Weeds belonging to the Amaranthus family are most problematic for soybean producers. With Palmer amaranth evolving resistance to multiple herbicides labeled for use in soybean, producers seek new sites of action to integrate into season-long herbicide programs. Bayer CropScience plans to launch a Convintro™ brand of herbicides, one being a premixture that will include diflufenican (WSSA Group 12), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15), for use preemergence (PRE) in soybean. Research trials were conducted in Fayetteville and Keiser, AR, and Holt, MI, in 2022 and 2023 to evaluate the premixture in a season-long program in a dicamba-resistant soybean system. A 0.17:0.35:0.48 of the diflufenican:metribuzin:flufenacet (DFF-containing) premixture was applied PRE with different combinations of glyphosate, glufosinate, dicamba, and acetochlor at 28 [early-postemergence (EPOST)] and 42 [late-postemergence (LPOST)] days after planting (DAP). At the EPOST timing, the DFF-containing premixture provided >90% Palmer amaranth and prickly sida control. However, common ragweed, common lambsquarters, morningglory ssp., and annual grass control was ≤80% at this timing. When the LPOST applications occurred, treatments that had already received an EPOST application controlled prickly sida, morningglory ssp., Palmer amaranth, and annual grasses greater than those that had not, indicating the PRE application of the DFF-containing premixture was not sufficient to provide control of the weed spectrum through 42 days after planting. By 70 days after planting, all programs provided ≥93% control of all weeds evaluated. Herbicide programs that utilized the DFF-containing premixture PRE fb EPOST fb LPOST controlled common ragweed, common lambsquarters, morningglory ssp., and annual grasses greater than the one pass postemergence systems. In addition, all herbicide programs evaluated reduced Palmer amaranth seed production by >99%. However, producers that plan to utilize the DFF-containing premixture may need two postemergence herbicide applications to obtain high levels of weed control throughout the growing season.

Bayer CropScience anticipates launching several premixtures for use in soybean, targeted at control of Palmer amaranth. One of the premixtures will contain diflufenican (WSSA Group 12), metribuzin (Group 5), and flufenacet (Group 15) (DFF-containing premixture), offering an alternative site of action for soybean producers. Field experiments were conducted in Arkansas and Michigan to evaluate application timings of the DFF-containing premixture for soybean tolerance and weed control and possible cultivar tolerance differences to diflufenican and the DFF-containing premixture. Soybean injury from the 1X and 2X rates of the DFF-containing premixture ranged from 0% to 60% 14 d after planting (DAP), with injury increasing the closer the herbicide was applied to soybean emergence. Excluding the 2X rate applied 3 DAP in Arkansas in 2023, soybean injury was <20% regardless of location, site year, application timing, and rate. For weed control experiments, only a 1X rate of the DFF-containing premixture was applied at the various application timings. Control of five weed species, encompassing broadleaves and grasses, ranged from 81% to 98%, regardless of application timing by 28 DAP. By 42 DAP, weed control ranged from 71% to 97%, with the 14-d preplant application timing typically being the least effective. The DFF-containing premixture and diflufenican alone were applied PRE at 1X and 2X rates for the soybean cultivar study. Soybean metribuzin sensitivity did not affect the degree of crop response, even on a high pH soil, and injury to soybean never exceeded 20%. Overall, the DFF-containing premixture will be a tool that soybean producers can integrate into a season-long herbicide program for use across the United States regardless of the soybean cultivar.