Title : Critical time for weed removal in soybean as influenced by pre emergence herbcides
Abstract:
By definition, the critical timing for weed removal (CTWR) is the maximum amount of time early season weed competition can be tolerated by the crop before the crop becomes subject to an irrevocable yield reduction. The concept of CTWR has been shown to be useful tool for determining the timing of weed control operations in agronomic crops. However, it has been speculated that CTWR can be influenced by the production practices. Therefore, field experiments were conducted in 2015 and 2016 at Concord, Nebraska, to evaluate the CTWR in soybean, as influenced by pre-emergence (PRE) herbicides. The studies were laid out in a split-plot arrangement with herbicide regime as the main plot and weed removal timing as the subplot. The herbicide regimes included; without PRE-herbicide and premix of saflufenacil plus imazethapyr at the rate of 280 g ai ha-1 or 420 g ai ha-1. The weed removal timings were at V1, V3, V6, R2 and R5 soybean stages, as well as weed free and weedy season-long control. The CTWR was based on 5% acceptable yield loss. CTWR started at V1 soybean stage (21 days after emergence (DAE)) without PRE herbicide, while the application of PRE-herbicide delayed the CTWR to V5 soybean stage (34 DAE) in 2015 and to R1 soybean stage (46 DAE) in 2016. These results suggested that the use of PRE-herbicide in soybeans could delay the need for postemergence weed control by 2 to 5 weeks. Keywords: Weeds, Pre-emergence, Post-emergence, critical, time
