Triclopyr Butoxyethyl Ester Research Articles

Physical and physiological pathways of off-target triclopyr movement and associated non-target injury following basal bark application

AbstractBasal bark treatment with triclopyr butoxyethyl ester is used to control woody invasive plants, including Brazilian peppertree (Schinus terebinthifolia Raddi). However, the ester formulation cannot be applied where standing water is present, which includes wetlands where S. terebinthifolia is found. In 2009, a low-volatile acid formulation of triclopyr was labeled for use in aquatic sites, which allows for basal bark applications when standing water is present. This formulation may have utility for controlling woody plants in standing water. However, anecdotal observations of injury to non-target plants following applications during periods of inundation have been reported. To address this, mesocosm studies were conducted to assess non-target injury through triclopyr root exudation or release from the surface of treated stems via flooding. Mesocosms contained S. terebinthifolia as the treated target, while sugarberry (Celtis laevigata Willd.), buttonbush (Cephalanthus occidentalis L.), and red maple (Acer rubrum L.) were included as non-targets. In the first study, the pathway of root exudation for non-target injury following triclopyr (34 g L−1) basal bark application was isolated with activated charcoal placed at the soil surface. In the second study, mesocosms were flooded to assess triclopyr release from the surface of treated stems and subsequent non-target injury. Defoliation of non-target species posttreatment was ≤8%, and triclopyr was detected at ≤5 µg L−1 in mesocosm wells when activated charcoal was present. Posttreatment non-target defoliation up to 92%, coupled with triclopyr concentrations in surface waters and wells as high as 4,637 µg L−1, indicated triclopyr movement as a result of flooding. Additionally, triclopyr non-target injury from soil activity independent of flooding was observed. These findings provide limited evidence of triclopyr root exudation but considerable evidence of triclopyr release during flooding following basal bark treatment and support a cautionary approach to basal bark application when standing water is present.

Novel basal bark and cut stump herbicide treatments for Brazilian peppertree (Schinus terebinthifolia) management

AbstractBrazilian peppertree (Schinus terebinthifolia Raddi) is an aggressive shrub that infests more than 280,000 ha in Florida. Individual plant treatments (IPT), including basal bark and cut stump application with triclopyr butoxyethylester and triethylamine formulations, respectively, have been used for decades. While they are both effective, resprouting can occur, which requires retreatment for control. Recent research on other woody invasive plants has indicated additional non-crop herbicides used in natural areas can be effective with these IPT techniques and therefore warrant testing on S. terebinthifolia. In 2018 and 2019, basal bark and cut stump studies were conducted at Cape Canaveral Air Force Station in natural areas infested with S. terebinthifolia. In the basal bark application studies, we found aminocyclopyrachlor applied at 12 and 24 g L−1 and triclopyr acid applied at 34 and 69 g L−1 each provided 100% defoliation of multistemmed S. terebinthifolia individuals with a mean root collar diameter up to 20.2 cm at 360 d after treatment (DAT). These were not different from triclopyr ester applied at 96 g L−1. Imazamox applied at 30 g L−1 resulted in 86% defoliation at 360 DAT. However, we observed formulation incompatibility when imazamox was mixed with basal bark oil which may limit its utility. In cut stump studies, we found aminocyclopyrachlor and aminopyralid each individually applied at 6, 12, and 24 g L−1, resulted in stump mortality that was not different from the commercial standard triclopyr amine applied at 180 g L−1. Similar results were found for a triclopyr acid formulation applied at 86 and 172 g L−1 and imazamox applied at 60 g L−1. For both treatment techniques, we found that alternative treatments provided control at lower herbicide concentrations than triclopyr ester and amine commercial standards. These results advance our understanding of IPT and expand access to additional effective herbicide options for S. terebinthifolia management.

