Abstract
The interplay of management decisions involving soybean (Glycine max L.) planting date, herbicide programs, and herbicide application timings is critical to optimize soybean performance and weed control in Southern Great Plains soybean production systems. This research sought to evaluate soybean yield potential and the level of weed control as influenced by early-, delayed-, and late- planting dates and various combinations of preemergence (PRE), early-postemergence (EPOST), and mid-postemergence (MPOST) weed management programs. A field study was established in Bixby, OK in 2017 and 2018 under irrigated conditions and in Perkins, OK in 2017 under dryland conditions, consisting of three planting windows (early, delayed, and late) of XtendFlex soybean, with or without a PRE (chlorimuron + flumioxazin + pyroxasulfone + glyphosate + dicamba) combined with EPOST or EPOST + MPOST (glyphosate + dicamba) versus no in-season applications. The gap in late-planted soybean yield potential, compared to early-planted soybean, was exacerbated in the dryland systems (1346 kg ha-1) versus an irrigated system (2311 kg ha-1). Use of PRE provided 60% weed control until MPOST and increased yields by 657 kg ha-1 and 457 kg ha-1 for delayed and late-planted soybean, respectively. Late-planted soybean with EPOST + MPOST provided up to 50% weed control, but lack of biomass production for cultural control reduced weed control by 29% compared to early- and delayed-planted soybean. From an agronomic management standpoint, the time of soybean planting is influential on the success of weed control measures and soybean yields in double-cropping system in the Southern Great Plains, particularly with late-planted soybean.
Application of preemergence resulted in greater yields of late-planted soybean in dryland and irrigated conditions. Herbicide programs ending at early-postemergence provided adequate weed control across early and delayed plantings. Late-planted soybean produced less biomass and required multiple postemergence applications for adequate weed control.
