Search

Eucalyptus species are grown for fiber, fuel, and other uses on more than 17.8 million ha worldwide, yet some species are considered invasive and may have adverse environmental or social impacts outside their native range. Aminocyclopyrachlor (AMCP) and standard applications of imazapyr and triclopyr herbicides were compared for eucalyptus control using a basal stem application method. At 6 and 12 mo after treatment (MAT), basal stem applications using 5% (vol/vol) AMCP (120 g ae L−1) in methylated soybean oil (MSO) resulted in 97% to 99% eucalyptus crown reduction and generally provided greater control across all diameter classes than standard treatments of 28% imazapyr (240 g ae L−1) or 75% triclopyr ester (480 g ae L−1). AMCP at 5% was as effective as 40% vol/vol. Increases in stem live height at 24 MAT suggest that the effect of triclopyr ester basal stem treatment may be impermanent. AMCP treated trees did not have regrowth by 24 MAT.

Brazilian peppertree (Schinus terebinthifoliaRaddi) is an invasive shrub that is problematic in both freshwater wetlands and brackish mangrove communities. The complex structure, geographic remoteness, and general herbicide sensitivity of mangrove systems have resulted in great technical challenges for managers attempting selectiveS. terebinthifoliacontrol. Recent advances in auxin herbicide technologies warrant herbicide screening to address this growing problem. Therefore, greenhouse experiments were conducted in 2018 and 2019 to evaluate four non-target mangrove species andS. terebinthifoliaresponse to the three herbicides: aminocyclopyrachlor, aminopyralid, and florpyrauxifen-benyzl. Aminocyclopyrachlor controlledS. terebinthifolia, but was highly injurious to black mangrove [Avicennia germinans(L.) L.], red mangrove (Rhizophora mangleL.), white mangrove [Laguncularia racemosa(L.) C.F. Gaertn.], and buttonwood mangrove (Conocarpus erectusL.). Aminopyralid also controlledS. terebinthifoliabut its impact varied across mangrove species.Laguncularia racemosaandC. erectuswere highly sensitive to aminopyralid,R. mangleexhibited dose-dependent tolerance, andA. germinanswas highly tolerant. Florpyrauxifen-benzyl failed to controlS. terebinthifoliaand resulted in severe injury to all four mangrove species. These results indicate differential responses to newer auxins in both the target response and non-target plant community of interest. The efficacy of aminopyralid onS. terebinthifolia, coupled with its selectivity onA. germinanswarrants further testing.

The pesticide behavior in soils can be easily affected by biochar addition. However, studies on the effects of raw feedstock and biochar are scarce. The objective of this study was to evaluate the effect of amending soils from three Midwestern U.S. states, with biochar produced from soybean residues, sugarcane bagasse, and wood chips (grape) as well as raw feedstock on the sorption–desorption and leaching potential of the pesticides aminocyclopyrachlor, metolachlor, and imidacloprid. Soil was amended at 10% (w w−1), and sorption–desorption studies were performed using the batch equilibration method. Following the determination of the sorption coefficient (Koc) values, the groundwater ubiquity score (GUS) indices for these pesticides were calculated. The highest pesticide sorption in all unamended soils followed the order imidacloprid (Kd = 0.79–1.66 L Kg−1) > metolachlor (Kd = 0.54–0.61 L Kg−1) > aminocyclopyrachlor (Kd = 0.12–0.23 L Kg−1). Biochar has the potential to decrease metolachlor and imidacloprid availability in soil through increased sorption, while the availability of aminocyclopyrachlor differed between the use of raw feedstock and biochar. Biochar derived from wood chips had the highest impact on pesticide behavior. We confirmed that aminocyclopyrachlor, metolachlor, and imidacloprid would leach easily in the three unamended soils, as illustrated by the GUS index.

The pyridine carboxylic acid (PCA) herbicide family can exhibit differential activity within and among plant species, despite molecular resemblances. Aminocyclopyrachlor (AMCP), a pyrimidine carboxylic acid, is a recently discovered compound with similar use patterns to those of the PCA family; however, relative activity among PCAs and AMCP is not well understood. Therefore, the objective of this study was to quantify relative activity among aminopyralid, picloram, clopyralid, triclopyr, and AMCP in canola, squash, and okra using dose-response whole-plant bioassays. Clopyralid was less active than all other herbicides in all species and did not fit dose-response models. Aminopyralid and picloram performed similarly in squash (ED50= 21.1 and 23.3 g ae ha−1, respectively). Aminopyralid was 3.8 times and 1.7 times more active than picloram in canola (ED50= 60.3 and 227.7 g ha−1, respectively) and okra (ED50= 10.3 and 17.3 g ha−1, respectively). Triclopyr (ED50= 37.3 g ha−1) was more active than AMCP (ED50= 112.9 g ha−1) and picloram in canola. Aminocyclopyrachlor (ED50= 6.6 g ha−1) and triclopyr (ED50= 7.8 g ha−1) were more active in squash than aminopyralid and picloram. In okra, AMCP (ED50= 14.6 g ha−1) and aminopyralid (ED50= 10.3 g ha−1) performed similarly but were more active than triclopyr (ED50= 88.2 g ha−1). Herbicidal activity among AMCP and PCAs was vastly different despite molecular similarities that could be due to variable target-site sensitivity among species.

Aminocyclopyrachlor is a persistent herbicide in soil; in the presence of organic matter, this persistence can be increased and can contribute to environmental contamination. The objective of this study was to verify the effects of organic materials derived from the sugarcane cultivation system on the mineralization and degradation of aminocyclopyrachlor in the soil. 14C-aminocyclopyrachlor was applied to soil with organic residues (sugarcane straw, filter cake and vinasse) and evaluated for 112 days of incubation. Mineralization was quantified by the weekly evolution of 14CO2, and the extracted, bound residues and the formation of metabolites of aminocyclopyrachlor were quantified. The mineralization was lower than 45% in all treatments. The degradation half-life (DT50) is being 187 days for unamended soil and > 240 days for soils amended with organic materials. For 90% of the herbicide to be degraded (DT90), between 622 and 921 days was required in all soils. Bound residues were formed in the soil (30% of the total applied in all treatments). No metabolites were formed during the whole incubation period, regardless of the treatment. The presence of organic materials in the soil increased the persistence of aminocyclopyrachlor in the soil, so that persistence of the herbicide may promote a residual effect on weeds and carryover in subsequent crops.