Response of black swallowwort (Vincetoxicum nigrum) to herbicides plus mowing

AbstractThe invasive vine black swallowwort [Vincetoxicum nigrum (L.) Moench = Cynanchum louiseae Kartesz & Gandhi, Apocynaceae] is difficult to control, and herbicide studies are lacking. This long-lived perennial species is primarily found in high-light environments in natural areas and perennial cropping systems in northeastern North America. We conducted a 3-yr herbicide efficacy study, with or without mowing, in an old-field site infested with V. nigrum in Dutchess County, NY, USA. Experimental plots were either herbicide treated in early July or mowed in early July and subsequently herbicide treated in late August for 2 yr with the potassium salt of glyphosate (2.02 kg ae ha−1), the isopropylamine salt of glyphosate (1.35 kg ae ha−1), or the butoxyethyl ester of triclopyr (1.79 kg ae ha−1). Both glyphosate formulations were effective in reducing V. nigrum aboveground biomass, although they were somewhat less effective in reducing cover or stem densities of V. nigrum plants >10-cm tall after 2 yr compared with untreated plots. Mowing did not always enhance the efficacy of foliar glyphosate applications. Triclopyr, with or without mowing, was generally not effective against V. nigrum in our study. The only significant effect of triclopyr was to increase the cover of grasses in the plots. While annual applications of glyphosate can be useful for management of V. nigrum infestations, higher rates and more frequent applications of triclopyr need to be investigated to determine its usefulness for V. nigrum control.

Developmental toxicity studies on triclopyr acid, triclopyr butoxyethyl ester and triclopyr triethylamine salt in the rabbit

Developmental toxicity studies have been conducted in the rabbit on triclopyr acid and its active-ingredient variants, triclopyr triethylamine salt (T-TEA) and triclopyr butoxyethyl ester (T-BEE), which are dissociated or hydrolysed in vivo to triclopyr acid. In this paper, the available developmental toxicity studies on triclopyr acid, T-TEA and T-BEE are summarised and evaluated. For triclopyr acid and T-TEA, there was no evidence of impaired reproductive performance, fetotoxicity, or teratogenicity, even at maternally toxic doses. The no-observed-adverse-effect levels (NOAELs) for developmental toxicity were 75 mg/kg bw per day for triclopyr acid and 100 mg/kg bw per day for T-TEA, equivalent to 72 mg/kg bw per day expressed as triclopyr acid. A study on T-BEE showed increased post-implantation loss and slight increases in skeletal anomalies and variants at the highest dose tested of 100 mg/kg bw per day, a maternally toxic dose. In a follow-up study on T-BEE, focusing on post-implantation loss, no general increase in post-implantation loss was observed, but one animal at 100 mg/kg bw per day with maternal toxicity had complete resorption of implants. The NOAEL for post-implantation loss was 60 mg/kg bw per day, equivalent to 44 mg/kg bw per day expressed as triclopyr acid. It cannot be excluded that T-BEE may be associated with increased post-implantation loss, but it was only seen in association with maternal toxicity. It is concluded that triclopyr acid and its variants are not specifically toxic to the rabbit embryo and fetus, since post-implantation loss only occurred at doses causing maternal toxicity.

Reproductive and developmental evaluations of triclopyr acid, triclopyr butoxyethyl ester and triclopyr triethylamine salt in the rat

Reproductive and developmental toxicity studies have been conducted in rat and rabbit on triclopyr acid and its active-ingredient variants, triclopyr butoxyethyl ester (T-BEE) and triclopyr triethylamine salt (T-TEA). In this paper the results of a rat two-generation study on triclopyr acid are presented, together with a review of all the reproductive and developmental toxicity data available from the rat studies. In the rat two-generation study, triclopyr acid was administered in the diet, giving doses of 0, 5, 25 or 250 mg/kg bw per day. Parental toxicity, especially maternal toxicity, occurred at 250 mg/kg bw per day with reduced body weight and feed intake, organ weight changes, and kidney toxicity. Slight kidney toxicity was also evident at 25 mg/kg bw per day. Developmental toxicity, in the form of reduced postnatal survival in the F1 and F2 generations and reductions in pre-weaning offspring body weight in both generations, was seen only at a dose causing significant parental toxicity. There were no effects on any other reproductive or developmental parameters at any dose. It is concluded that the developmental toxicity, seen only at the highest dose, was most likely attributable to maternal toxicity. The no-observed-adverse-effect levels were 5 mg/kg bw per day for parental toxicity and 25 mg/kg bw per day for developmental toxicity. From the multigeneration and developmental toxicity studies on triclopyr and its variants, it can also be concluded that triclopyr is not specifically toxic to reproduction and is not selectively toxic to the embryo, fetus or neonate in the rat.

