Integrated Management of Peanut Diseases in Oklahoma
Maira R. Duffeck, Carlos Theodoro, Luana Muller, Gabriel F. Paiva and Estefania Rodriguez, Oklahoma State University Department of Entomology and Plant Pathology
Rebecca S. Bennett and Kelly D. Chamberlin, USDA-Agricultural Research Service
Overview
- Early leaf spot was present in the trials during the entire growing season in the lower canopy and at low levels. An increase in disease severity was observed in the untreated plots at the end of the growing season in the second week of September.
- Levels of early leaf spot severity (%) in 2025 were greater than those experienced in the 2024 growing season.
- No Sclerotinia blight or Southern blight was observed in the plots in 2025.
Field trials to address the management of important peanut diseases in Oklahoma were established in 2025 at Caddo Research Station near Fort Cobb. Field trials were conducted during the 2025 peanut growing season to evaluate the efficacy of different fungicide programs to manage leaf spot diseases on Spanish market-type peanuts (cultivar OLé). Two application programs were used:
- Calendar-based: Fungicides were applied using the calendar application with sprays conducted every 15 days, starting 60 days after planting
- Leaf Spot Advisor: Fungicides were applied following the recommendations provided by the Leaf Spot Advisor model, which is available on the Mesonet webpage. The Leaf Spot Advisor is a weather-based management tool that determines when enough infection hours have occurred to cause foliar diseases, indicating that a fungicide application should be considered.
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.
Methods for Conducting Field Experiments
Two field trials were conducted at the Caddo Research Station near Fort Cobb to quantify the impact of fungicide programs on early leaf spot (ELS) severity (%), defoliation (%) and peanut yield (pounds per acre, lbs./A). In the first trial, fungicide treatments were applied following the calendar application method, where fungicide applications are conducted every 15 days, starting at 60 days after planting (DAP). In the second trial, fungicide treatments were applied according to the recommendations of the Leaf Spot Advisor, a weather-based management tool developed by John Damicone in 1992, which identifies when enough infection hours for the development of foliar diseases have occurred and a fungicide should be considered. Currently, the Leaf Spot Advisor runs through the Mesonet webpage.
Trials were conducted at a field that has a soil classified as a Binger fine sandy loam and was previously cropped with peanuts. The peanut trials were managed following a well-defined schedule of field operations. On Jan. 8, the area was fertilized with 100 lbs./A of 0-0-60 (N-P-K). Soil preparation included plowing on April 1, disking on April 9 and field cultivation on April 10. Also, on April 10, 100 lbs./A of 18-46-0 (N-P-K) plus 1 lbs./A of boron were applied and incorporated. Weed management consisted of Prowl (1 qt) applied and incorporated on May 5 and May 13. When the trials were planted, Valor (2 fluid ounces, fl oz) was applied. A post-emergence application was made on July 9 with Dual Magnum (1.3 pint) + Basagran (1 quart) + Clethodim (1 pint) + Dyne-Amic (6 fl oz). The trials were planted in a randomized complete block design with four replications, separated by 5-foot-wide fallow buffers. Each plot consisted of four 25-foot-long rows spaced 36 inches apart. The peanut cultivar Olé, a Spanish market-type variety susceptible to early leaf spot (ELS), was used in this study. Fungicides were applied as broadcast sprays through cone nozzles spaced 18 in. apart using a CO₂-pressurized backpack sprayer. The sprayer was calibrated to deliver 20 gallons per acre (gal/A) at 40 pounds per square inch (psi).
Fungicide applications based on the calendar-based program were conducted on 15-day intervals, beginning on July 16 and followed by applications on July 31, Aug. 21 and Sept. 12 with a maximum of four applications during the growing season. Applications under the Leaf Spot Advisor program were made based on the model recommendations on June 26, followed by applications on July 16 and Aug. 21, with a maximum of three applications during the growing season. Data on early leaf spot severity (%) and defoliation (%) were collected on Oct. 2 in the two center rows of each plot. The two center rows of each plot were dug and inverted on Oct. 8, windrowed for five days, and harvested with a combine equipped with a sacker. Pods were dried to 9% moisture, cleaned and weighed to determine yield (lbs./A). Data were analyzed using R software version 4.4.2 (R Core Team, 2024), and means were compared using Tukey’s test at P = 0.05.