Herbicides have been a primary means of managing undesirable brush on grazing lands across the southwestern United States for decades. Continued encroachment of honey mesquite and huisache on grazing lands warrants evaluation of treatment life and economics of current and experimental treatments. Treatment life is defined as the time between treatment application and when canopy cover of undesirable brush returns to a competitive level with native forage grasses (i.e., 25% canopy cover for mesquite and 30% canopy cover for huisache). Treatment life of industry-standard herbicides was compared with that of aminocyclopyrachlor plus triclopyr amine (ACP+T) from 10 broadcast-applied honey mesquite and five broadcast-applied huisache trials established from 2007 through 2013 across Texas. On average, the treatment life of industry standard treatments (IST) for huisache was 3 yr. In comparison, huisache canopy cover was only 2.5% in plots treated with ACP+T 3 yr after treatment. The average treatment life of IST for honey mesquite was 8.6 yr, whereas plots treated with ACP+T had just 2% mesquite canopy cover at that time. Improved treatment life of ACP+T compared with IST life was due to higher mortality resulting in more consistent brush canopy reduction. The net present values (NPVs) of ACP+T and IST for both huisache and mesquite were similar until the treatment life of the IST application was reached (3 yr for huisache and 8.6 yr for honey mesquite). At that point, NPVs of the programs diverged as a result of brush competition with desirable forage grasses and additional input costs associated with theoretical follow-up IST necessary to maintain optimum livestock forage production. The ACP+T treatments did not warrant a sequential application over the 12-yr analysis for huisache or 20-yr analysis for honey mesquite that this research covered. These results indicate ACP+T provides cost-effective, long-term control of honey mesquite and huisache.

Total vegetation control (TVC) is an essential management practice to eliminate all vegetation for the purpose of protecting infrastructure, people, or natural resources on sites where vegetation poses major fire, visibility, and infrastructure risks. TVC is implemented on sites such as railroads, power substations, airports, roadsides, and oil and gas facilities. Current research has identified that tank-mixing two effective mechanisms of action is a superior resistance management strategy compared to rotating mechanisms of action; however, effective tank mixes for TVC have not been thoroughly evaluated. A field experiment was conducted from 2013 to 2014 at five sites in Colorado to compare 32 treatment combinations to two industry standards for TVC. Research objectives were (1) to identify herbicide tank-mix combinations for TVC with multiple effective mechanisms of action for resistance management, (2) to evaluate lower use rate alternatives to minimize nontarget impacts, and (3) to determine the efficacy of fall versus spring application timings. Seven treatments were identified as top-ranking treatments, averaging 96% bare-ground (BG) across five sites and two application timings. Four out of the seven top-ranked treatments included aminocyclopyrachlor, chlorsulfuron, and indaziflam. The industry standard diuron plus imazapyr was in the top ranking, whereas the other industry standard bromacil plus diuron performed inconsistently across sites. Probability modeling was used to predict the probability of achieving 97% or 100% BG with various treatment combinations. The combination of aminocyclopyrachlor, chlorsulfuron, indaziflam, and imazapyr had the highest predicted BG probability, with 88% predicted probability of achieving 100% BG, compared to 67% and 52% predicted probabilities for the industry standards diuron plus imazapyr and bromacil plus diuron, respectively. In three of the five sites, fall applications outperformed the same treatments applied in the spring. Several top-ranking treatments represent newer, lower use rate herbicide combinations that provide multiple mechanisms of action to manage herbicide-resistant weeds and minimize nontarget impacts. Nomenclature: Aminocyclopyrachlor; bromacil; chlorsulfuron; diuron; imazapyr; indaziflam

Vegetable producers are often concerned about potential herbicide carryover and injury to vegetables following the application of livestock manure/compost from animals fed with treated hay. A greenhouse study was conducted to evaluate the effect of activated charcoal on soil residual activity of the herbicides aminopyralid, aminocyclopyrachlor, and picloram, applied at recommended field rates of 120 g ae, 70 g ai, and 303 g ai ha−1 respectively, on tomato, okra, and cantaloupe. A commercial source of activated charcoal was used at four rates [0, 0.5X, 1X, and 2X (1X = 336 kg ha−1)]. When no activated charcoal was applied, aminopyralid caused the greatest injury to tomato and okra, leading to plant death at 4 weeks after emergence/transplanting (WAE/T). At the highest rate (2X) of activated charcoal, crop injuries due to aminopyralid were reduced by 72 and 78% for okra and cantaloupe, respectively at 4 WAE, while tomato did not respond to the 2X rate of activated charcoal. For aminocyclopyrachlor, even a much lower rate (0.5X) of activated charcoal was sufficient to reduce about 70% of the injury caused on cantaloupe and okra. For picloram, activated charcoal application at the 2X rate reduced injury by 78–94% across the three vegetable species investigated. Under low herbicide residue levels that usually occur under carryover situations, a much lower rate of activated charcoal (

Minimizing the negative ecological impacts of exotic plant invasions is one goal of land management. Using selective herbicides is one strategy to achieve this goal; however, the unintended consequences of this strategy are not always fully understood. The recently introduced herbicide indaziflam has a mode of action not previously used in non-crop weed management. Thus, there is limited information about the impacts of this active ingredient when applied alone or in combination with other non-crop herbicides. The objective of this research was to evaluate native species tolerance to indaziflam and imazapic applied alone and with other broadleaf herbicides. Replicated field plots were established at two locations in Colorado with a diverse mix of native forbs and grasses. Species richness and abundance were compared between the nontreated control plots and plots where indaziflam and imazapic were applied alone and in combination with picloram and aminocyclopyrachlor. Species richness and abundance did not decrease when indaziflam or imazapic were applied alone; however, species abundance was reduced by treatments containing picloram and aminocyclopyrachlor. Species richness was only impacted at one site 1 yr after treatment (YAT) by these broadleaf herbicides. Decreases in abundance were mainly due to reductions in forbs that resulted in a corresponding increase in grass cover. Our data suggest that indaziflam will control downy brome (Bromus tectorumL.) for multiple years without reduction in perennial species richness or abundance. IfB. tectorumis present with perennial broadleaf weeds requiring the addition of herbicides like picloram or aminocyclopyrachlor, forb abundance could be reduced, and in some cases there could be a temporary reduction in perennial species richness.

Skunk-vine (Paederia foetidaL.) is an invasive vine native to eastern and southern Asia and is widely distributed in Florida, Hawaii, and other southeastern U.S. states; however, little research has focused on herbicide control. Greenhouse and field experiments were conducted to determine efficacy of aminocyclopyrachlor, aminopyralid, fluroxypyr, glyphosate, imazapic, triclopyr amine, and triclopyr ester at low and high labeled rates when foliar applied toP. foetidaat various growth stages in greenhouse experiments. Longer-term control was evaluated in field experiments in central Florida using the same herbicides. PRE herbicides labeled for use in landscape plantings, including dimethenamid-P, flumioxazin, indaziflam, isoxaben, and prodiamine, were also evaluated in greenhouse trials by seeding containers withP. foetidaseed. In greenhouse experiments, POST herbicides, including aminocyclopyrachlor, aminopyralid, glyphosate, both triclopyr formulations, and the high rate of fluroxypyr (0.24 kg ae ha−1), provided >90% control across all growth stages at 4 mo after treatment with no regrowth observed. Imazapic provided 49% to 89% control, with efficacy decreasing withP. foetidasize, and generally provided less control than other treatments. Field experiments confirmed results from greenhouse studies. In PRE trials, flumioxazin and prodiamine provided better control than all other PRE herbicides evaluated, reducing shoot weights by 99% and 84%, respectively, compared with nontreated controls. Our data suggest all herbicides evaluated POST could potentially be used to manageP. foetida, although less control was achieved with imazapic compared with other herbicides. Further research is needed to determine herbicide efficacy on more mature plants and to develop application methods that would be less injurious to non-target vegetation. In landscapes, flumioxazin or prodiamine could be used for PRE control, but POST options that are labeled for landscape use should be identified in future research.