Estimated herbicide use in the commercial forest sector in South Africa

ABSTRACT This paper examines herbicide use in South African commercial plantations in 2017/18 across three climate zones (cool temperate − CT, warm temperate − WT and subtropical − ST) for three genera (eucalypts, pines and acacias) grown for two end-products (sawn timber and pulpwood). Herbicide information was obtained from 46 timber plantations owned by six forestry companies, comprising 343 872 ha surveyed. The herbicide survey was divided into three climate zones due to increased vegetation growth (and hence more herbicide use) on more productive ST sites compared to moderately productive WT sites, with the lowest vegetation growth on CT sites (lower productivity). The survey was further divided into three distinct vegetation management phases associated with plantation forestry (pre-establishment, re-establishment and post-establishment) to compare herbicide use between genera grown on an annual basis. A total of 188 288 kg (or 0.55 kg ha−1) of herbicide active ingredient (a.i.) was applied in the area surveyed. Glyphosate-based products accounted for 97% of all the herbicides applied, and metazachlor and triclopyr butoxy ethyl ester accounted for 2%. Overall, herbicide use per hectare on an annual basis was highest in the ST zone, followed by the WT and CT zones. For both the CT and WT zones, the general trend was that the pre-establishment phase received noticeably more herbicides, followed by the re- and post-establishment phases (prerepost). This trend remained similar for the genera grown (prerepost), with hardwoods receiving more herbicides than softwoods. In contrast, there was little difference in herbicide use between the re- and pre-establishment phases for the ST zone, with the post-establishment phase being noticeably less. Besides providing benchmark data related to herbicide use in South African plantations, future research should investigate the potential for a reduction in herbicide use in those regions, vegetation management phases and management regimes where it is highest.

Efficacy of triclopyr and synthetic auxin herbicide mixtures for common blue violet (Viola sororia) control

AbstractCommon blue violet is a widely distributed, perennial broadleaf that is difficult to control in lawns. Two experiments were conducted to evaluate the efficacy of synthetic auxin herbicides and their mixtures or rate for common blue violet control. A herbicide comparison experiment was conducted with treatments including a nontreated check; 2,4-D dimethylamine; 2,4-D isooctyl ester (2,4-D ester); dichlorprop (2,4-DP) ethylhexyl ester, MCPA dimethylamine; mecoprop dimethylamine; triclopyr butoxyethyl ester; quinclorac; and mixtures of triclopyr + quinclorac; 2,4-D ester + 2,4-DP; 2,4-D ester + triclopyr; 2,4-D ester + 2,4-DP + triclopyr. All herbicides were applied at 1.12 kg ae ha−1except quinclorac (0.84 kg ha−1). Additionally, a triclopyr dose-response experiment was conducted using rates of 0, 0.14, 0.28, 0.56, 0.84, and 1.12 kg ha−1. Epinasty ranged from 80% to 99% at 21 d after application for triclopyr-containing treatments and no more than 28% for all other treatments. Plant mass from harvest and regrowth data from the comparison experiment indicated triclopyr-containing treatments provided the highest common blue violet control. Mixtures containing triclopyr did not differ from triclopyr alone, indicating there was no added effect between herbicide mixtures. The triclopyr dose-response experiment confirmed triclopyr efficacy across data collection types. As triclopyr dose increased, violet epinasty increased and chlorophyll content and dry weight decreased. Triclopyr applied at 0.81 kg ha−1or greater concentration provided 75% or greater control, as indicated by regrowth data. Many herbicides containing triclopyr are registered for use in turf, but most apply a concentration not greater than 0.56 kg ha−1triclopyr when applied at the high label rate. Thus, to achieve good (75%) common blue violet control, turf managers should select products that contain triclopyr and apply doses of at least 0.81 kg ha−1when used according to the label.

