Khakiweed is a perennial broadleaf weed that is difficult to control because of its multiple means of reproduction, vigorous growth, and deep taproot. Khakiweed reduces the performance of pasture, pecan, and turf areas by choking out desirable grass and legume species. Because information on the effectiveness of contact and residual herbicides for control in pecan and pasture areas is limited, greenhouse studies were conducted to determine the effect of application timing, mode of action, and rate on khakiweed control. Preemergence and postemergence herbicides were applied to mature khakiweed plants at 0.25X, 0.5X, 1X, or 2X the label recommended rate for general broadleaf control. Biomass was collected 3 wk after application. Plants regrew from roots in the greenhouse until a second biomass harvest was collected at 6 wk after treatment (WAT). Metsulfuron-methyl, indaziflam, or pendimethalin was applied preemergence to the soil surface. All rates of preemergence herbicides provided high-efficacy control of regrowth (>85%) compared to the nontreated control. The efficacies of postemergence-applied metsulfuron-methyl, metsulfuron-methyl + nicosulfuron, indaziflam, aminopyralid + florpyrauxifen-benzyl, 2,4-D amine, and 2,4-D amine + florpyrauxifen-benzyl were also examined. All postemergence herbicide treatments exhibited control compared to the nontreated plants at both sample timings (3 and 6 WAT) and increased with herbicide application rate. No herbicide provided high-efficacy control during the initial postspray period (0 to 3 WAT). During the regrowth period (3 to 6 WAT), metsulfuron-methyl alone and in combination gave >85% control of khakiweed biomass, indicating that the sulfonylurea herbicides used in this study are well suited to controlling khakiweed.

Knotroot foxtail has become more prevalent and problematic in pastures and hayfields in the southeastern United States. Gaps exist in our knowledge of which herbicide practices are best for managing this species in bermudagrass forage production. This study was conducted to determine the efficacy of various ways to control knotroot foxtail in bermudagrass with herbicide applications in autumn, postemergence (POST), with and without also applying a herbicide in preemergence (PRE), in spring. The study was a randomized complete block with a factorial arrangement of treatments and included a nontreated control for both fall and spring timings. Glyphosate at two rates (0.35 or 0.7 kg ae ha−1), nicosulfuron (0.07 kg ai ha−1) + metsulfuron (0.012 kg ai ha−1), and hexazinone (1.3 kg ai ha−1) were applied alone in the fall or followed by indaziflam (0.067 kg ai ha−1) or pendimethalin (4.46 kg ai ha−1) in the spring. Three harvests were conducted throughout the growing season to evaluate weed species (knotroot foxtail, large crabgrass, and horsenettle) and bermudagrass biomass as well as overall species composition. The combination of fall and spring treatments did not affect weed species or bermudagrass biomass. Therefore, treatment main effects were analyzed by fall or spring application timing. A spring application of either pendimethalin or indaziflam increased bermudagrass biomass compared with that of the nontreated control. However, neither PRE herbicide effectively reduced knotroot foxtail biomass compared with the nontreated control, although pendimethalin did reduce season-long knotroot foxtail composition. Spring PRE herbicides are an effective tool for forage producers, but further research is needed to identify effective herbicides and additional approaches for the control of knotroot foxtail.

Smutgrass is a non-native perennial weed that is problematic because of its poor palatability to cattle and its difficulty to control once established. Limited literature exists to explain the effectiveness of herbicides other than hexazinone for smutgrass control and forage injury. This study aimed to evaluate seasonal applications of labeled herbicides used on forage for maximum smutgrass control. The second objective was to evaluate preemergent herbicides and hexazinone for their ability to control smutgrass germinating from seed. Hexazinone, nicosulfuron + metsulfuron-methyl, and glyphosate + imazapic were the most effective postemergence treatments, while quinclorac exhibited little activity on smutgrass. Common bermudagrass forage fully recovered from all treatments by 3 mo after treatment. Hexazinone, nicosulfuron + metsulfuron methyl, glyphosate, and imazapic were applied postemergence to smutgrass in spring, summer, and fall. Summer applications of hexazinone resulted in the greatest level of control, while spring treatments provided the least control. Applications of hexazinone or glyphosate resulted in the most effective smutgrass control. However, fall applications resulted in the least forage injury. Results of the study of preemergence herbicides indicate that treatments with indaziflam and hexazinone provide adequate control of germinating smutgrass seedlings in the greenhouse at 0.25×, 0.5×, and 0.75× of the lowest recommended labeled rate for seedling grass control. Indaziflam treatments prevented the emergence of any visible smutgrass seedling tissue, compared to hexazinone, which fully controlled the germinating seedlings by 21 d after treatment, whereas pendimethalin significantly reduced seedling numbers at the 0.5× and 0.75× rates.

