Evaluation of the Impact of Fungicide Application Timing on Soybean (Glycine max) Growth, Development, and Yield.

Disease pressure is one of the major constraints of profitable soybean production. This has driven the practice of preventative fungicide applications to manage foliar pathogens that may negatively influence yield. Previous research in Mississippi has reported a 201.6 to 403.2 kilogram per hectare yield increase from a preventative fungicide applied at the R3 growth stage. The objective of this research is to determine if delaying the application of a preventative fungicide to later soybean growth stages results in a similar yield increase as observed following the traditional R3 growth stage timing.

Experiments were conducted in 2017 and 2018 at the R.R. Foil Plant Science Research Center near Starkville, MS and the Delta Research and Extension Center near Stoneville, MS in 2018. The experimental design was a factorial arrangement of treatments within a randomized complete block. Treatments consisted of five application timings, using three different fungicide options, with an untreated check for comparison purposes. Fungicide treatments included Quadris_® (Azoxystrobin), Quadris Top_® SBX (Azoxystrobin, Difenconazole), and the combination of Priaxor_® (Fluxapyroxad, Pyraclostrobin) and Domark_® (Tetraconazole). Fungicides were applied in single applications at the R3, R4, R5, or R6 growth stages, along with a two-pass application program at R3 followed by R5 using a backpack sprayer equipped with a handheld boom containing Teejet Turbo Twinjet 11002 spray tips.

Results indicate soybean receiving an application of Quadris Top SBX or Priaxor + Domark yielded greater when compared to soybean that did not receive a fungicide application. Applications of Quadris showed no significant differences when compared to the untreated check. In addition, timing of fungicide application showed no significance when applied at any growth stage. These data suggest that delaying a preventative fungicide application to later soybean growth stages resulted in the same yield advantage as observed following the traditional R3 growth stage timing.