Early-Season lactofen application fails to increase soybean yield under weed-free conditions

In an effort to increase soybean [Glycine max (L.) Merr.] yield, growers may consider non-traditional use of crop inputs. One non-traditional input use is the application of lactofen {2-ethoxy-1-methyl-2-oxoethyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate} herbicide to early-vegetative soybean to promote increased branch development and ultimately increase seed yield. The purpose of this study was to evaluate the effect of early-season lactofen application and simulated herbicide injury on stands, plant height, light interception, and seed yield. The experiments were conducted at two locations in Kentucky during the 2013 and 2014 growing seasons. Treatments included lactofen herbicide applied at 240 g a.i. ha^–1 and fomesafen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-N-methylsulfonyl-2-nitrobenzamide} herbicide applied at 600 g a.i. ha^–1. A meristem removal treatment was included, where the apical meristem of each soybean was physically removed, and a leaf removal treatment was also performed. All treatments were applied to soybean at V1, V2, V3, and V4 growth stages. The herbicide application timing had no effect on any of the above mentioned agronomic measurements. The apical meristem removal reduced plant stands and plant height in 2 site-years while lactofen and leaf removal decreased early-light interception in all site-years. Meristem removal and leaf removal reduced seed yield in 1 site-year, while lactofen, leaf removal, and meristem removal reduced seed yield in another site-year. None of the treatments increased seed yield compared with the untreated control. Despite a limited number of trials, this study suggests that application of lactofen to soybean for non-weed control purposes is not a viable strategy to increase soybean yield.