Auxin-Based Herbicide Program and Rhizobia Application for Weed Control and Nodulation Potential in Auxin Tolerant Soybean

Foliar-applied Bradyrhizobia to V4 soybean has been reported to increase yield up to 5%. However, a stand-alone product application may not be practical. Applying with other treatments such as post-emergence herbicide application may be economical but herbicide and/or additives may be deleterious to rhizobial growth. A laboratory study investigated the impact of herbicides (glyphosate and dicamba), additives (an oil to improve absorption and spreading; and AMS used to overcome hard water impacts on glyphosate), and herbicide + additives on bacterial growth. Optical density (OD) measurements at the wavelength of 650 nm assessed solution turbidity, a surrogate measure of bacterial growth. Glyphosate, dicamba, and AMS, as stand-alone treatments, reduced OD values by 98, 64 and 100%, respectively, compared to control (deionized water + inoculant) after 72-hr. Herbicide + additives, however, had OD values 25 % greater than the control. Therefore, applying bradyrhizobia with post-emergence herbicide applications at labeled rates with typical mixtures of surfactants/additives should not be harmful to the bacteria. Field experiments were conducted at three South Dakota locations for two years where Enlist E3 or Xtend soybean varieties were planted early, mid, or late season. Treatments included preemergence (pre), pre + post emergence auxin herbicides (2,4-D or dicamba), or herbicide solutions mixed with bradyrhizobia to examine weed control, soybean nodulation and activity, yield, and seed protein. Pre-only herbicides resulted in poor weed control and reduced yields. Pre + post emergence treatments improved weed control and yield, with early and mid-planting having greater yields than late planting. Uncontrolled weeds in the pre and pre + auxin-based treatments were mostly grasses including barnyardgrass (Echinochloa crus-galli), volunteer wheat (Triticum aestivum), large crabgrass (Digitaria sanguinalis), green foxtail (Setaria viridis) and volunteer corn (Zea mays). Rhizobia application did not impact soybean nodulation, yield, or seed protein in 27 out of 30 treatments. The exception was dicamba + glyphosate + rhizobia that enhanced nodulation numbers (+30%) and activity (+54%) in one location in one year for all three planting dates compared to dicamba + glyphosate, although yield and seed protein content were similar among these treatments

Herbicide and Additive Impacts on \u3cem\u3eBradyrhizobium japonicum\u3c/em\u3e Growth in Solution

Plant biostimulants include beneficial fungi and bacteria, and are often applied to foliage to improve crop growth, yield, and/or crop quality. Crop improvements due to biostimulant addition may be modest; therefore, solo applications may not be economical or climate smart. However, biostimulants combined with other postemergence treatments, such as herbicides, may provide an alternative application method, if mixtures do not harm the living organism(s). The growth of Bradyrhizobium japonicum, as a biostimulant surrogate, was assessed in solutions of glyphosate [N-(phosphonomethyl)glycine] and dicamba (3,6-dichloro-2-methoxybenzoic acid), with and without common spray additives (ammonium sulfate [AMS] and nonionic surfactant) in laboratory studies over 72 h. Solution turbidity, using optical density as a surrogate of bacterial growth, was measured at 600 nm at 24, 48, and 72 h after inoculation, and colony forming units (CFUs) per milliliter were estimated. Growth was not detected in either the glyphosate or AMS solutions, most likely due to the low pH and high electrical conductivity of the solutions, respectively. When herbicides were mixed with a nonionic surfactant, CFUs per milliliter were about 25% greater than the positive control. These data suggest that mixing bacteria with postemergence herbicide + surfactants/additives combinations can hinder or maintain growth when preparing for agrochemical applications. Biostimulant type and the agrichemical combination(s) should be evaluated prior to tank mixing to determine if detrimental interactions occur. After application, an evaluation of the effectiveness of the biostimulant to the crop and efficacy of the agrichemical to the target organism should be conducted

Auxin-based Herbicide Program for Weed Control in Auxin Resistant Soybean

Soybean [Glycine max (L.) Merr.] cultivars resistant to synthetic auxin herbicides have provided another mode of action for the postemergence broadleaf weed control. This field study was conducted at three South Dakota locations [Northeast, NERF; east-central, ARF; and Southeast, SERF) in 2019 and two locations (ARF and SERF) in 2020. The Enlist E3 and Roundup Ready 2 Xtend cultivars were planted at three dates (early, mid-, and late season) to examine weed control, agronomic characteristics, nodulation, and yield. Preemergence (PRE) treatment was flumioxazin + metribuzin + S-metolachlor + glyphosate + pendimethalin. Two postemergence (POST) treatments, based on cultivar, were compared with PRE-only. The PREonly treatment had numerous grasses {including green foxtail [Setaria viridis (L.) P. Beauv.] and yellow foxtail [S. pumila (Poir.) Roem. & Schult.], volunteer corn (Zea mays L.), barnyard grass [Echinochola crus-galli (L.) Beauv.], large crabgrass [Digitaria sanguinalis (L.) Scop.], woolly cupgrass [Eriochloa villosa (Thunb.) Kunth]} and broadleaf weeds (including redroot pigweed [Amaranthus retroflexus L.], common lambsquarters [Chenopodium album L.], waterhemp [Amaranthus rudis Sauer]) with high density and biomass. POST treatments controlled most of the broadleaf species, although some grasses remained. Yields were similar within a location and year, although differences occurred among planting dates. In 2019, planting date did not influence final yield at ARF (average yield 3,084 kg ha−1). Yield was greatest for the early (NERF) and mid-planting dates (NERF and SERF) compared with late-season planting. In 2020, dry conditions occurred, and yields at ARF and SERF were lowest for the late-season plantings (ranging from 37 to 73% lower depending on cultivar) compared with the early season planting. In 2020, dicamba + glyphosate treatment of the Xtend cultivar had 10% (ARF) and 20% (SERF) greater yield than the acifluorfen + clethodim treatment

Herbicide and additive impacts on Bradyrhizobium japonicum growth in solution

Abstract Plant biostimulants include beneficial fungi and bacteria, and are often applied to foliage to improve crop growth, yield, and/or crop quality. Crop improvements due to biostimulant addition may be modest; therefore, solo applications may not be economical or climate smart. However, biostimulants combined with other postemergence treatments, such as herbicides, may provide an alternative application method, if mixtures do not harm the living organism(s). The growth of Bradyrhizobium japonicum, as a biostimulant surrogate, was assessed in solutions of glyphosate [N‐(phosphonomethyl)glycine] and dicamba (3,6‐dichloro‐2‐methoxybenzoic acid), with and without common spray additives (ammonium sulfate [AMS] and nonionic surfactant) in laboratory studies over 72 h. Solution turbidity, using optical density as a surrogate of bacterial growth, was measured at 600 nm at 24, 48, and 72 h after inoculation, and colony forming units (CFUs) per milliliter were estimated. Growth was not detected in either the glyphosate or AMS solutions, most likely due to the low pH and high electrical conductivity of the solutions, respectively. When herbicides were mixed with a nonionic surfactant, CFUs per milliliter were about 25% greater than the positive control. These data suggest that mixing bacteria with postemergence herbicide + surfactants/additives combinations can hinder or maintain growth when preparing for agrochemical applications. Biostimulant type and the agrichemical combination(s) should be evaluated prior to tank mixing to determine if detrimental interactions occur. After application, an evaluation of the effectiveness of the biostimulant to the crop and efficacy of the agrichemical to the target organism should be conducted