. 16 (with a maximum of five sprays) (Table 1). Applications following the Leaf Spot Advisor were conducted based on the recommendations provided by the model beginning on July 9, followed by applications on July 29 and Sept. 16 (with a maximum of three sprays) (Table 2). All data were taken from the two center rows. Plots were dug and inverted on Oct. 3, windrowed for five days, and harvested with a combine equipped with a sacker. Pods were dried to 9% of moisture and cleaned before taking weights (in pounds) to calculate the yield. Results were analyzed using software R, version 4.4.2 (R Core Team, 2024), and mean comparisons were made using Tukey’s test.  

 

Summary of Field Conditions 

The total rainfall during the cropping period (May 14 to Oct. 8) totaled 1.11 inches for May, 0.61 inches for June, 2.99 inches for July, 1.01 inches for August, 0.72 inches for September and 0.03 inches for October. Minimum, average, and maximum air temperatures were as follows: 

• May 17-31: 61.9 ºF, 73.8 ºF and 85.8 ºF
• June: 71.0 ºF, 81.6 ºF and 93.0 ºF
• July: 69.0 ºF, 80.3 ºF and 92.0 ºF
• August: 69.0 ºF, 81.7 ºF and 95.0 ºF
• September: 61.0 ºF, 74.2 ºF and 88.0 ºF
• October 1-10: 57.4 ºF, 73.1 ºF and 89.6 ºF 

The rainfall totals during the 2024 growing season were above normal (30-year average) in July but below normal in May, June, August, September and October. The average monthly temperatures were above normal (30-year average) in May, June, August, September and October but below normal in July. The lack of rainfall experienced in most of the cropping period, coupled with the above normal temperatures, did not favor the development of early leaf spot (Passalora arachidicola) nor other foliar diseases at the experimental research plots. No southern blight (Agroathelia rolfsii) or Sclerotinia blight (Sclerotinia minor) were observed in the plots during the experiments.

 

Results From Experiments 1 and 2

Early leaf spot was not observed in the experimental research plots during the 2024 growing season (Table 1). Yield data (pounds/acre) from the untreated check did not statistically differ from the fungicide-treated plots (Table 1). This suggests that fungicide applications were unnecessary in the 2024 peanut growing season due to low disease pressure. Although not statistically different from the untreated check, the treatment combining Alto (first spray) and Miravis (second and fourth sprays) resulted in the highest yield (4,893.2 pounds/acre). Interestingly, the treatment combining Bravo (first spray) and Lucento (second and fourth sprays) resulted in the lowest yield (4,094.6 pounds/acre), although not statistically different from the untreated check. 

 

Similar results were observed in the spray programs using the same fungicides but following the recommendations for spray provided by the Leaf Spot Advisor. Early leaf spot was not observed in the experimental research plots during the 2024 growing season (Table 2). Yield data from the untreated check did not statistically differ from the fungicide-treated plots (Table 1). This suggests that fungicide applications were unnecessary in the 2024 peanut growing season due to low disease pressure. Although not statistically different from the untreated check, the treatments combining Lucento (second spray) followed by Bravo + Folicur (third spray) and Adastrio (second spray) followed by Bravo + Folicur (third spray) resulted in the highest yield of 4,631.9 pounds/acre, respectively (Table 2). The treatment where Miravis was applied only once (second spray) resulted in the lowest yield (4,334.2 pounds/acre), although it is not statistically different from the untreated check. 

---

Leaf Spot Control – Biological Products 

 

Methods for Conducting Field Experiments

In this trial, biological control products from Certis Biologicals were evaluated to quantify their effects on early leaf spot severity, defoliation  and peanut yield. Products were applied following two programs: a 15-day, calendar-based spray program, starting approximately 60 days after planting, and the recommendation provided by the Leaf Spot Advisor model. These products were applied using the same methods and dates previously described for fungicide trials 1 and 2. 

 

Results from the Biological Control Trial

Early leaf spot was not observed in the experimental research plots during the 2024 growing season (Table 3). Yield data from the untreated check did not statistically differ from the fungicide-treated plots (Table 1). Although not statistically different from the untreated check, the conventional treatment combining Bravo + Folicur (first and third sprays) and Lucento (second spray) resulted in the highest yield (4,639.1 pounds/acre) when compared with the biological control products. Interestingly, the treatment combining LifeGard WG (first and third sprays) and Convergence (second and fourth sprays) resulted in the lowest yield (4,116.4 pounds/acre), although not statistically different from the untreated check. Additional research is necessary to assess the effectiveness of biological control products in managing leaf spot diseases under moderate to high disease pressure in Oklahoma. During years with low disease pressure, like the 2024 growing season, differentiating product performance and providing reliable recommendations for future use is challenging. 

---

Acknowledgments

These experimental research trials were only possible due to the excellent cooperation with Bobby Weidenmaier and the Caddo Research Station staff. A special thanks to Merlin Schantz who generously provided a space on his farm to conduct an on-farm trial to evaluate the efficacy of in-furrow treatments to manage seedling diseases and nematodes. A special thanks to the Oklahoma Peanut Commission and the National Peanut Board for funding this research. FMC, BASF, Syngenta and Certis Biologicals provided additional funding.

---

¹ Timing corresponds to the spray dates of 1=July 19; 2=Aug. 5,; 3=Aug. 19; 4=Aug. 30; 5=Sept. 16. 
²  Values in a column followed by the same letter are not significant, according to Tukey test

---

¹ Timing corresponds to the spray dates of 1=July 9; 2=July 29; 3=Sept. 16. 
²  Values in a column followed by the same letter are not significant, according to Tukey test. 

---

¹ Values in a column followed by the same letter are not significant, according to Tukey test.