Summary of Field Conditions
During the 2025 peanut growing season at Fort Cobb, rainfall was highly variable. May and July were particularly dry (1.1 and 0.8 in, respectively), while June, August and September received moderate rainfall (4.0-4.7 in). Average temperatures were generally warm throughout the season, with July and August experiencing the highest averages (81.2 °F and 78.4 °F, respectively). The combination of irregular rainfall and warm conditions likely created favorable conditions for early leaf spot development, which progressed to high severity by late season.
Results From the Fungicide Efficacy Trials
For the calendar-based application program, all treatments significantly reduced disease severity (%) and defoliation (%) (P < 0.05) compared with the untreated check (Table 2). The lowest disease severity and defoliation ratings were observed with programs, including Miravis alone or in combination with other products (treatments 5 and 8). However, disease severity in these treatments did not differ statistically from treatments 2, 3, 6 and 7, indicating comparable performance among these fungicide programs in reducing disease. A similar trend was observed for defoliation. Although treatments 5 and 8 resulted in the lowest numerical values, they were not statistically different from treatments 2, 3, 6 and 7, suggesting that these programs provided equivalent levels of defoliation control. Regarding peanut yield, all treatments increase yield (lbs./A) compared with the untreated check (Table 2). The highest yield values were observed with programs, including Elatus alone or in combination with other products (treatments 6 and 9). However, yield in these treatments did not differ statistically from treatments 2, 3, 4, 5, 7, 8 and 11, indicating comparable performance among these fungicide programs in protecting yield.
For the Leaf Spot Advisor application program, all treatments significantly reduced disease severity (%) and defoliation (%) (P < 0.05) compared with the untreated check (Table 3), except for treatment 10, which did not differ significantly from the untreated control. These results indicate that two applications of Umbra at 60 and 75 DAP applied at the lower rate (25 fl oz/A) do not provide sufficient residual control to protect against late-season infections that typically occur toward the end of the peanut growing season. The lowest disease severity and defoliation ratings were observed with programs, including Miravis alone or in combination with other products (treatments 5 and 8) and Lucento in combination with Bravo weather stik (treatment 7). However, disease severity in these treatments did not differ statistically from treatments 2, 3, 4, 6 and 9, indicating comparable performance among these fungicide programs in reducing disease. A similar trend was observed for defoliation. Although treatments 5, 7 and 8 resulted in the lowest numerical values, they were not statistically different from treatments 2, 3, 4 and 6, suggesting that these programs provided equivalent levels of defoliation control. The treatment with Umbra applied at the lower rate (25 fl oz/A) did not differ significantly from the untreated control and was not able to prevent peanut defoliation by the end of the growing season. Regarding peanut yield, all treatments increased yield (lbs./A) compared with the untreated check (Table 2). The highest yield values were observed with the fungicide program, including Abound in combination with Bravo weather stik and Tebuzol (treatment 4). However, yield in this treatment did not differ statistically from treatments 2, 3, 5, 6, 7, 8, 9, 10 and 11, indicating comparable performance among these fungicide programs in protecting yield.
Acknowledgements
The experimental research trials were possible due to the excellent cooperation established with the Caddo Research Station staff. A special thanks to the Oklahoma Peanut Commission and the National Peanut Board for funding to support this research. FMC, Syngenta, Nichino and Certis Biologicals provided additional funding for the trials.
Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. The USDA is an equal opportunity provider, employer and lender.