Hyperspectral VNIR-spectroscopy and imagery as a tool for monitoring herbicide damage in wilding conifers

Wilding conifers, the naturally regenerated scions of exotic conifer species, are a major ecological and economic issue in New Zealand. Hyperspectral imagery could provide a useful means of monitoring the efficacy of wilding control measures but little research has examined this possibility. Data were collected from an experiment, that included thirty-nine young Pinus contorta (Douglas) trees allocated to a control and two herbicide treatments (triclopyr butoxyethyl ester and diquat dibromide monohydrate). The objectives of this research were to examine the temporal impacts of herbicide on needle discolouration, spectral properties and tree physiology and to develop models to predict photosynthetic parameters from hyperspectral data. In accordance with obvious discolouration on the first day after treatment, values of net photosynthesis rate (A), electron transport rate (ETR), stomatal conductance (G) and optimal quantum yield of photosystem II (Fv/Fm) declined rapidly for plants treated with diquat. Discolouration following application of triclopyr was not evident before the second week, and values of A, ETR, G and Fv/Fm declined slower than those of diquat. Of the tested narrow-band spectral indices calculated from needle spectra photochemical reflectance index (PRI) exhibited the strongest correlation with the four photosynthetic parameters and R2 values between PRI and A, Fv/Fm, ETR and G were, respectively, 0.53, 0.46, 0.68 and 0.29. Models that used raw spectra as inputs showed that sparse partial least squares (SPLS) outperformed the three other approaches tested (PLS, Support Vector Machines, Elastic Net) and R2 values using this approach for A, Fv/Fm, ETR and G were, respectively, 0.64, 0.62, 0.65 and 0.42.

Triclopyr Application Timing and Concentration Influence Low-Volume Basal Bark Efficacy on Chinese Privet (Ligustrum sinense)

Chinese privet is an invasive shrub that commonly infests roadsides and bottomland forests across the southeastern United States. Its aggressive growth and ability to prolifically sprout from the root collar and shallow lateral roots makes control very difficult. Individual plant treatment methods such as low-volume basal bark herbicide application with triclopyr are commonly used for Chinese privet control. However, little research has been done to examine optimal triclopyr concentrations and application timings for the low-volume basal bark method. Furthermore, little is known regarding basal bark treatment efficacy when plant size varies. To address these questions, field studies were conducted from 2009 to 2011 at two locations in east-central Alabama near Auburn and Opelika. The triclopyr butoxyethyl ester formulation was applied in January or March to Chinese privet shrubs across a range of sizes in a commercially available basal oil carrier at 24 (5% v/v−1), 48 (10% v/v−1), and 96 g L−1(20% v/v−1). Additionally, a triclopyr butoxyethyl ester ready-to-use formulation (90 g L−1) was applied at 100% v/v−1. Canopy defoliation, sprout height, and mortality were quantified at 6, 12, and 18 mo after treatment. Triclopyr at all concentrations was highly effective in defoliating Chinese privet and reducing height of new basal sprouts. However, mortality was concentration dependent. The 90 and 96 g L−1treatments resulted in 88 and 89% mortality across timings, while the 24 and 48 g L−1treatments resulted in 63 and 76% mortality. March applications were less effective as basal diameter increased, especially at the lower triclopyr concentrations where mortality fell to less than 40%. These results indicate that triclopyr is an effective treatment for Chinese privet control, but efficacy is influenced by concentration, application timing, and plant size.

Dermal Absorption Read-Across for Agrochemicals: A Case Study with Triclopyr Formulations Using In Vitro Human Studies

Dermal absorption data are required on agrochemical formulations to conduct risk assessments for subpopulations who may be exposed dermally to the formulation and/or its spray dilution, for example, operators/sprayers, bystanders (incidental and residential), and re-entry workers. In the absence of formulation-specific data, the European Food Safety Authority (EFSA) guidance proposes highly conservative default values and very limited opportunities for read-across to existing data. In this case study, data from GLP and OECD 428 test guideline-compliant in vitro dermal absorption studies using human skin for 5 formulations containing triclopyr-butoxyethyl ester (BEE) were analyzed to develop triclopyr-specific read-across approach. Four emulsifiable concentrate and one emulsion-in-water formulations were tested as “concentrates” (undiluted product; concentration range was 90–240 gacidequivalent(a.e.)/L) and/or as 1 or 2 representative “spray dilutions” (product diluted with water; concentration range was 0.3–10.3 g(a.e.)/L). Worst-case dermal absorption values (according to EFSA guidance calculations) ranged between 1% and 4% for the concentrates and 8% and 20% for the spray dilutions. Increases in percentage dermal absorption were seen with decreased triclopyr-BEE concentration, but these were not linear. Logarithmic functions describe the absorption trend with concentration for the concentrates (R2=0.8505), spray dilutions (R2=0.7993), or both (R2=0.9439). Human in vivo dermal absorption data available for one of the above formulations showed consistency with the in vitro data. This case study demonstrates that an existing dataset for an active substance may be used for read-across purposes for an untested formulation as an alternative approach to testing.