The application of sewage sludge (SS) in agriculture is a practice used worldwide, and it is commonly applied in sugarcane to supply nutrients, with beneficial effects on crop productivity and soil; but SS can increase sorption and decrease desorption of herbicides. However, in tropical soils such as in Brazil, there are no studies regarding the behavior of pre-emergent herbicides, mainly aminocyclopyrachlor and mesotrione, in SS-amended soil. The aim of the present study was to determine the effect of municipal SS applied in agriculture on the sorption–desorption of aminocyclopyrachlor and mesotrione in clay soil. Aminocyclopyrachlor (pyrimidine-2-14C-aminocyclopyrachlor) and mesotrione (cyclohexane-2-14C-mesotrione) sorption–desorption was evaluated using a batch equilibrium method. Soil was amended at 0% (control – unamended), 0.1%, 1%, and 10% (w∙w–1) of air-dried SS corresponding to 1.2, 12, and 120 t∙ha–1. The Freundlich Kf sorption values of aminocyclopyrachlor and mesotrione were similar for all treatments, ranging from 1.07 to 1.45 and 3.48 to 4.25 µmol (1–1/n) L1/n∙kg–1, respectively. Overall, the lowest Kd sorption value of these herbicides was reported for SS-amended soil (1%), while in the SS-amended soil (10%) it was higher than unamended soil. The H value for aminocyclopyrachlor was ~1 (no hysteresis) and for mesotrione was on average 0.4 (hysteresis occurring). In conclusion, the present study indicates that SS applied in any crop to supply nutrients can slightly affect the sorption–desorption of aminocyclopyrachlor and mesotrione, but this small difference does not affect the bioavailability of these herbicides for weed control.

Cogongrass [Imperata cylindrica(L.) Beauv.] is an invasive grass in the southeastern United States, and its impacts strongly affect the region, especially Florida. Herbicide strategies have been limited to glyphosate in natural areas and imazapyr in managed pine forests and non-crop areas where its soil residual activity is of less concern. This lack of options has raised concern for herbicide resistance, which has never been documented forI. cylindrica. Land managers have also reported variableI. cylindricacontrol, especially with glyphosate. To determine whether herbicide resistance was a possible explanation, we examined glyphosate response ofI. cylindricafrom 12 Florida populations. We also tested aminocyclopyrachlor with and without glyphosate and flumioxazin with glyphosate. Results indicated that herbicide performance was similar acrossI. cylindricapopulations: glyphosate and aminocyclopyrachlor reducedI. cylindricabiomass by 78% and 76%, respectively, and the combined tank mix reduced cogongrass biomass by 91%. Flumioxazin tank mixed with glyphosate did not improve control compared with glyphosate alone. There were no differences in pretreatmentI. cylindricashoot height, with the exception of two panhandle populations that were shorter. Subsequent harvests indicated few differences in shoot and root plus rhizome weights among untreated controls for almost all populations, with the exception of one of the initially shorter panhandle populations. Our findings indicate that variability in glyphosate efficacy, as suggested by managers, is unlikely due to any conferred resistance. Other abiotic factors such as drought and shade and applicator factors such as carrier water quality should be examined to better understand this issue. Additional studies examining non-target impacts of aminocyclopyrachlor should be conducted to determine its potential fit intoI. cylindricamanagement.

Rush skeletonweed is emerging as a regionally important weed of winter wheat production in eastern Washington. Field studies were conducted during the 2016 and 2017 crop years to evaluate several auxin herbicides applied at two seasonal timings (fall or spring) for control of rush skeletonweed in winter wheat. Clopyralid (210 g ae ha-1) provided >90% visual control of rush skeletonweed in both years of the study and aminopyralid (10 g ae ha-1) provided >80% visual control. Aminocyclopyrachlor, dicamba, and 2,4-D provided

While previous studies have shown the influence of various biochars on the fate and transport of herbicides in soil, little information exists on the effects of bonechar. The aim of this research was to evaluate the effect of cow bonechar amendments on the sorption-desorption and leaching of aminocyclopyrachlor and mesotrione in a tropical soil. Soil was amended with bonechar at rates of 0 (control), 1, 5, 10, and 100% (pure bonechar) (w w− 1), corresponding to 0, 12, 60, 120, and 1200 t ha− 1, respectively. Additionally, two bonechar particle size groups were compared (0.3–0.6 and 0.15–0.3 mm). Aminocyclopyrachlor (pyrimidine-2-14C-aminocyclopyrachlor) and mesotrione (cyclohexane-2-14C-mesotrione) sorption-desorption was evaluated using the batch-equilibrium method and column leaching studies. Higher bonechar application rates increased the sorption of both herbicides. Aminocyclopyrachlor and mesotrione were leachable in the control soil, but the addition of bonechar reduced the depth at which both herbicides were detected. Bonechar additions to soil, regardless of the particle size, was able to statistically increase sorption, decrease desorption, and reduce the leaching potential of both herbicides in the soil.

Native forbs are an essential component in the functioning and diversity of prairie communities. Aminocyclopyrachlor (AMCP) will effectively control many noxious weeds that invade prairie communities; however, its efficacy on desirable broadleaf plants is relatively unknown. Few field studies have been reported, and locating adequate populations of native forbs for evaluation of tolerance to herbicides is difficult. The susceptibility of 10 prairie forb species to AMCP was evaluated in the greenhouse. Species were chosen to correlate with a field study of AMCP and a previous greenhouse experiment. AMCP was applied at 0, 35, 70, and 105 g ha−1 with a methylated seed oil (MSO) plus silicone-based non-ionic surfactant (NIS) blend at 0.25% v/v when plants reached the growth stage simulating a spring treatment for weed control. Blueflag iris (Iris versicolor L.) and harebell (Campanula rotundifolia L.) were relatively tolerant and would likely be unharmed following an application of AMCP in the field. Wild licorice (Glycyrrhiza lepidota Pursh), prairie wild rose (Rosa arkansana Porter), purple prairie clover (Dalea purpurea Vent.), and wild bergamot (Monarda fistulosa L.) were moderately susceptible to AMCP; however, plants might regrow in the field, since some survived at the highest AMCP application rate (105 g ha−1) evaluated. Skyblue aster [Symphyotrichum oolentangiense (Riddell) G. L. Nesom], Canada goldenrod (Solidago canadensis L.), blue cardinal-flower (Lobelia siphilitica L.), and blacksamson echinacea (Echinacea angustifolia DC.) were susceptible to AMCP even when applied at 35 g ha−1. The susceptibility of greenhouse-grown forbs to AMCP was the same or similar to species evaluated in the field and can be used to predict native forb tolerance in the field.

