Economics of reducing Palmer amaranth seed production in dicamba/glufosinate/glyphosate‐resistant soybean

Abstract

Increased prevalence of glyphosate-resistant (GR) weeds within agronomic cropping systems has led to the readoption of pre-emergence (PRE) herbicides and use of multiple herbicide-resistant soybean [Glycine max (L.) Merr.] cultivars. Herbicide programs were evaluated in the recently commercialized dicamba/glyphosate/glufosinate-resistant (DGGR) soybean for weed control, reduction of Palmer amaranth (Amaranthus palmeri S. Watson) seed production, crop safety, and economic performance. At 35 days after pre-emergence herbicides, acetochlor plus dicamba plus metribuzin, acetochlor/fomesafen plus dicamba, dicamba plus flumioxazin, and imazethapyr/pyroxasulfone/saflufenacil provided 80-99% control of velvetleaf (Abutilon theophrasti Medik.), Palmer amaranth, common lambsquarters (Chenopodium album L.), and Poaceae species. Evaluation at 14 days after early postemergence herbicides indicated PRE followed by (fb) POST applications of mixtures of acetochlor, dicamba, glufosinate, and glyphosate provided 80-99% weed control compared with 67-93% control in POST-only programs. Most herbicide programs provided 83-99% control of grass and broadleaf weeds, with 85-91% weed biomass reductions at 28 days after late-POST. The PRE fb POST programs reduced Palmer amaranth seed production by 94-99%, whereas POST-only programs provided 75-83% reduction. In 2020, most programs provided gross profit margins ≥US$1,000 ha −1 , with glufosinate fb glufosinate and imazethapyr/pyroxasulfone/saflufenacil fb acetochlor plus glufosinate providing $1,481 and $1,466 ha −1 , respectively. Benefit/cost ratios ranged between 0.3 and 3.9 in 2019 due to hail but increased to 2.9-10.9 in 2020. Results of this study support use of PRE herbicides with multiple sites of action in DGGR soybean and indicate that glufosinate can provide POST control of GR Palmer amaranth.

Comparison of residual activity of pre‐emergence herbicides for control and seed production of multiple herbicide‐resistant Palmer amaranth in food‐grade white corn

“…At 30 DAPRE, almost all residual herbicides recorded 1–3 plants m ‒2 apart from atrazine (15 plants m ‒2 ) and atrazine/bicyclopyone/mesotrione/ S ‐metolachlor (11 plants m ‒2 ). Striegel and Jhala (2022) reported that PRE herbicide reduced glyphosate‐resistant Palmer amaranth density to 0–1 plant m −2 compared with nontreated plots (26 plants m −2 ). Whitaker et al.…”

“…Thus, a PRE fb a POST herbicide program has a better chance of reducing MHR Palmer amaranth seed production compared with relying only on PRE herbicide. Striegel and Jhala (2022) reported that glyphosate‐resistant Palmer amaranth seed production declined to 0–325 seeds plant ‒1 when PRE herbicide was used compared with POST‐only programs (85–4786 seeds plant ‒1 ) in soybeans and further reduced to 0 seeds plant ‒1 when a PRE herbicide was followed by a POST herbicide with residual activity.…”

“…(2016) reported that mesotrione and isoxaflutole applied to PRE were effective for control of glyphosate‐resistant Amaranthus spp. Striegel and Jhala (2022) indicated that acetochlor plus dicamba plus metribuzin, acetochlor/fomesafen plus dicamba, dicamba plus flumioxazin, and imazethapyr/pyroxasulfone/saflufenacil provided 94%–98% control of herbicide‐resistant glyphosate‐resistant Palmer amaranth at 35 DAPRE in dicamba/glufosinate/glyphosate‐resistant soybean.…”

“…Inman et al (2020) reported that acetochlor plus diuron plus fomesafen applied PRE provided 79% glyphosate-resistant Palmer amaranth control at 2-3 weeks after planting. Striegel and Jhala (2022) elaborated on the use of PRE herbicides for control of glyphosate-resistant Palmer amaranth (94%-98% 35 DAPRE) in dicamba/glufosinate/glyphosate-resistant soybean and concluded that PRE herbicides have a positive effect on soybean yield. Thus, if MHR Palmer amaranth is a major weed in growers' field, the use of PRE herbicides with multiple effective sites of action is almost mandatory for early season control to avoid competition with crops (Ward et al, 2013).…”

4-Hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides: past, present, and future

“…More specifically, multi-tactic strategies that target multiple life stages of the weed, including understanding reproductive biology and potential for pollen-mediated gene flow, are required (Jhala et al 2021a(Jhala et al , 2021b. This can be accomplished by using an effective multiple-sites-of-action herbicide program, using cover crops, planting corn or soybean in narrow rows, using a harvest weed seed control method, and adopting diversified crop rotations (Mohler et al 2021;Striegel and Jhala 2022). The increasing use of HPPD-inhibitor herbicides in agronomic crops requires research on herbicide interactions and alternative herbicides or methods for controlling multiple herbicide-resistant weeds.…”