Field Evaluation of Auxin Herbicide Volatility Using Cotton and Tomato as Bioassay Crops

Research was conducted to compare cotton and tomato response to volatility of 2,4-D, dicamba, and triclopyr formulations. Herbicide treatments were applied to tilled soil during August and September, and potted plants were placed in the center of treated strips. To quantify injury, leaf cupping/crinkling/drooping; leaf rolling/strapping; stem epinasty; and stem swelling/cracking were each visually rated on an injury scale of 0 to 5 (0 = none, 1 = slight, 2 = slight to moderate, 3 = moderate, 4 = moderate to severe, and 5 = severe). Leaf cupping/crinkling/drooping injury averaged across herbicide treatments at 1× rates was 1.0 for cotton and 2.0 for tomato 14 d after treatment (DAT). Averaged across crops, leaf cupping/crinkling/drooping injury for the 1× rates 14 DAT was equivalent for the 2,4-D dimethylamine (DMA) salt, 2,4-D acid, dicamba DMA salt, dicamba diglycolamine (DGA) salt, dicamba acid, and triclopyr acid formulations and ranged from 1.1 to 1.8. For tomato, the only herbicide treatments with injury 14 DAT no greater than for the nontreated were 1× rates of 2,4-D DMA and 2,4-D acid for leaf rolling/strapping (1.0); 2,4-D acid, dicamba DMA, dicamba acid, and triclopyr acid for stem epinasty (0.3 to 0.7); and 2,4-D DMA, 2,4-D acid, dicamba DMA, dicamba DGA, dicamba acid, and triclopyr acid for stem swelling/cracking (0.1 to 0.2). A weighted factor assigned to each injury criterion provided an overall total injury estimate of 0 to 100%. When applied at 1× rates, total injury for 2,4-D isooctyl ester was 10% for cotton and 36% for tomato and for triclopyr butoxyethyl ester was 11% for cotton and 50% for tomato. For the 2,4-D DMA, 2,4-D acid, dicamba DMA, dicamba DGA, dicamba acid, and triclopyr acid formulations, total injury was 4 to 8% for cotton and 20 to 24% for tomato, and for both crops, injury was no greater than for the nontreated.

Pale Swallowwort (Vincetoxicum rossicum) Response to Cutting and Herbicides

AbstractEffective control techniques for pale swallowwort (PSW), an invasive herbaceous vine of old fields and forest understories, are limited. We conducted a 3-yr cutting and herbicide study on an adjacent old-field and forest understory site near Ithaca, NY, for control of PSW. Plants in experimental plots were cut in early July and cut again or sprayed in late August for two seasons with the isopropylamine salt of glyphosate, or one of two rates (low or high) of either triclopyr triethylamine salt (i.e., SL, SH) or triclopyr butoxyethyl ester (EL, EH). The herbicide treatments were effective in reducing PSW cover, plant (stem) density, and aboveground biomass in the old-field site, but in several cases, only after 2 yr of cutting plus herbicide application. Only the cutting plus SH treatment did not reduce PSW cover relative to the unmanaged control in the forest understory and no treatment reduced biomass. In general, the cutting plus EH treatment was most effective in reducing PSW stem densities in the forest site. The most effective herbicide treatments differed between sites. Cutting plus EH reduced PSW cover by 84% and stem density (> 5 cm) by 86% in the old-field site. Cutting plus SH effectively decreased long and short (≤ 5 cm) stem densities by 86 and 96%, respectively. Cutting plants twice during each of two seasons increased PSW cover by 301% and density of stems > 5 cm by 73% at this site. In the forest site, cutting plus glyphosate, or cutting plus EH or cutting plus SL and EL resulted in the greatest reductions in PSW cover (80, 76, 66, and 56%, respectively). Cover in plots cut twice per year decreased by 19%. The EH or SL treatments decreased long-stem densities by 78 and 71%, respectively. The EH treatment decreased short-stem density by 37%. These findings suggest that integrated techniques may control PSW but that effective management strategies may be habitat constrained.