Aminocyclopyrachlor (AMCP) will control many invasive broadleaf weeds, but the susceptibility of desirable forbs is not widely known. Native prairie response to AMCP was evaluated near Fargo, ND, and Felton, MN, in the Northern Great Plains. Both sites had high floristic quality prior to treatment, with 33 and 80 different species at Fargo and Felton, respectively. AMCP was applied at 140 g ha−1 in July 2014 to coincide with leafy spurge and Canada thistle treatment timing. AMCP altered the plant communities and reduced foliar cover of undesirable species, high seral forbs (undisturbed stable communities), and low seral forbs (early succession in disturbed communities) at both locations at 10 and 14 mo after treatment (MAT). AMCP reduced Canada thistle and leafy spurge in Fargo and eliminated hedge bindweed, prickly lettuce, and black medic in Felton. High seral forb foliar cover was reduced at 10 and 14 MAT from 20% to 2% and 3% in Fargo and from 19% to 1.6% and 2% in Felton, respectively. The high seral forb species birdfoot violet, white panicled aster, northern bedstraw, Canada goldenrod, purple meadowrue, and American vetch were reduced at both locations. Low seral forb cover also decreased at 10 MAT from 22% to 10% in Fargo and from 12% to 1% in Felton, respectively. By 14 MAT, low seral species in Fargo recovered to 16%, but recovery was much slower in Felton and slightly increased to 1.5%. After treatment high and low seral monocot species increased at both sites, likely due to reduced competition from susceptible species. AMCP reduced richness, evenness, and diversity at both locations at 10 and 14 MAT; therefore, floristic quality declined. A decline in diversity is generally undesirable but could have beneficial effects if invasive weeds and other undesirable species are reduced or eliminated.

Legumes such as alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.) increase forage productivity and quality in northern temperate pastures, but require re-establishment following broadleaf weed control using herbicides. To quantify the residual effects of two herbicides (aminocyclopyrachlor and aminopyralid) on potential legume re-establishment we examined alfalfa and clover recruitment at two field sites over two years. Sites were over-seeded with alfalfa and clover to populate the seed bank, and then sprayed with herbicide, after which seedling densities were monitored in late summer and fall of the current growing season. Defoliation (via mowing) effects were also assessed to evaluate the role of vegetation competition on legume establishment. Herbicides were applied at recommended rates (1.0), and 0.5, 0.25, 0.125, 0.0625, and 0 times recommended field rates, emulating exponential herbicide degradation (one through four half-lives). Alfalfa and white clover seedling densities were negatively impacted by all rates of herbicide, with modestly greater negative impacts from aminopyralid than aminocyclopyrachlor, although responses to herbicides remained site and legume specific. Reductions in alfalfa and clover were particularly evident through the 0.25 (i.e., two half-life) herbicide rate, with reductions in alfalfa ranging from 78% to 95%, and in clover from 73% to 88%. Legume densities at the 0.125 (three half-life) rate were 39%&ndash, 68% lower than those in nonsprayed control plots. Our results suggest that at least three half-lives of degradation must occur, and likely four or more, before these legumes can re-establish at densities acceptable for pasture production. These findings have implications for producers seeking to promptly re-establish forage legumes within pastures sprayed for broadleaf weed control in northern temperate regions.

Woolly distaff thistle is a long-lived winter annual that threatens the ranching and dairy industries within the North Coast counties of California, particularly the organic producers. No peer-reviewed publications have documented effective control options or integrated management approaches for this species. We conducted two experiments, each replicated, in Marin County, California. The first compared several conventional herbicides at two timings and rates, while the second compared a conventional herbicide treatment with organic and integrated organic control methods, including an organic herbicide (mixture of capric and caprylic acids). Results of the conventional herbicide treatments showed most spring applications (March or April) of aminopyralid, aminocyclopyrachlor, clopyralid, and combinations of aminopyralid + triclopyr, or aminocyclopyrachlor + chlorsulfuron had greater than 99% control of woolly distaff thistle with fewer than 1.5 seedlings per 27-m2 plot by the end of the growing season. Higher rates were generally necessary to achieve the same level of control with winter (January) applications. In the organic herbicide treatments, the most consistent treatment was a combination of mowing followed by 9% (v/v) or the organic herbicide. This treatment was slightly less effective compared with aminopyralid but did have better than 95% control of woolly distaff thistle. The results of this study provide control options for both conventional and organic ranching practices where woolly distaff thistle is a problem.

There are an estimated 400 million hectares of non-cropland in the United States primarily designated as rangeland and pastureland, and there are more than 300 invasive weeds found on these sites, causing an estimated annual loss of $5 billion. Among the most invasive and problematic weeds are Dalmatian toadflax, diffuse knapweed, downy brome, and musk thistle. Currently, herbicides are the most common management strategy for broadleaf weeds and invasive winter annual grasses. Indaziflam, a new herbicide for invasive plant management in non-crop areas, is a cellulose-biosynthesis inhibitor capable of providing residual invasive winter annual grass control up to 3 yr after treatment (YAT). A field experiment was conducted to determine whether residual Dalmatian toadflax and downy brome control by aminocyclopyrachlor, imazapic, and picloram could be extended by tank mixing these herbicides with indaziflam. Indaziflam tank mixed with aminocyclopyrachlor, imazapic, and picloram provided increased Dalmatian toadflax (84% to 91%) and downy brome (89% to 94%) control 4 YAT, compared with treatments excluding indaziflam. Treatments without indaziflam controlled 50% to 68% of Dalmatian toadflax and

Two varieties of bahiagrass were evaluated under Florida conditions for forage tolerance to the new herbicide, aminocyclopyrachlor (ACP), which is essential for product development decisions. Herbicide treatments included ACP alone at 70 and 140 g ai ha−1, ACP + chlorsulfuron at 69 + 27 and 138 + 54 g ai ha−1, ACP + 2,4-D amine at 70 + 532 g ai ha−1 and 140 + 1,064 g ai ha−1, ACP + triclopyr-amine at 70 + 140 g ai ha−1 and 140 + 280 g ai ha−1, and ACP + metsulfuron at 46 + 7, 78 + 12, and 168 + 26 g ai ha−1, and also included a nontreated check. ‘Argentine’ bahiagrass was the most tolerant forage species, and ‘Pensacola’ bahiagrass was sensitive to ACP + metsulfuron and initially to ACP + chlorsulfuron. Herbicide applications using ACP, when labeled, will likely provide good to excellent control of several weed species, with little long-term impact on bahiagrass forage production when the cultivar is known.

Duncecap larkspur (Delphinium occidentale [Wats.] Wats.) is an important perennial weed on high-elevation rangelands because of significant cattle losses due to toxic alkaloids in the plant. Aminocyclopyrachlor was evaluated at six rates between 17.5 and 315 g ai · ha−1 for larkspur control alone, and in combination with chlorsulfuron or metsulfuron, at a high-elevation location in Wyoming. Aminocyclopyrachlor-containing treatments were compared with 1120 g ai · ha−1 picloram and 63 g ai · ha−1 metsulfuron-methyl. Herbicides were applied to two sites in a randomized complete block design with four replicates each on June 18, 2010 at the first site and June 28, 2011 at the second site. Larkspur mortality, plant species richness, vegetation cover, and grass biomass data were collected 1 yr after treatment. Cover data were used to calculate vegetation diversity and to assess changes in species composition associated with herbicide application. A four-parameter log-logistic model was used to evaluate larkspur mortality, species richness, and vegetation cover in response to aminocyclopyrachlor rate. Ninety-percent larkspur reduction was obtained with aminocyclopyrachlor applied alone at rates of 168−303 g ha−1, depending on site. Mixture of aminocyclopyrachlor plus chlorsulfuron at a 2.5:1 ratio required 102−127 g ha−1 of aminocyclopyrachlor to reduce larkspur 90%. Aminocyclopyrachlor plus metsulfuron was the most effective herbicide combination for larkspur control of those we evaluated, requiring 47 + 15 g ha−1, respectively, to reduce larkspur 90%. Species richness and diversity were reduced by herbicide rates required to effectively control larkspur. Graminoid biomass was not significantly impacted by herbicide or rate. Aminocyclopyrachlor may be a useful tool for duncecap larkspur control. Addition of chlorsulfuron or metsulfuron to aminocyclopyrachlor increased larkspur control but had a greater impact on associated nontarget vegetation.

