Influence of Application Timings and Sublethal Rates of Synthetic Auxin Herbicides on Soybean

Abstract

Synthetic auxin herbicides have long been utilized for the selective control of broadleaf weeds in a variety of crop and noncrop environments. Recently, two agrochemical companies have begun to develop soybean with resistance to 2,4-D and dicamba which might lead to an increase in the application of these herbicides in soybean production areas in the near future. Additionally, little research has been published pertaining to the effects of a newly-discovered synthetic auxin herbicide, aminocyclopyrachlor, on soybean phytotoxicity. Two field trials were conducted in 2011 and 2012 to evaluate the effects of sublethal rates of 2,4-D amine, aminocyclopyrachlor, aminopyralid, clopyralid, dicamba, fluroxypyr, picloram, and triclopyr on visible estimates of soybean injury, height reduction, maturity, yield, and yield components. Each of these herbicides was applied to soybean at the V3 and R2 stages of growth at 0.028, 0.28, 2.8, and 28 g ae ha−1. Greater height reductions occurred with all herbicides, except 2,4-D amine and triclopyr when applied at the V3 compared to the R2 stage of growth. Greater soybean yield loss occurred with all herbicides except 2,4-D amine when applied at the R2 compared to the V3 stage of growth. The only herbicide applied that resulted in no yield loss at either stage was 2,4-D amine. When applied at 28 g ae ha−1at the V3 stage of growth, the general order of herbicide-induced yield reductions to soybean from greatest to least was aminopyralid > aminocyclopyrachlor = clopyralid = picloram > fluroxypyr > triclopyr > dicamba > 2,4-D amine. At the R2 stage of growth, the general order of herbicide-induced yield reductions from greatest to least was aminopyralid > aminocyclopyrachlor = picloram > clopyralid > dicamba > fluroxypyr = triclopyr > 2,4-D amine. Yield reductions appeared to be more correlated with seeds per pod than to pods per plant and seed weight. An 18- to 26-d delay in soybean maturity also occurred with R2 applications of all synthetic auxin herbicides at 28 g ae ha−1except 2,4-D. Results from this research indicate that there are vast differences in the relative phytotoxicity of these synthetic auxin herbicides to soybean, and that the timing of the synthetic auxin herbicide exposure will have a significant impact on the severity of soybean height and/or yield reductions.

Drift of 2,4-D and dicamba applied to soybean at vegetative and reproductive growth stage

“…The degree of injury observed in soybean for 2,4-D and dicamba herbicides were similar to those observed in soybean (GRIFFIN et al, 2013;ROBINSON et al, 2013aROBINSON et al, , 2013bSOLOMON & BRADLEY, 2014). Soybean exhibited the greatest symptoms injury to 2,4-D between 26 and 32% for V 5 and R 2 stages at high rate, respectively ( Figure 1).…”

“…applied during reproductive stages (GRIFFIN et al, 2013;SOLOMON & BRADLEY, 2014). Although, 2,4-D exposure to the V 5 soybean stage influenced more than V 2 and R 2 stage (ROBINSON et al, 2013b).…”

“…Although, 2,4-D exposure to the V 5 soybean stage influenced more than V 2 and R 2 stage (ROBINSON et al, 2013b). Previous research has documented that synthetic auxins herbicides drift onto sensitive soybean can cause many negative effects, such as reduction of seed weight, lower seed quality, lower seed oil and protein concentration, pod malformation and impacts on progeny (ROBINSON et al, 2013a(ROBINSON et al, , 2013bSOLOMON & BRADLEY, 2014;KESOJU et al, 2016;MILLER & NORSWORTH, 2017).…”

Response of Soybean Offspring to a Dicamba Drift Event the Previous Year

“…Dicamba is a phloem-mobile herbicide (Senseman 2007), meaning that when applied it will inherently move to areas of new growth. Soybean exposure to dicamba in the vegetative stage resulted in greater injury compared with reproductive-stage exposure (Griffin et al 2013;Kelley et al 2005;Solomon and Bradley 2014;Weidenhamer et al 1989). Kelley et al (2005) Weed Technology cambridge.org/wet Research Article Cite this article: Jones GT, Norsworthy JK, Barber T (2019) Response of soybean offspring to a dicamba drift event the previous year.…”

Comparison of Simulated Drift Rates of Common ALS-Inhibiting Rice Herbicides to Florpyrauxifen-Benzyl on Soybean

“…Symptomology can vary from chlorosis of the terminal buds, cupping or crinkling of canopy leaves, and leaf or stem epinasty. Higher rates can even result in stem cracking, terminal death, or plant death [17,21,22]. The risk of crop injury and potential yield loss will perhaps be greatest to growers who choose not to be aware of crops in surrounding fields or who choose not to use resistant varieties in regions where these varieties and associated herbicide programs are widely adopted by neighboring farmers [23].…”