Dicamba plus glyphosate tank mixture have been largely adopted for postemergence weed control after the development of dicamba-tolerant crops. Ammonium sulfate is commonly used as water conditioner (WC) to increase glyphosate efficacy, but its use is restricted for dicamba herbicides. The use of non-AMS water conditioner and other adjuvants could be a way to optimize efficacy of this tank mixture while mitigating herbicide off-target movement. The objective of this study was to determine the physical–chemical properties and droplet size distribution of dicamba and glyphosate solutions with and without non-AMS WC alone and tank mixed with other adjuvants and evaluate the response of weed species to these solutions under greenhouse and field conditions. The adjuvants mostly increased density and viscosity and decreased contact angle and surface tension of herbicide solutions. In presence of WC, except for the adjuvants containing drift reducing agent, Dv_0.5 decreased with the addition of adjuvants. Under greenhouse conditions, biomass reduction increased up to 47 and 33 percentage points for velvetleaf and c. waterhemp when adjuvants were added to solutions without WC, respectively. No increase in control of horseweed and Palmer amaranth was observed with the use of adjuvants under field conditions.

Glufosinate efficacy is inconsistent among weed species and under environmental conditions that favor rapid droplet drying. Surfactant‐humectant adjuvants could maximize glufosinate efficacy by increasing wetting and penetration into the leaf surface while decreasing evaporation rate (ER). However, there is a lack of information in the literature about the interaction of surfactant‐humectants adjuvants with glufosinate. The objective of this study was to investigate the influence of surfactant‐humectant adjuvants on the physical properties, droplet size, and efficacy of two glufosinate formulations. Laboratory, greenhouse, and field studies were conducted at the Pesticide Application Technology Laboratory of the University of Nebraska‐Lincoln. Treatment design was a 2 × 5 factorial with two glufosinate formulations combined with five adjuvant treatments plus an untreated control. Density and viscosity of glufosinate solutions mostly increased with the addition of adjuvants. However, the influence of the adjuvants on dynamic surface tension (dST), static contact angle (sCA), and evaporation rate (ER) varied by glufosinate formulation, adjuvant, and relative humidity (RH). Under greenhouse conditions, an improvement in efficacy by adding adjuvants was mainly observed for Interline solutions. The addition of adjuvants to Interline solutions increased biomass reduction up to 19 and 35% for common lambsquarters (Chenopodium album L.) and kochia [Bassia scoparia (L.) A. J. Scott], respectively. Also, some of the adjuvants presented null or antagonistic influence on herbicide efficacy. No increase in control, biomass reduction, and mortality of horseweed (Erigeron canadensis L.) and Palmer amaranth (Amaranthus palmeri S. Watson) was observed with the use of adjuvants under field conditions. Herbicide‐adjuvant‐plant‐environment interaction is complex. Thus, the use of surfactant‐humectant adjuvants may not increase herbicide efficacy.

Sorgoleone, an allelochemical exuded from root hairs of grain sorghum [ Sorghum bicolor (L.) Moench], has proven herbicidal activity on several weeds and crops. Due to its hydrophobic nature and affinity for organic matter, sorgoleone can persist in the soil for a long period. Although sorghum residues are beneficial for weed suppression, growers in the southeastern United States have raised concerns that these residues may negatively affect wheat ( Triticum aestivum L.) emergence in double-crop systems. Two independent laboratory studies were conducted to evaluate sorgoleone activity: (1) weed species/wheat variety study, which included four weed species, Italian ryegrass [ Lolium perenne L. ssp. multiflorum (Lam.) Husnot], large crabgrass [ Digitaria sanguinalis (L.) Scop.], sicklepod [ Senna obtusifolia (L.) Irwin & Barneby], and velvetleaf [ Abutilon theophrasti Medik.], and two wheat varieties, ‘USG3251’ and ‘Shirley’; and (2) wheat variety and group study, which included a total of 20 varieties distributed in four wheat groups. In both studies, sorgoleone was applied at 0.025, 0.05, 0.10, 0.15, 0.20, and 0.30 g L ⁻¹ to seeds grown in petri dishes under laboratory conditions. In Study 1, sorgoleone activity had a stronger effect on grass weeds than on broadleaf weeds. Lolium perenne ssp. multiflorum was the most susceptible weed, showing 77% growth reduction at 0.3 g L ⁻¹ of sorgoleone. At the same concentration, D. sanguinalis showed the second-highest response, with a 32% growth reduction, followed by A. theophrasti and S. obtusifolia , with reductions of 23% and 20%, respectively. No effect of sorgoleone was observed on wheat varieties. In Study 2, growth reduction was only observed for six wheat varieties at the highest sorgoleone concentrations. Furthermore, in between group comparisons, Hard Red wheat presented higher response to sorgoleone. These findings demonstrate strong herbicidal activity of sorgoleone on grass weeds, particularly L. perenne ssp. multiflorum , while having minimal effects on most wheat varieties.