Macartney rose is an aggressive, thorny shrub that suppresses forage production and strongly hinders cattle grazing in southern pastures. Previous studies have found this weed to be extremely difficult to control with most pasture herbicides. We conducted two studies in central Alabama to assess several new herbicide chemistries applied at spring, early fall, and late fall timings. In the first study, we compared aminocyclopyrachlor, tank mixed with either 2,4-D, triclopyr, metsulfuron, or chlorsulfuron, with the commercial standard, picloram + 2,4-D. In the second study, we compared aminopyralid, tank mixed with either 2,4-D or metsulfuron and triclopyr + fluroxypyr, to the commercial standard, picloram + 2,4-D. Aminocyclopyrachlor + chlorsulfuron or metsulfuron and aminopyralid + 2,4-D or metsulfuron provided acceptable control and were comparable to picloram + 2,4-D at the early fall timing. Macartney rose control with treatments applied at the late fall timing tended to be less than commercially acceptable levels. We found that no herbicide treatment controlled Macartney rose at the spring timing. In addition, triclopyr + fluroxypyr did not control Macartney rose at any application timing. These results indicate that the early fall timing was optimal and that both aminocyclopyrachlor and aminopyralid can provide good Macartney rose control when mixed with certain other herbicides, including metsulfuron.

When invasive weeds are removed with herbicides, revegetation of native species is often desirable. The extended soil activity of aminocyclopyrachlor is important for long-term weed control but could reduce recovery of native species as well. The effect of aminocyclopyrachlor applied alone or with chlorsulfuron on cool- and warm-season grass species commonly used for revegetation was evaluated. The cool-season grasses included green needlegrass, intermediate wheatgrass, and western wheatgrass, whereas the warm-season grasses were big bluestem, sideoats grama, and switchgrass. A separate experiment was conducted for each species. Aminocyclopyrachlor was applied at 91 to 329 g ha−1 alone or with chlorsulfuron from 42 to 133 g ha−1 approximately 30 d after emergence. Warm-season grasses generally were more tolerant of aminocyclopyrachlor than the cool-season grasses evaluated in this study. Switchgrass and big bluestem were the most tolerant of the warm-season species when aminocyclopyrachlor was applied at 168 g ha−1 and averaged 199 and 150% forage production, respectively, compared with the control. Green needlegrass was the most tolerant cool-season grass. Western wheatgrass was the least tolerant species evaluated because forage production only averaged 32% of the control the year after treatment and thus would not be suitable for seeding if aminocyclopyrachlor was applied. The effect of chlorsulfuron applied with aminocyclopyrachlor varied by grass species. For example, green needlegrass injury 8 wk after treatment (WAT) averaged 30 and 48% when aminocylopyrachlor was applied alone, respectively, but injury was reduced to less than 16% when aminocyclopyrachlor was applied with chlorsulfuron. However, injury on the less-tolerant intermediate wheatgrass ranged from 48 to 92% by 4 WAT when aminocyclopyrachlor was applied alone and from 60 to 86% when chlorsulfuron was included in the treatment.

Because horsenettle and tall ironweed are difficult to control in cool-season grass pastures, research was conducted in Tennessee and Kentucky in 2010 and 2011 to examine the efficacy of aminocyclopyrachlor on these weeds. Aminocyclopyrachlor was evaluated at 49 and 98 g ai ha−1alone and in mixtures with 2,4-D amine at 371 and 742 g ae ha−1. Aminopyralid was also included as a comparison treatment at 88 g ai ha−1. Treatments were applied at three POST timings to horsenettle and two POST timings to tall ironweed. By 1 yr after treatment (YAT) horsenettle was controlled 74% with aminocyclopyrachlor plus 2,4-D applied late POST (LPOST) at 98 + 742 g ha−1. By 1 YAT, tall ironweed was controlled ≥ 93% by aminocyclopyrachlor applied early POST (EPOST) or LPOST, at rates as low as 49 g ha−1. Similar control was achieved with aminopyralid applied LPOST. Both aminocyclopyrachlor and aminopyralid were found to reduce horsenettle and tall ironweed biomass the following year. Moreover, all LPOST applications of aminocyclopyrachlor alone or in mixtures with 2,4-D prevented regrowth of tall ironweed at 1 YAT. Based on these studies, a LPOST herbicide application in August or September when soil moisture is adequate is recommended for control of horsenettle and tall ironweed in cool-season grass pastures.

Members of the Convolvulaceae family are known to be sensitive to aminocyclopyrachlor, although little is known about the absorption, translocation and metabolism of the herbicide in these species of weed. The aim of this study was to evaluate the absorption, translocation and metabolism of ¹⁴C‐aminocyclopyrachlor in young plants of Ipomoea purpurea and Ipomoea triloba. Assessments were performed at 3, 6, 12, 24, 48 and 72 h after treatment (HAT) for the study of absorption and translocation. Metabolism was assessed at three time points (3, 24 and 72 HAT). In terms of absorption, was observed a difference between species at the 3 and 48 HAT time points, where I. purpurea had a higher absorption of ¹⁴C‐aminocyclopyrachlor. No differences were observed between species at any other time points. Of the total absorbed herbicide, 90.9% for I. purpurea and 91.8% for I. triloba were detected on the treated leaf. I. purpurea presented higher translocation to the leaf above the treated leaf, while I. triloba showed higher translocation to the lower leaves and roots. No increase in absorption of ¹⁴C‐aminocyclopyrachlor was observed above 24 HAT for I. purpurea and above 6 HAT for I. triloba, and translocation was low (

The straw on the soil in the green cane harvesting system acts as a physical barrier to the action of the pre-emergence herbicides. However, some herbicides have physico-chemical characteristics to pass through the straw in water solution. The aim was to evaluate the influence of different densities of sugarcane straw on the leaching of aminocyclopyrachlor in a tropical soil (Oxisol—Typic Hapludox) in a system of green cane harvesting. The experiment was carried out using glass columns filled with soil, with and without sugarcane straw (0, 5, 10, and 20 t ha−1) on the top of the soil. 14C-aminocyclopyrachlor was applied followed by 200 mm of simulated rain for 48 h. The herbicide was detected in all soil layers (0–30 cm), and in the leachate (> 30 cm), in small trace amounts (≤ 0.21%) in all treatments, showing that aminocyclopyrachlor undergoes a high degree of leaching in the clayey soil. In the absence of straw, 39% of the herbicide remained in the upper layer (0–5 cm). In the presence of straw, the herbicide was distributed through the soil profile, mainly from 0 to 25 cm. Forty percent more herbicide was retained in the straw with 20 t ha−1 of sugarcane straw. Thus, it is concluded that the straw in high amounts retains aminocyclopyrachlor, but does not prevent it from reaching the soil; the high solubility of the herbicide and intense rainfall in a short period of time are factors that contribute to the herbicide passing through this barrier.

