Estefania Gomiero Polli

Herbicides are one of the primary tools for vegetation management along roadsides. However, the drift of particles and vapors from herbicide applications along roadsides can cause damage and yield loss in adjacent sensitive crops. The objective of this research was to investigate the response of soybean [ Glycine max (L.) Merr.] and tobacco ( Nicotiana tabacum L.) to sublethal rates of five herbicides [sulfometuron‐methyl, indaziflam, triclopyr, triclopyr + clopyralid, and 2,4‐dichlorophenoxyacetic acid (2,4‐D) + dichlorprop] commonly used along North Carolina roadsides. Each herbicide was applied at four rates (0.01×, 0.05×, 0.10×, and 1× of the field rate) and at six different timings (18, 12, and 6 weeks before planting or transplanting, at planting or transplanting, and 4 and 8 weeks after planting or transplanting). Field studies were conducted at the Sandhills Research Station near Jackson Springs, NC, in 2022 and 2023. In soybean, triclopyr applied post‐planting caused the greatest injury and yield loss, up to 100% when applied at the full dose (1×), while indaziflam was most damaging at or before planting. In tobacco, triclopyr followed by 2,4‐D + dichlorprop applied post‐transplanting caused the greatest injury and height reduction, whereas indaziflam caused mild visual injury (≤28%) and minimal height reduction across all timings. Crop damage generally increased with rate; however, injury, height reduction, and yield loss were occasionally observed even at the lowest rate (0.01×). These findings demonstrate that herbicides commonly used for roadside vegetation management differ in their potential to injure soybean and tobacco crops, underscoring the importance of informed and cautious herbicide selection to minimize the risk of off‐target injury when these crops are grown near roadsides.

Herbicide spray drift from roadside application sites poses risks of damaging nearby sensitive crops. The objective of this research was to investigate the impact of five herbicides (sulfometuron‐methyl, indaziflam, triclopyr, triclopyr + clopyralid, and 2, 4‐D + dichlorprop) commonly used to manage roadside vegetation at four application rates (0.01x. 0.05x, 0.1x, and 1x of the field rate) and six application timings (18, 12, and 6 weeks before planting, at planting, and 4 and 8 weeks after planting) on corn ( Zea mays L.) and cotton ( Gossypium hirsutum L.). Field studies were conducted at Upper Coastal Plain Research Station in Rocky Mount, NC, in 2022 and 2023. Although herbicide sensitivity varied by crop species, both species presented higher levels of injury and stunting for application conducted at planting and early post‐planting, and at higher rates. In corn, sulfometuron‐methyl caused the greatest damage. When applied at 4 weeks after planting, this herbicides caused injury of 100% and 48%, and height reduction of 66% and 16%, at 0.1x and 0.01x rates, respectively. In cotton, synthetic auxin herbicides, particularly 2, 4‐D + dichlorprop and triclopyr, were the most damaging post‐emergence. For instance, 2, 4‐D + dichlorprop applied 4 weeks after planting at the 0.01× rate caused 78% injury and 25% height reduction. This study highlights the importance of herbicide selection and application timing when spraying along roadsides to minimize the risk of spray drift damaging nearby corn and cotton fields.

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.

Dazomet is a fumigant commonly used to control soil seedbanks and plant tissues of weed species in highly infested turfgrass areas. This fumigant reacts with water in the soil when in the presence of oxygen and releases methyl isothiocyanate (MITC) gas that kills seeds and plant tissues within the soil. Previous studies have reported varying levels of weed control by dazomet. As MITC is highly water soluble, mobile in soil, and volatile, inconsistencies in dazomet efficacy may be related to post-application practices of tilling, rolling, irrigation, and tarping. Therefore, the objective of this study was to analyze the effect of two practices commonly performed following dazomet application: tarp treatment (tilling, rolling, irrigation, and tarping), and water-seal treatment (post-irrigation at 0, 1, 2, and 3 days after application) on MITC concentration, distribution, and persistence in sandy soil. Field studies were conducted at Sandhills Research Station in Jackson Springs, NC, USA, in 2022 and 2023. MITC concentration and persistence varied between treatments and years. In 2022, MITC concentrations were notably higher in the tarp treatment compared with the water-seal treatment, whereas in 2023, the difference between treatments was less pronounced and more soil depth– and sample timing–dependent. Both treatments presented longer persistence, up to 168 hours after application (HAA), in 2023 compared with 120 HAA in 2022. In addition, MITC was highly concentrated in the top 15 cm of the soil and was detected as deep as 31 cm down from the soil surface in both treatments across both years.

Herbicides are a primary tool for vegetation management along roadsides. However, herbicide drift from roadside applications can cause damage and yield loss in sensitive crops nearby. The objective of this research was to investigate the response of soybean and tobacco to simulated drift of five herbicides - sulfometuron-methyl, indaziflam, triclopyr, triclopyr + clopyralid, and 2,4-D + dichlorprop - commonly used along North Carolina roadsides. Each herbicide was applied at four rates (0.01x, 0.05x, 0.10x, and 1x the field rate) and six application timings (18, 12, 6 before plant, at plant, and 4 and 8 weeks after plant). Field studies were conducted at the Sandhills Research Station near Jackson Springs, NC, in 2022 and 2023. Sulfometuron-methyl and indaziflam caused the most damage in soybean at pre-plant and at plant application timings, with yield loss ranging from 20% to 29% and 24 to 33%, respectively. For post-plant application, triclopyr was the most damaging herbicide, resulting in 76% to 80% yield loss. Similar, in tobacco, sulfometuron-methyl caused the most damage at pre-plant (16-24%). Additionally, triclopyr and 2,4-D + dichlorprop caused the greatest damage post-plant, leading to 69% to 76% and 44% to 53% injury, respectively. Crop damage generally increased with higher rates, although damage was observed even at the lowest rates. This research confirms the need for careful consideration of herbicide application when soybean and tobacco are grown close to where these herbicides are used for roadside vegetation management.

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.

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.

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.

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.