Study on Properties of Inclusion Complexation of Triclopyr Butoxy Ethyl Ester with Mixed Surfactant System

β‐cyclodextrin exhibits the property of forming inclusion complexes with various molecules. These complexes display improved properties in comparison with starting molecules in terms of their solubility and stability. In the present study, triclopyr butoxy ethyl ester, a selective systemic herbicide was utilized for forming inclusion complexes with β‐cyclodextrin in absence and presence of the nonionic: lauric acid monoethanolamide (C12MEA)/anionic: α‐olefin sulfonate (AOS) mixed surfactant system. The objective of present work was to study the important physical properties like dissolution rate, dispersion stability and wettability in presence of mixed surfactant systems of inclusion complex of a herbicide. Coprecipitation method was used for inclusion complex formation, which was consequently characterized by analytical techniques such as x‐ray diffractometry (XRD), differential scanning calorimetry (DSC) and ultra‐violet spectroscopy (UV).

Developmental toxicity evaluation of triclopyr butoxyethyl ester and triclopyr triethylamine salt in the CD rat

Triclopyr (3,5,6-trichloro-2-pyridyloxyacetic acid) is an herbicide used extensively in the control of woody plants and broadleaf weeds, and is often formulated as a triethylamine salt (T-TEA) or butoxyethyl ester (T-BEE). This study evaluated the developmental toxicity of T-TEA or T-BEE in time-mated CD rats gavaged on gestation days 6–15 with 0, 30, 100 or 300 mg/kg body weight (bw)/day. The doses of each compound were equimolar and equivalent to 22, 76, 216 mg/kg bw/day of triclopyr, based on prior studies indicating rapid cleavage of the salt or ester and equivalent pharmacokinetics for the active ingredient. T-TEA caused maternal toxicity, evidenced by the death of one high-dose dam, reduced body weight gain, increased relative liver and kidney weights (300 mg/kg bw/day), reduced feed consumption, and increased water consumption (100 and 300 mg/kg bw/day). Developmental effects were limited to slightly decreased fetal body weight and reduced skeletal ossification at the high dose level. T-BEE caused similar, albeit slightly more severe, maternal toxicity, with three maternal deaths at 300 mg/kg bw/day, and slight maternal effects at 30 mg/kg bw/day. Due to an equivocal increase in malformations, which were mainly clustered in litters from three high dose dams with marked maternal toxicity, the T-BEE study was repeated using 30 dams/group, investigator-blind fetal evaluations, and an additional dose group (5 mg/kg bw/day). In the repeat study, the only reproducible fetal effect was an increased incidence of 14th thoracolumbar rib at 300 mg/kg bw/day. Overall analysis of the two T-BEE studies suggested that the fetal malformations unique to the initial study likely reflected a combination of spontaneous events, exacerbated by marked maternal toxicity. The combined weight of evidence from these developmental toxicity studies, coupled with their known pharmacokinetic equivalence, indicates that T-BEE and T-TEA are not selectively toxic to the fetus. The respective maternal toxicity no-observed effect levels (NOEL) for T-BEE and T-TEA were 5 and 30 mg/kg bw/day, while the NOEL for developmental toxicity was 100 mg/kg bw/day for both compounds.

Complexation of Triclopyr Butoxy Ethyl Ester with β‐Cyclodextrin

β‐cyclodextrin (β‐CD), a macro‐cyclic oligosaccharide exhibits the property of forming inclusion complexes with various molecules. These complexes display some improved properties of starting molecule such as, increase of aqueous solubility, improvement in stability as well as reduction of bad odor and/or toxicity of molecules. The formulation of an inclusion complex of β‐CD as the host molecule and triclopyr butoxy ethyl ester, a selective systemic herbicide, as guest molecule has been studied as an initial step towards the improvement in the conventional herbicide formulations. The interaction of triclopyr butoxy ethyl ester with β‐CD produced the formation of an inclusion complex. Three processing methods (kneading, co‐precipitation and co‐evaporation) were used to prepare solid inclusion complexes. X‐ray diffraction (XRD), differential scanning calorimetry (DSC) and ultra‐violet (UV) spectroscopy techniques were used to study the complexation of this herbicide. The objective of the present work was to study the complexation and enhanced aqueous solubility of triclopyr butoxy ethyl ester. Phase solubility study suggested the existence of a 1:1 complex between herbicide and β‐CD. XRD and DSC analysis indicated the existence of an inclusion complex of herbicide with β‐CD. Dissolution rate study was conducted so as to study dissolution properties of complexes. The dissolution rate of the complexed herbicide in aqueous media was considerably improved as compared with the uncomplexed herbicide. The study also attempts to compare the various methods of complex formation. The best results were obtained when inclusion complexes were prepared by co‐precipitation method. Findings of this paper will allow more rational applications of herbicide with increase in its efficiency.