Old man’s beard is a woody liana that has become an invasive weed in many areas of its introduction, through its vigorous spread and negative impacts on the tree hosts it climbs. Control techniques that improve precision and reduce non-target damage are increasingly preferred for weed control yet have not been compared in published research for use against old man’s beard. Field experiments in New Zealand were conducted to: (i) assess targeted herbicide techniques for control of this weed’s climbing stems when growing among trees and (ii) assess foliar herbicides for control of creeping stems in ruderal sites. For climbing stems, triclopyr in oil was applied around the circumference of woody stems near their base, which was compared with cutting the stems and applying concentrated glyphosate gel (45% ai) to each cut end. Herbicides were applied in autumn directly to individual stem bases of the weed, thereby protecting tree hosts and other non-target vegetation. The basal application of triclopyr to intact stems was highly effective (>95% mortality) with no damage to nearby trees noted. The glyphosate gel applications to cut stems were less effective (56% mortality by 2 yr after treatment). For creeping stems in grass-dominated ruderal sites, selective foliar herbicide sprays had not been previously juxtaposed to compare control of old man’s beard. Three selective sprays that do not damage existing grass cover were applied in autumn at their recommended rates: (i) metsulfuron; (ii) triclopyr; and (iii) a mixture of triclopyr, picloram, and aminopyralid. All herbicide treatments provided effective control, although metsulfuron had a negative effect on grass vigor, which might allow new establishment of old man’s beard seedlings by competitive release. These results provide effective options that reduce non-target damage for control of both climbing and creeping old man’s beard stems.

Tahitian bridal veil [Gibasis pellucida (M. Martens & Galeotti) D.R. Hunt], a Central and South America native plant that is often confused with another more well-known invasive plant, small leaf spiderwort (Tradescantia fluminensis Vell.), has become invasive in natural areas throughout Florida. However, very little is known regarding herbicide control or other methods. To begin the process of developing herbicide recommendations for land managers who are working to control G. pellucida, multiple postemergence herbicides were screened for efficacy in a shaded greenhouse to determine active ingredients and/or combinations that warrant further investigation under field conditions. Nine different herbicides or combinations, including glyphosate, triclopyr acid, 2,4-D + triclopyr, aminopyralid, 2,4-D, triclopyr amine, metsulfuron-methyl, fluroxypyr, and glufosinate, were applied at standard label rates and compared with a nontreated control group. Visual control ratings were taken at 2, 4, and 8 wk after treatment (WAT), and shoot dry weights were determined at trial conclusion (8 WAT). Data showed glufosinate and triclopyr (acid and amine) provided the highest level of control, as evidenced by control ratings (100% or complete control) and shoot fresh weight reduction, followed by 2,4-D + triclopyr (∼70%) and fluroxypyr (∼50% control). Metsulfuron-methyl and 2,4-D provided the lowest level of control, with results similar to those for nontreated plants on most evaluation dates.

