Efficacy of tiafenacil applied preplant alone or mixed with metribuzin for glyphosate-resistant horseweed control in soybean

Abstract

Tiafenacil is a recently developed protoporphyrinogen IX oxidase (PPO)-inhibiting herbicide from the pyrimidinedione chemical class that is proposed for use as a preplant (PP) burndown in soybean. Glyphosate-resistant (GR) horseweed is a troublesome weed often found in no-till systems that can dramatically reduce soybean yield; control in soybean has been variable. Five field experiments were conducted over 2019 and 2020 in commercial soybean fields with GR horseweed to determine the biologically-effective-dose (BED) of tiafenacil and tiafenacil + metribuzin, and to compare their efficacy to currently accepted industry standard herbicide treatments in identity-preserved (IP, non-GMO), GR, and glyphosate/dicamba-resistant (GDR) soybean systems. There was no soybean injury with treatments evaluated. The calculated doses of tiafenacil for 50, 80, and 95% control of GR horseweed control were 21, 147 and >200 g ai ha−1, respectively, at 8 weeks after application (WAA). Lower doses were calculated with the addition of metribuzin (400 g ai ha−1) to tiafenacil for 50 and 80% control, with no dose of tiafenacil + metribuzin providing 95% control. Tiafenacil + metribuzin at 25 + 400 and 50 + 400 g ai ha−1 controlled GR horseweed 88 and 93% , respectively which was similar to the industry standards of saflufenacil + metribuzin (25 + 400 g ai ha−1) and glyphosate/dicamba + saflufenacil (1200/600 + 25 g ai ha−1) that provided 98 to 100% control, respectively at 8 WAA. This study presents the potential utility of tiafenacil + metribuzin as a GR horseweed management strategy in soybean.

Tolerance of White Bean to Tiafenacil Herbicide Mixtures and Control of Multiple Herbicide-Resistant Horseweed With Tiafenacil Herbicide Mixtures

“…At 2, 4, and 8 WAA, there was no soybean injury from the PP herbicides evaluated (data not shown). This is consistent with other studies conducted with glyphosate + tiafenacil or saflufenacil, another PPO-inhibitor herbicide applied PP in a mixture with other herbicides in soybean (Miller et al, 2012;Budd et al, 2016aBudd et al, , 2016bWesterveld et al, 2021).…”

“…pha -1 in soybean. Westerveld et al (2021) observed 55-66% GR horseweed control with glyphosate + tiafenacil (900 + 25 g a.i. per ha -1 ) applied PP, and 87-90% GR horseweed control with glyphosate + tiafenacil + metribuzin (900 + 25 + 400 g a.i.…”

“…per ha -1 ) applied PP caused no visible black bean injury and no reduction in stand or yield. Control of weeds, especially MHR horseweed has not been consistent with the co-application of glyphosate (C 3 H 8 NO 5 P) + tiafenacil (Soltani et al, 2021b;Westerveld, 2021;Westerveld et al, 2021). Earlier studies have shown that glyphosate + tiafenacil applied PP provides only 51-68% control of MHR horseweed in soybean (Soltani et al, 2021b).…”

Improving the Level and Consistency of Glyphosate-Resistant Canada Fleabane (Erigeron canadensis L.) Control With Bromoxynil-Based Tankmixes Applied Preplant to Soybean

“…Glyphosate plus metribuzin, pyraflufen-ethyl/2,4-D, 2,4-D ester, halauxifen-methyl, saflufenacil or dicamba reduced GR Canada fleabane density 78, 68, 82, 88, 90, and 85%, respectively; density was not reduced with glyphosate plus tiafenacil. Similar reductions in GR Canada fleabane density have been reported in previous research (Budd et al, 2016;Eubank et al, 2008;Soltani et al, 2020a;Westerveld et al, 2021c;Zimmer et al, 2018b). When bromoxynil was added to glyphosate plus metribuzin, tiafenacil or pyraflufen-ethyl/2,4-D GR Canada fleabane density was reduced 7, 22, and 20%, respectively; density was not reduced when bromoxynil was added to glyphosate plus 2,4-D ester, halauxifen-methyl, saflufenacil or dicamba.…”

The Addition of Saflufenacil to Glyphosate plus Dicamba Improves Glyphosate-Resistant Canada Fleabane (Erigeron canadensis L.) Control in Soybean

“…Adding tiafenacil to glyphosate + dicamba did not improve GRCF control at 2, 4, or 8 WAA, and there was no reduction in density or biomass relative to glyphosate + dicamba (Table 4). Recent research by Westerveld et al [39] reported similar results with no improvement in GRCF control when adding tiafenacil (25 g ai ha −1 ) to glyphosate (900 g ae ha −1 ) + metribuzin (400 g ai ha −1 ) at 2, 4 and 8 WAA. In their study, there was also no decrease in GRCF density or biomass relative to glyphosate (900 g ae ha −1 ) + metribuzin (400 g ai ha −1 ).…”