Effect of release® herbicide on mortality, avoidance response, and growth of amphibian larvae in two forest wetlands

Effects of Release herbicide (triclopyr butoxyethyl ester, [TBEE]) on mortality, avoidance response, and growth of larval amphibians (Rana clamitans, Rana pipiens) were investigated using in situ enclosures deployed in two forest wetlands in northern Ontario, Canada. Release was applied at nominal concentrations ranging from 0.26 to 7.68 mg TBEE acid equivalents (AE)/L. No significant deleterious effects of this herbicide on larval growth were detected. However, concentration-dependent mortality and abnormal avoidance response were observed. Most mortality occurred within 96 h following treatment. Median lethal concentration (LC50) values for each species and experimental site ranged from 2.79 to 3.29 mg AE/L, while median effective concentration (EC50) values (abnormal avoidance response) ranged from 1.67 to 3.84 mg AE/L. The LC10 and EC10 endpoints approximated aqueous concentrations (0.59 mg AE/L) expected under direct aerial overspray scenarios, indicating a potential risk of impacts for a small proportion of native amphibian larvae. However, given the low frequency and limited use of this herbicide formulation in Canadian forestry, these risks are considered negligible. Changes in usage patterns would require concurrent chemical and biological monitoring of operational spray programs to accurately quantify the probability and magnitude of real-world exposures and to relate these exposure levels to concentration-response relationships including those described in this study.

Determining Exposure to Auxin-Like Herbicides. II. Practical Application to Quantify Volatility

Volatility and drift are problems commonly associated with auxin-like herbicides. Field and greenhouse studies were conducted at Texas A & M University to develop a method of quantifying volatility and subsequent off-target movement of 2,4-D, dicamba, and triclopyr. Rate–response curves were established by applying reduced rates ranging from 4 × 10−1to 1 × 10−5times the normal use rates of the herbicides to cotton and soybean and recording injury for 14 d after treatment (DAT) using a rating scale designed to quantify auxin-like herbicide injury. Injury from herbicide volatility was then produced on additional cotton and soybean plants through exposure to vapors of the dimethylamine salt of 2,4-D, diglycolamine salt of dicamba, and butoxyethyl ester of triclopyr using air chambers inside a greenhouse and volatility plots in the field. Injury resulting from this exposure was evaluated for 14 d using the same injury-evaluation scale that was used to produce the rate–response curves. Volatility-injury data were then applied to the rate–response curves so that herbicide rates corresponding with observed injury could be calculated. Using this method, herbicide volatility rates estimated from greenhouse-cotton injury were determined to be 3.0 × 10−3, 1.0 × 10−3, and 4.9 × 10−2times the use rates of 2,4-D, dicamba, and triclopyr, respectively. Greenhouse-grown soybean developed injury consistent with 1.4 × 10−2, 1.0 × 10−3, and 2.5 × 10−2times the normal use rate of 2,4-D, dicamba, and triclopyr, respectively. Under field conditions, cotton developed injury symptoms that were consistent with 4.0 × 10−3, 2.0 × 10−3, and 1.25 × 10−1times the recommended use rates of 2,4-D, dicamba, and triclopyr, respectively. Field soybean displayed injury symptomology concordant with 1.6 × 10−1, 1.0 × 10−2, and 1.1 × 10−1times the normal use rates of 2,4-D, dicamba, and triclopyr, respectively. This procedure provided herbicide volatility rate estimates that were consistent with rates and injury from the rate–response injury curves. Additional research is needed to ascertain its usefulness in determining long-term effects of drift injury on crop variables such as yield.

