Early Season Lactofen Application Effects on Soybean Yield and Yield Components.

Recently high soybean prices have led producers to consider intensive management strategies to maximize yields and profits.  These include herbicide applications to the crop for perceived benefits other than weed control.  For example, it has been suggested that protoporphyrinogen oxidase (PPO) inhibitor herbicides applied to young soybeans can directly increase yields.  It is hypothesized that these herbicides damage the soybean apical meristem stimulating increased lateral branching thereby increasing the number of reproductive nodes and potential yield.  However, there is limited published evidence supporting increased lateral branching in soybean after PPO herbicide application.  To test the hypothesis of increased lateral branching and increased soybean yield following PPO herbicide applications, a small plot-study was conducted in 2013 and 2014 at three locations in Kentucky.  The study was arranged in a randomized complete block design and maintained weed free.  Herbicides (lactofen at 240 g ai ha^-1 or fomesafen at 600 grams ai ha^-1) were applied at the V1, V2, V3 and V4 soybean growth stages.  Treatments for comparison were an untreated control, a treatment where the soybean apical meristems were manually removed, and a treatment where all the leaves were removed.  These latter two treatments were performed at the same growth stages as herbicide applications.  Data collected at harvest included, mainstem nodes plant^-1,branch nodes plant^-1, pods plant ^-1, pods branch^-1, seeds m^-2, seed mass, and seed yield.  Removal of the apical meristem increased branch nodes plant^-1 but did not increase seed yield when compared to the untreated control.  Herbicide treatments did not affect branch nodes plant^-1 or soybean seed yield.  Leaf removal at all growth stages decreased seed yield by 5% across all locations.  These results indicate that early season lactofen application to soybeans does not lead to increased branching and seed yield.