Among the most important and visible weeds in the Southeastern USA is the exotic invasive vine, kudzu (Pueraria montana var. lobata). Efforts to eradicate it typically involve many years of application of restricted-use pesticides. Recent availability of effective, non-restricted-use pesticides and developments with the application of the bioherbicide Myrothecium verrucaria has made possible new control programmes for kudzu management. Field trials at three sites over two years with aminocyclopyrachlor, aminopyralid, fluroxypyr, metsulfuron methyl and combinations of these herbicides achieved 99–100% reduction in aboveground kudzu biomass. Additionally, programmes were developed that eradicated kudzu while simultaneously establishing native vegetation. One of these successful programmes integrated bioherbicide application, mechanical removal of kudzu biomass and planting switchgrass (Panicum virgatum) in an entirely chemical herbicide-free system. These field tests demonstrate a variety of methods...

Most tall fescue in the United States is infected with a fungal endophyte which imparts certain advantages to the plant, such as drought tolerance, insect feeding deterrence, and enhanced mineral uptake. However, the endophyte also produces ergot alkaloids that are harmful to livestock and contribute to fescue toxicosis. Because the alkaloids are concentrated in seed and stems, a potential way to reduce the likelihood of fescue toxicosis is by suppressing seedhead formation with herbicides. Research was conducted from 2012 to 2014 using metsulfuron applied alone and in combination with other herbicides in spring to determine the growth response of tall fescue, effects on forage quality, and ergot alkaloid concentration. Clipping or metsulfuron applied alone or in combination with aminocyclopyrachlor or aminopyralid reduced seedhead density by 36 to 55% compared to the nontreated control. Treatments containing metsulfuron reduced spring harvest yield 35 to 61%, but no differences were observed in the summer or year-after harvests. The same treatments increased crude protein levels by 1.03 to 2.14% and reduced acid detergent fiber levels by 1.60 to 2.76% compared to the nontreated control at spring harvest. Treatments containing metsulfuron reduced ergot alkaloid concentration 26 to 34% at the spring harvest, but no differences were observed in summer-harvested forage. Results from this study indicate metsulfuron applied alone or in combination with aminocyclopyrachlor or aminopyralid can potentially reduce the severity of fescue toxicosis and improve forage quality.

Aminocyclopyrachlor (AMCP) is a pyrimidine carboxylic acid herbicide that is being evaluated for weed control on highway right-of-ways. The goal of this study was to evaluate weed control capabilities and tolerance of desirable turf to AMCP. The objective of the weed efficacy trial was to determine if AMCP (66, 132, and 263 g ai ha−1) was as effective as aminopyralid (18, 53, and 88 g ai ha−1) for controlling two weed species, mat lippia andBidens alba. In 2011, AMCP applied at 132 g ai ha−1resulted in 93% control of mat lippia at 2 mo after treatment (MAT) and 65% control at 3 MAT. In 2012, AMCP at 66 or 132 g ha−1resulted in 93 to 97% control of mat lippia, respectively, at 3 MAT. Aminopyralid, applied POST, never exceed 10% control of mat lippia in 2011 and 60% control in 2012. AMCP, applied POST, at 66 g ha−1, controlled ofB. alba84%, similar to the 89% control seen with aminopyralid at 88 g ha−1. The level of control from AMCP of the two weed species was equal to or greater than aminopyralid. An additional objective was to determine the tolerance of common bermudagrass and ‘Pensacola' bahiagrass to AMCP (66, 132, and 263 g ai ha−1) and imazapic (35 and 70 g ai ha−1) applied alone and in combination. Applications were made in late spring during seedhead initiation. No additional chlorosis was detected when imazapic was applied in combination with AMCP for either turf species. Averaged across imazapic rates, AMCP at 66 and 132 g ha−1, within the suggested rate range (48.5–132 g ai ha−1), did not cause greater than 25% chlorosis at any time. Chlorosis observed for AMCP applied alone and in combination with imazapic was acceptable and decreased to zero by 8 to 10 wk after treatment.

Absorption and translocation of aminocyclopyrachlor (AMCP) was investigated in black walnut. Radiolabeled AMCP was applied foliarly as a free acid, and basally as a free-acid-formulated oil-soluble liquid and as a methyl ester emusifiable concentrate. Maximum absorption was 68% for the methyl ester, 47% for the free-acid oil-soluble liquid, and 8% for the free acid when evaluated as percent applied. When recovered AMCP was presented as Bq g−1, no difference was observed in AMCP absorption or translocation of 14C-labeled material out of treated plant parts. Recovery of applied radiolabeled material in the roots from basal applications was 5 to 11% 72 h after treatment (HAT), compared with 0.8% recovery from a foliar application. Regardless of chemical form or formulation type, comparable injury was observed within 72 HAT despite low levels of translocation. Nomenclature: Aminocyclopyrachlor; black walnut, Juglans nigra L.

Studies under Florida conditions for susceptibility of pasture weed species to the new herbicide, aminocyclopyrachlor (ACP), are essential. Sensitivity of weed species was dependent upon the species and environment. Whitehead broom was not susceptible to ACP. Dogfennel control was consistently above 85% 1 yr after treatment with ACP at 140 g ha−1 and all ACP premixes. Milkpea was initially sensitive to all ACP treatments, but regrowth was evident in all treatments after 1 yr at one location. All ACP treatments resulted in 100% control of tropical soda apple 1 yr after treatment at one location, but less than 50% control at a second location. Herbicide applications with ACP, when labeled, will likely provide good to excellent control (80 to 100%) of several weed species. Nomenclature: Aminocyclopyrachlor; chlorsulfuron; metsulfuron; triclopyr-amine; 2,4-D amine; dogfennel, Eupatorium capillifolium> (Lam.) Small; milkpea, Galactia sp. P. Br.; ragweed parthenium, Parthenium hysterophorus L.; tropical soda ap...

The pyrimidine herbicide aminocyclopyrachlor was evaluated for crop tolerance and weed control in wild blueberry (Vaccinium angustifolium Aiton). Preemergence applications of aminocyclopyrachlor at a rate of 50 g a.i. ha−1 did not reduce aboveground blueberry biomass, yield potential, or final yield, and this rate appears safe for use in wild blueberry. Preemergence applications of aminocyclopyrachlor at a rate of 100 g a.i. ha−1 reduced aboveground blueberry biomass, but yield potential and final yield were only reduced significantly at application rates of 200 and 400 g a.i. ha−1. Preemergence applications of aminocyclopyrachlor at a rate of 100 g a.i. ha−1 effectively suppressed Euthamia graminifolia (L.) Nutt., and further evaluation of aminocyclopyrachlor to identify safe application timings and rates in wild blueberry is warranted. Aminocyclopyrachlor applied as a directed spot spray provided good control of several herbaceous and woody perennial weeds, and this use pattern could provide an alternative management option for many perennial weeds in wild blueberry.