Toxicity of glyphosate and triclopyr using the frog embryo teratogenesis assay—Xenopus

AbstractThe effects of glyphosate ([N‐phosphonomethyl]glycine) and triclopyr ([[3,5,6‐trichloro‐2‐pyridinyl]oxy]acetic acid) on the embryonic development of Xenopus laevis were evaluated using Frog Embryo Teratogenesis Assay—Xenopus (FETAX). Rodeo®, the isopropylamine (ipa) salt of glyphosate formulated without a surfactant was found to be the least toxic, with a LC5 and LC50 of 3,779 and 5,407 mg acid equivalent (AE)/L, respectively. The LC5 and LC50 of Roundup®, the ipa salt of glyphosate formulated with a surfactant, was 6.4 and 9.4 mg AE/L, respectively. The surfactant component of Roundup, polyoxyethyleneamine (POEA), had a LC5 and LC50 of 2.2 and 2.7 mg/L, respectively. Garlon® 3A, the triethylamine salt of triclopyr, had a LC5 and LC50 of 119 and 162.5 mg AE/L, respectively. The LC5 and LC50 of Garlon 4®, the butoxyethyl ester of triclopyr, was 6.7 and 9.3 mg AE/L, respectively. Considering a theoretical worst case scenario when the highest rates recommended for glyphosate (12 L of Roundup/ha) or triclopyr (8 L of Garlon/ha) are applied to water 15 cm in depth, the expected environmental concentrations calculated on the basis of AE would be 2.8 and 2.6 mg AE/L, respectively. The margins of safety (LC5/expected environmental concentrations) for frog embryos exposed to these concentrations would be approximately 2, 2, 47, and 1,312 for Roundup, Garlon 4, Garlon 3A, and Rodeo, respectively.

Accumulation Dynamics of Triclopyr Ester in Aquatic Leaf Packs and Effects on Detritivorous Insects

AbstractPrevious field studies have demonstrated that residues of the herbicide, triclopyr butoxyethyl ester (3,5,6‐trichloro‐2‐pyridinyloxyacetic acid, butoxyethyl ester) (TBEE), can accumulate in submerged leaf material of aquatic systems at concentrations up to 20 times the maximum aqueous concentrations. Accumulated TBEE residues may pose a risk of adverse effects to detritivorous invertebrates inhabiting and using natural leaf packs. We examined the dynamics of TBEE accumulation and persistence in leaf materials of laboratory and outdoor aquatic systems, and determined the ecological significance of this in terms of effects on detritivorous insects and organic matter processing. Accumulations of TBEE in leaf packs of semi‐static laboratory microcosms were up to 80 times aqueous concentrations, and residues persisted for 4 to 5 d. Leaf material of flow‐through laboratory microcosms accumulated TBEE at much higher rates (up to 1000 times aqueous concentrations), but residues were cleared by 48 to 72 h. Accumulation and persistence in flow‐through units were dependent on water depth, velocity, and exposure duration. Accumulated TBEE residues were less in outdoor stream channels than in laboratory flow‐through units, probably because of losses through sorption to natural benthic material in the stream channels. Despite accumulations of TBEE in leaf packs at up to 90 mg kg−1 in systems treated at or near expected environmental concentrations, there was no significant mortality of detritivorous insects and no significant reductions in leaf consumption. Significant mortality and reduced feeding occurred only in systems treated at concentrations well above (up to 10 times) expected environmental concentrations.

Effect of Hand Defoliation on Herbicide Efficacy in Honey Mesquite

Greenhouse and field experiments were conducted to evaluate the effect of hand defoliation of honey mesquite (Prosopis glandulosa Torr) before herbicide application on herbicide efficacy. In the greenhouse, the monoethanolamine salt of clopyralid, the butoxyethyl ester of triclopyr, and 1:1 mixtures of clopyralid plus triclopyr were applied as foliar sprays at 140 g ha-1 each on 2-year-old single-stemmed plants averaging 50 cm tall. In the field, the same herbicides were applied as broadcast sprays at rates of 280 g ha-1 on multistemmed trees 1 to 2 m tall. Plants were defoliated prior to herbicide application at 0, 25, and 50% of original foliage. Defoliation at 25 or 50% did not reduce herbicide efficacy compared to nondefoliated plants in the greenhouse or field. The clopyralid:triclopyr mixture was sometimes synergistic in controlling honey mesquite in the greenhouse and field.