Pondweed is a rhizomatous perennial weed of aquatic habitats that recently adapted to rice ecosystems in northern Iran. Two field experiments were conducted at the Rice Research Institute of Iran to determine the impact of pondweed on rice yield and identify effective herbicides for pondweed control. The focus of the first study was to evaluate the herbicides commonly used in Iranian rice, including butachlor, pretilachlor, oxadiargyl, pendimethalin, thiobencarb, and bensulfuron-methyl. None of these herbicides effectively controlled pondweed, except bensulfuron, which reduced pondweed biomass by ≥95% and produced 26% higher rough rice grain yield than the nontreated plots. The second experiment evaluated the performance of acetolactate synthase–inhibiting herbicides on pondweed control, rough rice yield, and pondweed regrowth. Herbicide efficacy on pondweed varied from 36% to 100%. Five preemergence herbicides, bensulfuron at 45 g ai ha−1, flucetosulfuron at 30 g ai ha−1, triafamone plus ethoxysulfuron at 40 g ai ha−1, and metsulfuron-methyl at 15 g ai ha−1, provided ≥98% control of pondweed. Use of postemergence herbicides penoxsulam at 35 g ai ha−1, bispyribac-sodium at 30 g ai ha−1, and pyribenzoxim at 35 g ai ha−1 provided 36%, 89%, and 93% pondweed control, respectively. Rough rice yields ranged from 107% to 124% in herbicide-treated plots compared with the nontreated plots. Soil-applied herbicide treatments produced higher (≥119%) yield than the hand-weeded control or foliar-applied herbicides. Pondweed regrowth was affected by herbicides and was variable. Soil-applied residual herbicides metazosulfuron, flucetosulfuron, and metsulfuron provided complete control of pondweed and prevented regrowth. In contrast, pondweed regrowth in other soil- and foliar-applied herbicide treatments occurred, indicating their lesser translocation to underground vegetative rhizomes. This study shows that although most sulfonylurea herbicides can control pondweed effectively to achieve high rough rice yield, only a few soil-applied herbicides were able to prevent pondweed regrowth.

In southern Australia, annual sowthistle and prickly lettuce have become more prevalent following the adoption of reduced tillage cropping systems. They are especially problematic in lentil and other pulse crops, which are weakly competitive and have few herbicide options available for POST control of broadleaf weeds. This study aimed to evaluate the influence of management in a previous cereal crop on weed densities in a subsequent crop. At two field sites, crop seeding density and POST herbicide treatments (a conventional choice that included metsulfuron-methyl and MCPA; and a proactive choice that included bromoxynil, picolinafen, and MCPA) were applied to a wheat crop, and weed density was assessed at the beginning of the following season to measure for a legacy effect of the treatments. Study site populations were also screened for herbicide resistance and were found to have high (≥90% survival) ALS inhibitor resistance. Crop competition treatments had no effect on weed populations, and effects of herbicide treatment were significant at only one of the sites. At this site, both herbicide treatments had lower weed densities than the nontreated in the first year, but the legacy effect was only significant for annual sowthistle density in the proactive treatment. At both sites, even where weeds were extremely sparse or completely controlled following herbicide treatment in the first year, moderate densities were observed the following year, indicating that colonization from the seedbank or adjacent areas could be contributing to weed numbers. Weed density assessments and accurate knowledge of the herbicide resistance status of target weeds should guide herbicide selection to maximize control.

Doveweed is a problematic weed species in many agricultural ecosystems as well as on roadsides and rights-of-way. Effective POST chemical control options for doveweed are limited in many cropping systems. Greenhouse studies were conducted to evaluate the effectiveness of metsulfuron-methyl dose and the impact of mixtures and sequential applications of either trifloxysulfuron-sodium or bentazon with metsulfuron-methyl for doveweed control. By 14 d after the initial treatment, applying 0.04 kg ai ha−1 metsulfuron-methyl, either once or sequentially, provided 100% control of doveweed. Application of trifloxysulfuron-sodium at 0.04 kg ai ha−1 alone or in mixture with metsulfuron-methyl (0.04 kg ha−1) did not provide consistent doveweed control nor did it reduce biomass. Trifloxysulfuron-sodium applied alone at 0.08 kg ha−1 or in a mixture with metsulfuron-methyl (0.04 kg ha−1) provided consistent doveweed control (>80%). A single application of bentazon (0.56 kg ai ha−1) was ineffective at controlling doveweed. A single application of the bentazon and metsulfuron-methyl mixture (0.56 + 0.04 kg ha−1, respectively) or sequential applications of either bentazon alone (0.56 kg ha−1) or in mixture with metsulfuron-methyl (0.04 kg ha−1) provided excellent doveweed control (100%) by 35 d after treatment. Overall, single applications of metsulfuron-methyl (0.02 to 0.17 kg ha−1) or mixtures of metsulfuron-methyl with trifloxysulfuron-sodium (0.04 + 0.08 kg ha−1, respectively) or bentazon (0.04 + 0.56 kg ha−1, respectively) controlled doveweed and may be useful for enhancing the control spectrum for other weeds. Sequential applications of the bentazon and metsulfuron-methyl mixture (0.56 + 0.04 kg ha−1, respectively) provided doveweed control and are a resistance-management strategy for doveweed.