Dicamba and 2,4-D are postemergence herbicides widely used to control broadleaf weed species in crop and non-crop areas in the United States. Currently, multiple formulations of 2,4-D and dicamba are available on the market. Even though the active ingredient is the same, the chemical formulation may vary, which can influence the volatility potential of these herbicides. Therefore, the objective of this study was to evaluate the response of soybean, cotton, and tobacco plants exposed to vapors of 2,4-D and dicamba formulations alone or mixed in humidomes for 24 h. Humidome studies were conducted in an open pavilion at the Lake Wheeler Turfgrass Field Lab of the North Carolina State University in Raleigh, NC. Dicamba and mixture treatments injured and caused a reduction in the height of soybean. Injury varied from 55% to 70%, and average plant height was 8.8 cm shorter compared with untreated control plants. Treatments with 2,4-D caused the least injury to soybean (≤21%), and differences among formulations were identified (dimethylamine > choline > dimethylamine-monomethylamine). However, soybean height was not affected by 2,4-D treatments. No differences between treatments were observed when herbicides were applied to cotton. The greatest injury to tobacco (23.3%) was caused by dicamba dimethylamine. Overall, the effect of 2,4-D and dicamba vapor was species-specific and formulation-dependent. Additionally, environmental conditions in the humidomes may have played a major role on the outcome of this study.

Dicamba plus glyphosate (DpG) tank mixture has been widely adopted for broad-spectrum weed control. However, recent studies indicated antagonistic interactions between these herbicides. Furthermore, little is known about the effect of non-ammonium sulfate water conditioner (non-AMS WC) adjuvant on the activity of DpG tank mixture. Thus, the present study was elaborated to evaluate (1) the interaction of DpG tank mixtures combinations on barnyardgrass, and glyphosate-susceptible (GS) and -resistant (GR) horseweed control, and (2) the effect of non-ammonium sulfate water conditioner (non-AMS WC) on the interaction of those two herbicides on the aforementioned weed species. Greenhouse experiments were conducted in 2020 at the Pesticide Application Laboratory in North Platte, NE. Herbicide treatments were arranged in a two-level factorial design of six dicamba rates by six glyphosate rates for Study 1, and in a three-level factorial design of two adjuvant treatments (presence or not of non-AMS WC) by four dicamba rates by four glyphosate rates for Study 2. Both trials were conducted as randomized complete block designs with four replications and two runs. Antagonistic interactions were observed throughout DpG treatments in GS and GR horseweed. For instance, dicamba (560 g ae ha⁻¹) and glyphosate (1260 g ae ha⁻¹) resulted in 72% of GR horseweed biomass reduction, compared to 81% of estimated biomass reduction. For barnyardgrass, antagonistic interactions were only observed within the reduced glyphosate rates. The addition of non-AMS WC had no effect on DpG antagonism. However, it improved the barnyardgrass control by glyphosate.

Triclopyr is a synthetic auxin herbicide widely used to manage roadside vegetation due to its effective, selective, and prolonged action on broadleaf species, as well as its low toxicity to humans and animals. However, if triclopyr drifts from the roadside into agricultural lands, it can result in injury and yield loss of sensitive crops. The objective of this study was to characterize and quantify particle and vapor drift of triclopyr as influenced by formulation, season, and nozzle type under roadside conditions. Field studies were conducted on a roadside located along Interstate 540 in Morrisville, NC, in 2022 and 2023. Triclopyr amine and choline were applied at 3363 g a.e. ha ⁻¹ using Boominator and Nutating nozzles. Active air samplers were used to collect vapor drift within 48 h after application, while deposit cards were used to collect particle drift 10 min after application. Triclopyr vapor concentration peaked within the first 24 h after application, with the concentration of triclopyr amine being 29% higher than triclopyr choline during this period. Additionally, vapor concentrations of triclopyr were higher during spring and summer compared to fall and winter. No differences in triclopyr particle deposit and drift distance were observed between formulation and nozzle type. Triclopyr was detected at very low levels (< 2% of field rate) within 3 m from the treated area. This study provides valuable insight into triclopyr volatilization, emphasizing temporal, formulation, and seasonal variations, while also addressing the consistency in particle drift between triclopyr formulations and nozzle types.