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 early‐season 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.

Soybean producers have recently adopted management systems that attempt to manipulate plant stress throughout the growing season in an effort to increase yield. The purpose of this study was to determine if management systems that utilize crop inputs to manipulate soybean stress can increase soybean seed yield. Inputs designed to affect soybean stress were applied to early‐maturity (2.8 relative maturity [RM]) and full‐season (4.5 RM) soybean at three locations in Kentucky throughout the 2013 and 2014 growing seasons. Treatments consisted of a single application, sequential applications, or combined applications of the following inputs: lactofen, lambda‐cyhalothrin with thiamethoxam, pyraclostrobin, and N,N’‐diformyl urea. The full‐season soybean yielded greater (19%) than the early‐season soybean, resulting from an increase in mainstem node, pod, and seed numbers. Lactofen decreased early season light interception in all environments but did not affect soybean yield. None of the stress‐management inputs investigated increased yield compared to untreated soybeans. Soybean stress management through prophylactic input application does not appear to be a viable strategy to increase soybean yield.

Abbreviations:UTC, untreated control; DAE, days aft er emergence; MG, maturity group. Core Ideas• Leaf removal and lactofen application decrease early-season light interception in soybean. • Destroying the soybean apical meristem either decreases or does not aff ect soybean yield. • Lactofen application to early vegetative soybean does not increase yield under weed free conditions.

Core Ideas Early‐season stress can increase or decrease seed protein. Early‐season stress can increase or decrease seed oil. Changes in protein and oil were inconsistent across years and sites.