Effect of foliar fungicides on frogeye leaf spot on the Maryland Eastern Shore, 2020
Editor’s note: Data from 2020 is presented here since 2021 trials are not yet harvested. 2021 results will be posted to the Agronomy News Blog.
Trials were established at the Wye Research and Education Center in Queenstown, MD in 2020 to assess the efficacy of select fungicides for the suppression of foliar diseases of soybean. Soybean Mid-Atlantic ‘MAS4077GT/STS’ were no-till direct-seeded into soybean residue at 140,000 seeds/A on 15 May using a 10-foot no-till drill set on 7.5-in. row spacing. Plots were 30 feet long and established in a randomized complete block design with five replications and data collection occurred from the center five feet of each plot. Soybean cultivation practices were consistent with recommendations from the University of Maryland Extension. The trial consisted of four foliar fungicide treatments and a non-treated control. Fungicide applications were applied with a backpack CO2 sprayer with TeeJet 8003 nozzles calibrated to deliver 20 GPA at 35 psi to the center 80 in. of each plot. Fungicides were applied at the R1 growth stage on 15 Jul. Treatments with subsequent applications were made 14 days later on 29 Jul. Based on the disease history of the field and lack of rotation out of soybean, natural pathogen inoculum levels were utilized for disease infection. Disease severity from frogeye leaf spot (FLS; Cercospora sojina) was visually rated as the percent leaf area infected in the upper canopy from the center four rows of each plot at the R6 growth stage on 7 Sept. Green stem ratings were collected at maturity (R8) by counting the number of green stem plants (not mature color) from 10 random plants from the center four rows of each plot. Yield was collected by harvesting the center five feet of each plot and data reported are adjusted to 13% moisture. Plots were harvested on 20 Nov. Data were analyzed using ANOVA and significant differences between treatments were separated using Fisher’s Least Significant LSD (LSD; α=0.10).
Nearly 48 in. of precipitation accumulated from 1 May to 1 Nov, 2020, resulting in heavy FLS disease pressure. Plots treated with Miravis Top at R1, Miravis Top at R1 followed by Miravis Top 14 days after, and Priaxor at R1 followed by Priaxor 14 days after resulted in significantly less FLS severity than the non-treated control and the single application of Priaxor. Both Miravis Top treatments improved yield compared to all other treatments (α=0.10). No phytotoxicity was observed with any of the fungicide treatments. All fungicide treatments, with the exception of Priaxor at R1, significantly increased incidence of green stem at harvest compared to the non-treated control.
| Treatment, rate/A and timing | FLSᶻ % severity |
Green stemʸ (%) | Yield (bu/A) |
|---|---|---|---|
| Miravis Top 1.67SC, 13.7 fl oz at R1 | 12 aˣ | 20 a | 50.7 a |
| Miravis Top 1.67SC, 13.7 fl oz at R1 fb Miravis Top 1.67SC, 13.7 fl oz 14 days after R1 |
10 a | 40 a | 47.2 ab |
| Priaxor 4.17SC, 8 fl oz at R1 | 42 b | 12 b | 42.2 bc |
| Priaxor 4.17SC, 8 fl oz at R1 fb Priaxor 4.17SC, 8 fl oz 14 days after R1 |
16 a | 24 a | 40.3 c |
| Non-treated control | 46 b | 8 b | 42.0 bc |
| p-value | <0.0001 | 0.0007 | 0.0816 |
ᶻ FLS= Frogeye leaf spot. Percentage of infect tissue on upper 1/3 of soybean canopy assessed at R6.
ʸ Green stem= Percentage of green stem plants at maturity (R8) rated from center four rows of each plot.
ˣ Means followed by the same letter are not significantly different based on Fisher’s Least Significant Difference (LSD; α=0.10).
This work was sponsored by the Maryland Soybean Board.
This article appears on November 2021, Volume 12, Issue 8 of the Agronomy news.