Chemical application is a viable and popular method for weed control, but the effectiveness of various herbicides depends on the target weed. The objectives of this study were to determine the appropriate herbicide for three tall fescue varieties that either do or do not contain endophytic fungi. Plants were split into six herbicide treatments and an untreated control for 7, 14, 21, and 28 days in a randomized complete block design experiment with four replicates. Herbicides evaluated were 2,4-D, aminopyralid, 2,4-D plus dicamba, metsulfuron plus chlorsulfuron, aminocyclopyrachlor, and metsulfuron plus aminopyralid. In all three tall fescue varieties, the application of 2,4-D, aminopyralid, 2,4-D plus dicamba, or aminocyclopyrachlor failed to reduce phytotoxicity, height, tiller number, and dry matter when compared with the untreated control. However, metsulfuron-containing treatments reduced all variables in every variety. We thus conclude that herbicides containing metsulfuron are the most phytotoxic to tall fescue. Key words: Endophytic fungi, grass, weed control.

Tall buttercup is an invasive forb that has been reported in all but eight states and one Canadian province. The species has been of concern in Montana where it has invaded over 8,300 ha, and it has been particularly problematic in irrigated hayfield meadows that are used for forage production. This study sought to develop an integrated management strategy to control tall buttercup while maintaining forage production. Research was conducted over 2 yr at flood-irrigated and subirrigated hayfield meadows near Twin Bridges, MT. Treatments were randomly applied in a split-plot design with four replications at both sites. Herbicide treatments occurred at the whole-plot level: nonsprayed, aminopyralid (172 g ai ha−1), aminocyclopyrachlor + chlorsulfuron (83 g ai ha−1+ 33 g ai ha−1), and dicamba (981 g ai ha−1). Split plots consisted of mowing and fertilization (28 kg N ha−1). All herbicides provided up to 2 yr of tall buttercup control at both sites. In the second year, aminocyclopyrachlor + chlorsulfuron and aminopyralid reduced tall buttercup by 93% and 96%, respectively, for the subirrigated and flood-irrigated sites. At the subirrigated site, mowing reduced tall buttercup by 71%, and fertilization reduced it by 57%. Forage decreased following aminocyclopyrachlor + chlorsulfuron treatments. The integration of herbicide, mowing, and fertilization did not improve tall buttercup control.

Yellow toadflax (Linaria vulgaris P. Mill.) infestations in North Dakota increased 300-fold from 1997 to 2011, when the plant was added to the state noxious weed list. Long-term control of other invasive species had included biological control agents, but no effective agents for yellow toadflax had been identified, so a control program using herbicides was needed. The objective was to shift from short-term control with picloram applied in the fall at maximum allowed rates to long-term management with minimal nontarget species impact with an adaptive management approach. Yellow toadflax control was increased from an average of 64% with picloram at 1,120 g ha−1 alone 12 mo after treatment (MAT) to over 90% when applied with diflufenzopyr while the picloram rate was reduced 50%. Yellow toadflax control with aminocyclopyrachlor applied at 140 g ha−1 ranged from 91 to 49% 12 MAT when applied in June or September, respectively. In contrast, yellow toadflax control with picloram plus dicamba plus diflufenzopyr averaged > 90% regardless of application date during the growing season. Land managers now have at least two options for long-term yellow toadflax control with a wide window of application timing. The goal of replacing a single high-use–rate herbicide treatment was met but both picloram and aminocyclopyrachlor can injure many desirable forbs. However, application timing can now be adjusted to have the least impact on nontarget species. The adaptive development program led to a 58% reduction in yellow toadflax infestations in North Dakota by 2014.

The Sheyenne National Grassland (SNG) is a native tall grass and mixed grass prairie located in southeastern North Dakota. Approximately half of the SNG has been invaded by leafy spurge (Euphorbia esulaL.) and control methods have been limited. Many herbicides cannot be utilized at the SNG due to sandy soils (> 80%) and shallow groundwater, nor can they be applied near the western prairie fringed orchid (Platanthera praeclaraSheviak and Bowles), a federally listed threatened plant found on the SNG. Quinclorac and aminocyclopyrachlor were considered for use on the SNG but potential to enter the groundwater was unclear. Movement of quinclorac and aminocyclopyrachlor was evaluated in 70 cm soil columns that simulated field conditions from five ecological sites. Quinclorac leached further following the heavy rainfall event of 15 cm in 48 h compared to the annual precipitation of 51 cm applied over 9 wk. Quinclorac leached approximately 45 cm into the soil profile averaged over all soil types and both precipitation events but never exceeded 65 cm regardless of soil type. Aminocyclopyrachlor leaching was greater than quinclorac and moved through all soil types into the leachate following both watering regimes. Desorption of both herbicides was incomplete. Approximately 10 and 32% of applied aminocyclopyrachlor and quinclorac, respectively, remained in the top 5 cm of soil regardless of soil type or watering regime. Quinclorac but not aminocyclopyrachlor was considered suitable for use at the SNG to control leafy spurge and has the added benefit of not harming the western prairie fringed orchid.

Chinese tallowtree is an invasive tree found throughout the southeastern United States and in California. Its negative effects can be seen in numerous natural and managed ecosystems, including bottomland hardwood forests, pastures, pine plantations, and along lakes, ponds, streams, and rivers. Despite its troublesome presence for many decades, relatively few effective control strategies are available. Root sprouting following management efforts is a major impediment to successful control. Studies were conducted in Alabama and Louisiana at three locations to test several herbicides for cut stump, basal bark, and foliar individual plant treatment (IPT) methods. Herbicide treatments included triclopyr amine and ester formulations, imazamox, aminopyralid, aminocyclopyrachlor, and fluroxypyr. Data were collected just before leaf senescence at one and two growing seasons after treatment and included Chinese tallowtree foliar cover, number of stump or root collar sprouts, and number of sprouts originating from lateral roots within a 1-m radius of each tree. For the cut stump and basal bark studies, most herbicide treatments prevented sprouting from the stump or root collar region better than they did from the lateral roots. Aminopyralid reduced total sprouting better than all other treatments in the cut stump study. The high rates of aminocyclopyrachlor and fluroxypyr resulted in the highest mortality in the basal bark study. Aminocyclopyrachlor reduced total sprouting better than all other herbicides in the foliar treatment study. Triclopyr amine and ester formulations, which are commercial standards, did not consistently control Chinese tallowtree across these IPT studies. These studies provide some promising treatments to increase the number of effective tools that can be used to manage Chinese tallowtree. Additional research is needed to address the prolific nature of lateral root sprouting following any of these treatment methods.

