Early-season Lactofen application has limited effect on soybean branch and mainstem yield components

Recent interest in maximizing soybean [Glycine max (L.) Merr.] yield has led producers to seek management strategies to affect soybean yield components. One strategy that has been pursued is application of diphenyl ether herbicides, such as lactofen, to early-vegetative soybean to kill the apical meristem in an effort to increase soybean branching, resulting in increased node and pod numbers. The objective of this study was to determine if the application of lactofen and fomesafen herbicides can kill the soybean apical meristem and quantify how earlyseason application of these herbicides affect soybean yield components. Field studies were established at two locations in Kentucky during the 2013 and 2014 growing seasons. Lactofen, fomesafen, leaf removal, and meristem removal treatments were applied to soybean at first, second, third, and fourth trifoliate stages. Plants were harvested at maturity and nodes, pods, and seeds per square meter and seed mass were determined for both mainstem and branches. Meristem removal increased soybean branch development and shifted yield component formation from the mainstem nodes to branch nodes. Lactofen and fomesafen had small and inconsistent effects on mainstem and branch yield components compared with untreated soybean but did not affect total yield components. Lactofen and fomesafen were not able to kill the apical meristem or increase branching in soybean. Attempting to increase soybean node number through agronomic management does not appear to be a viable strategy to increase soybean yield.