Effect of foliar fungicides on frogeye leaf spot management in Northwestern Maryland, 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 Western Maryland Research and Education Center in Keedysville, 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-tilled into soybean residue at 140,000 seeds/A on 5 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 7 Jul. Treatments with subsequent applications were made 14 days later on 21 Jul. 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 3 Sept. Plant greenness (normalized differential vegetation index, NDVI) was measured at three points during pod fill on 3, 9, and 24 of Sept using a handheld GreenSeeker. 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 18 Nov. Data were analyzed using ANOVA and significant differences between treatments were separated using Fisher’s Least Significant LSD (LSD; α=0.10).
Even in a relatively dry year when the research station received only 20 in. of rain from 1 May to 1 Nov, FLS was a prevalent disease. All fungicide treatments significantly reduced FLS severity compared to the non-treated control, with plots receiving two applications of Miravis Top or two applications of Priaxor having significantly less FLS disease severity than plots that received a single application of either product. No significant differences in yield were detected, which may be attributed to the overall low yield in the trial due to drought-like growing conditions encountered throughout the season. No phytotoxicity was observed with any of the fungicide treatments. All fungicides affected plant greenness during senescence at the two earliest NDVI ratings compared to the non-treated control (α=0.10). 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 |
NDVIʸ 3 Sept. |
NDVI 9 Sept. |
NDVI 24 Sept. |
Green stemˣ (%) | Yield (bu/A) |
|---|---|---|---|---|---|---|
| Miravis Top 1.67SC, 13.7 fl oz at R1 | 42 cʷ | 0.86 a | 0.75 a | 0.36 | 10.6 a | 36.6 |
| Miravis Top 1.67SC, 13.7 fl oz at R1 fb Miravis Top 1.67SC, 13.7 fl oz 14 days after R1 |
16 a | 0.85 ab | 0.76 a | 0.37 | 13.4 a | 36.2 |
| Priaxor 4.17SC, 8 fl oz at R1 | 30 bc | 0.84 bc | 0.76 a | 0.37 | 4.7 b | 36.0 |
| Priaxor 4.17SC, 8 fl oz at R1 fb Priaxor 4.17SC, 8 fl oz 14 days after R1 |
20 a | 0.86 a | 0.78 a | 0.38 | 11.5 a | 37.2 |
| Non-treated control | 88 d | 0.83 c | 0.66 b | 0.27 | 1.6 b | 31.1 |
| p-value | <0.0001 | 0.0509 | 0.0091 | 0.1458 | 0.0007 | 0.4757 |
ᶻ FLS= Frogeye leaf spot. Percentage of infect tissue on upper 1/3 of soybean canopy assessed at R6.
ʸ NDVI= Normalized Difference Vegetation Index; plant greenness rated during pod fill and plant senescence.
ˣ Green stem= Percentage of green stem plants at maturity (R8) rated from center 4 rows of each plot.
ʷ 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