Growers have observed lack of control of ragweed parthenium with glyphosate at 0.84 kg ae ha−1 used for weed control in noncrop areas and fallow fields in the Everglades Agricultural Area (EAA) of South Florida. Therefore, studies were conducted to (1) confirm and characterize the level of glyphosate resistance in ragweed parthenium from the EAA, (2) determine if reduced absorption or translocation is the mechanism of resistance of ragweed parthenium to glyphosate, and (3) evaluate the efficacy of POST herbicides commonly used in cultivated and noncrop areas for broadleaf weed control on flowering ragweed parthenium at the full and half labeled rate. A dose-response bioassay was used to determine the response of the rosette ragweed parthenium biotype from the EAA (resistant) and a susceptible biotype from Stoneville, MS, to glyphosate. The bioassay showed that the resistant biotype was 40- to 43-fold less sensitive to glyphosate when compared to the susceptible biotype. There was no significant difference in glyphosate absorption or translocation from the treated leaf to the rest of the plant 168 h after treatment between resistant and susceptible biotypes. This shows that absorption or translocation is not a mechanism of glyphosate resistance by ragweed parthenium. Saflufenacil + dimethenamid-P and hexazinone provided rapid and complete control of flowering ragweed parthenium 3 wk after treatment (WAT). Aminocyclopyrachlor + chlorsulfuron and aminopyralid at the full and the half label rates provided 100% control of ragweed parthenium by 9 WAT. Clopyralid, 2,4-D amine, and glufosinate at the full label rate provided 89 to 98% control of ragweed parthenium 9 WAT. Control of ragweed parthenium 9 WAT was < 75% with flumioxazin, fomesafen, glyphosate, imazapic, imazethapyr, mesotrione, oxyfluorfen, and paraquat, irrespective of use rate.

Choosing appropriate plant materials for restoration projects can affect establishment and persistence of desirable species. In situations where herbicides are used to manage invasive weeds, plant materials able to tolerate herbicides at early growth stages could increase probability of successful restoration of vegetation. However, little is documented regarding relative herbicide tolerance of native species commonly used in restoration and information regarding intraspecific variation for such characteristics is missing. We conducted a greenhouse study in 2010 and repeated in 2011 to investigate seedling response of 17 desirable species (27 germplasm), Russian thistle, and downy brome to aminocyclopyrachlor, a relatively new herbicide with potential applications in reclamation and restoration. We applied aminocyclopyrachlor at six rates between 10 and 320 g ha–1 30 days after planting. Grasses were in the three to five leaf stage and forbs and shrubs were less than five cm tall at the time of herbicide application. We used a log-logistic model to estimate dry weight reduction in response to aminocyclopyrachlor rate. Russian thistle biomass was reduced 95% at 120 g ha–1 . At that same aminocyclopyrachlor rate, grass biomass was reduced 0 to 48% and flax and sagebrush species were reduced ≥ 77%. We document variation among and within species for relative tolerance to this herbicide. If aminocyclopyrachlor were used in a restoration project for postemergence control of Russian thistle, most grasses in this experiment would experience negligible biomass reduction whereas the selected sagebrush and flax species were highly susceptible at this early growth stage even at low aminocyclopyrachlor rates.

We have calculated global and local DFT reactivity descriptors for aminocyclopyrachlor herbicide at the MP2/6-311++G (2d,2p) level of theory in the aqueous phase. Global reactivity descriptors such as ionization energy, molecular hardness, electrophilicity, and total energies were calculated to evaluate the aminocyclopyrachlor reactivity. Local reactivity was evaluated through the Fukui function. Our results suggest that the cationic and dipolar forms of aminocyclopyrachlor exhibit similar global reactivity and they are susceptible to deamination and decarboxylation. Also, the opening of the ring might become factible through free radical attacks to the neutral form, while a similar process is caused by nucleophilic attacks on the anionic form.

Miller, A. J., Bork, E. W., Hall, L. M. and Summers, B. 2015. Long-term forage dynamics in pastures sprayed with residual broadleaf herbicide: A test of legume recovery. Can. J. Plant Sci. 95: 43–53. Legumes such as alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.) are important components of northern temperate pastures where they increase forage productivity and quality, but are susceptible to decline when exposed to broadleaf herbicides. Little is known about the long-term sward responses following herbicide use in northern temperate pastures, including the recovery of legumes and their subsequent contribution to forage production. We established five field sites over 2 yr to assess changes in grass, legume, total forage (grass+legume) and other forb biomass, as well as the recovery of a common weed, dandelion (Taraxacum officinale Weber), for up to 3 yr following a single application of two broad leaf herbicides with residual properties (aminopyralid and aminocyclopyrachlor). The importance of defoliation and the legume seed bank in facilitating legume biomass recovery were also evaluated with mowing and legume overseeding, respectively, in a strip/split-split design. Both herbicides had similar functional impacts on sward composition based on peak annual biomass, reducing legume biomass by an average of 71–100% across the 3 yr, equivalent to 63.4–22.6 g m−2 from year 1 to year 3, respectively. Although grass biomass did not change significantly with herbicides, net reductions in total forage were limited to 6.8% (28 g m−2) over the study, suggesting at least some ability of grasses to compensate for legume removal. Legume biomass was greater following overseeding and only in non-sprayed controls, but then decreased over time. Conversely, biomass of other forbs and cover of dandelion were lower shortly following herbicide application, only to reach levels similar to non-sprayed controls by the second growing season. Defoliation also influenced sward composition, favoring dandelion recovery following herbicide application. As both weed control and legume re-establishment are important objectives for livestock producers, the result of this study provides useful insight into the long-term impact of broad-leaf weed control on forage production in mixed swards of northern temperate pastures.

Aminocyclopyrachlor is an herbicide that belongs to the new class of chemicals known as the pyrimidine carboxylic acids, which are used to control broadleaf weeds and brush. However, the environmental behavior and fate of aminocyclopyrachlor are not fully understood. The aim of the present study was thus to evaluate the mineralization, extractable residue and bound residue formation of aminocyclopyrachlor in three tropical soils with different physico-chemical properties. 14C-labeled [pyrimidine-2-14C] aminocyclopyrachlor was used to assess the fate of this herbicide in soil placed in biometer culture flasks. Total mineralization (accumulated 14CO2) of aminocyclopyrachlor was found to be Oxisol—Typic Hapludox (loamy sand) > Plinthosol—Petric (sandy clay). Overall, constant rate of mineralization (k) values for all soils were very low (0.00050% to 0.00079% 14CO2 day−1), with mineralization half-life times (MT50) consequently very high (877 to 1376 days), suggesting potential long persistence in soil. The amount of extractable residues decreased from ~31% to 50% in all soils after 126 days of incubation, indicating an increase in bound residue formation from ~5.0- to 7.5-fold compared to evaluation immediately after herbicide application, suggesting that degradation herbicide is involved in the formation of bound residues. Extractable residues are important factors that control mineralization and bound residue formation from aminocyclopyrachlor in the soil. The present study is the first to assess the fate, distribution, and formation of bound residues of aminocyclopyrachlor in soils. Aminocyclopyrachlor residues were predominantly associated with the OM and clay contents of soil. This effect of soil physico-chemical properties should be considered in environmental risk assessment of aminocyclopyrachlor and its application in the field for weed control.