| Months | Total Rainfall in. | Maximum Temperature oF | Average Temperature oF | Minimum Temperature oF |
|---|---|---|---|---|
| May (13-31) | 1.1 | 84.3 | 72.2 | 59.5 |
| June | 4.0 | 89.0 | 78.0 | 69.0 |
| July | 0.8 | 92.0 | 81.2 | 71.0 |
| August | 4.7 | 89.0 | 78.4 | 69.0 |
| September | 3.5 | 85.0 | 72.5 | 62.0 |
| October (1-8) | 0.0 | 83.7 | 70.8 | 60.7 |
| Treatment Number | Product, Rate, Timing1 | Early Leaf Spot (%)2 - Oct. 2* | Defoliation (%)2 - Oct. 2* | Yield (lbs./A)2 |
|---|---|---|---|---|
| 1 | Untreated check | 42.88 a | 47.50 a | 4,842 c |
| 2 | Lucento 5.5 fl oz (1, 3); Bravo weather stik 24 fl oz + Tebuzol 7.2 fl oz (2) | 5.25 de | 5.38 cd | 5,481 ab |
| 3 | Adastrio 9 fl oz (1, 3); Bravo weather stik 24 fl oz + Tebuzol 7.2 fl oz (2) | 6.38 de | 8.25 cd | 5,415 abc |
| 4 | Bravo weather stik 24 fl oz + Tebuzol 7.2 fl oz (2); Abound flowable 18.5 fl oz (3, 4) | 10.75 bcd | 15.00 bcd | 5,437 abc |
| 5 | Alto 5.5 fl oz (1); Miravis fl oz/A 3.4 (2, 3) | 1.75 e | 2.62 d | 5,357 abc |
| 6 | Alto fl oz/A 5.5 (1); Elatus fl oz/A 7.3 (2, 3) | 5.62 de | 5.62 cd | 5,807 a |
| 7 | Bravo weather stik 24 fl oz (1); Lucento 5.5 fl oz (2, 3) | 5.25 de | 6.88 cd | 5,669 ab |
| 8 | Miravis 3.4 fl oz (2, 3) | 2.12 e | 2.00 d | 5,335 abc |
| 9 | Elatus 7.3 fl oz (2, 3) | 9.12 cd | 7.88 cd | 5,720 ab |
| 10 | Umbra 25 fl oz (1, 2) | 20.17 b | 23.71 b | 5,190 bc |
| 11 | Umbra 38 fl oz (1, 2) | 19.00 bc | 19.63 bc | 5,321 abc |
1 Timing corresponds to the spray dates of 1=July 16, 2=July 31, 3=Aug. 21, 4=Sept. 12.
2 Means within a column followed by the same letter are not significantly different, according to Tukey’s HSD test (α = 0.05).
* Data was transformed using the square root for inference (ANOVA assumptions), but means are presented on the original scale.
| Treatment Number | Product, Rate, Timing1 | Early Leaf Spot (%)2 - Oct. 2** | Defoliation (%)2 - Oct. 2* | Yield (lbs./A)2 |
|---|---|---|---|---|
| 1 | Untreated check | 33.80 a | 39.40 a | 4,951 b |
| 2 | Lucento 5.5 fl oz (1, 3); Bravo weather stik 24 fl oz + Tebuzol 7.2 fl oz (2) | 4.12 ef | 3.38 d | 5,422 ab |
| 3 | Adastrio 9 fl oz (1, 3); Bravo weather stik 24 fl oz + Tebuzol 7.2 fl oz (2) | 4.50 ef | 4.50 d | 5,589 a |
| 4 | Bravo weather stik 24 fl. oz + Tebuzol 7.2 fl oz (2); Abound flowable 18.5 fl oz (3,4) | 9.75 cde | 10.20 cd | 5,822 a |
| 5 | Alto 5.5 fl oz (1); Miravis fl oz/A 3.4 (2 & 3) | 2.62 f | 2.62 d | 5,662 a |
| 6 | Alto fl oz/A 5.5 (1); Elatus fl oz/A 7.3 (2 & 3) | 7.62 cde | 7.12 cd | 5,677 a |
| 7 | Bravo weather stik 24 fl oz (1); Lucento 5.5 fl oz (2, 3) | 3.62 ef | 4.38 d | 5,640 a |
| 8 | Miravis 3.4 fl oz (2, 3) | 4.38 def | 5.00 cd | 5,466 ab |
| 9 | Elatus 7.3 fl oz (2, 3) | 12.20 bcd | 14.60 bc | 5,452 ab |
| 10 | Umbra 25 fl oz (1,2) | 20.60 ab | 24.40 ab | 5,219 ab |
| 11 | Umbra 38 fl oz (1,2) | 14.20 bc | 14.50 bc | 5,510 ab |
1 Timing corresponds to the spray dates of 1=June 26, 2=July 16, 3=Aug. 21.
2 Means within a column followed by the same letter are not significantly different, according to Tukey’s HSD test (α = 0.05).
* Data was transformed using the square root for inference (ANOVA assumptions), but means are presented on the original scale.
** Data was transformed using log1p for inference (ANOVA assumptions), but means are presented on the original scale.