Impact of Fungicide Application Timing on Soybean (Glycine max) Yield in Mississippi.

In the mid-southern U.S., the use of a preventative fungicide application at the R3 growth stage is a common practice for yield loss prevention in soybean. Previous research in Mississippi has reported a 3 to 6 bushel yield increase from an automatic R3 fungicide application. The objective of this research is to determine if delaying the timing of an automatic fungicide application to later growth stages results in similar yield observed following applications at the R3 timing.

An experiment was conducted in 2017 at the R.R. Foil Plant Science Research Center near Starkville, MS. A total of 16 treatments were arranged in a randomized complete block design and 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.

Preliminary results indicate soybean receiving an application of Quadris Top SBX at the R3, R4, or R5 growth stages yielded greater when compared to soybean that did not receive a fungicide application. In addition, soybean yield was greater following the two-pass program of Quadris Top SBX when compared to all fungicides applied in a single application at the R6 growth stage as well as the untreated check. When fungicides were applied at the R6 growth stage, no soybean yield differences were observed when compared to the untreated. Experiments will be repeated in 2018 to further evaluate soybean yield response of fungicide application at these timings.