POST weed control atop the bed during strawberry production is limited to hand weeding, clopyralid, and acetyl CoA carboxylase inhibitors. Identification of additional modes of action is desirable to increase available options for producers and alleviate herbicide resistance concerns. The study objective was to screen sulfonylurea herbicides for safety of strawberry coordinated with efficacy against Carolina geranium. Herbicide treatments included metsulfuron-methyl, flazasulfuron, foramsulfuron, thifensulfuron-methyl, trifloxysulfuron-sodium, and rimsulfuron. Strawberry plants were heavily damaged by all herbicides apart from foramsulfuron. Although the strawberry plant was dramatically affected by the evaluated herbicides, demonstrating strong epinasty, there were no differences in resultant biomass at 31 d after treatment (DAT) compared to controls. Carolina geranium was severely injured by metsulfuron-methyl, flazasulfuron, and thifensulfuron-methyl, and moderately injured by foramsulfuron. There were consistent reductions in biomass by 31 DAT by metsulfuron-methyl and flazasulfuron. Overall, metsulfuron-methyl and flazasulfuron are suitable candidates for Carolina geranium control in row-middles. Foramsulfuron is a suitable candidate for additional field-based screening for utility in POST use in strawberry production atop the bed. Consideration toward doses, surfactants, timings, and cultivar tolerance may be necessary to minimize injury as observed in the greenhouse (15% to 20%).

Eclipta, widespread in tropical, subtropical, and temperate regions, is one of the main malignant broadleaf weeds and thrives in moist and dryland fields. Field rates of acetolactate synthase (ALS) inhibitors have failed to control eclipta in some farmlands in China. One ALS inhibitor–resistant population (R) collected from Jiangsu province in China was confirmed in the greenhouse in our preliminary work. Whole-plant assays revealed that this R population was highly resistant to four sulfonylureas (pyrazosulfuron-ethyl, 134-fold; bensulfuron-methyl, 172-fold; metsulfuron-methyl, 30-fold; and tribenuron-methyl, 195-fold), two triazolopyrimidines (pyroxsulam, 98-fold; penoxsulam, 30-fold), and one pyrimidinylthio-benzoate (bispyribac-sodium, 166-fold) and was moderately resistant to two imidazolinones (imazethapyr, 10-fold; imazapic, 19-fold). ALS enzyme-activity assays showed insensitivity of the ALS from the R population (resistance index values ranged from 12 to 293) to all of the above ALS inhibitors in vitro. Chromatograms from ALS gene sequence analysis detected a homozygous Pro-197-Ser amino acid substitution in the R population. These results confirmed that the Pro-197-Ser substitution results in broad-spectrum cross-resistance to ALS inhibitors in the eclipta R population. To our knowledge, this study is the first to report broad cross-resistance to ALS inhibitors in eclipta and to obtain the full-length ALS gene sequence.

Parasitic witchweeds inflict most of their damage while still underground and attached to crop roots. Most selective translocated herbicides are detoxified by crops such as corn and thus cannot reach the attached parasites. Corn with target site resistance to acetolactate synthase (ALS)-inhibiting herbicides was tested to ascertain whether these herbicides could control witchweeds, assuming that witchweeds do not obtain amino acids from the crop. Postemergence directed sprays of 27 g ae ha−1 imazapyr 54 d after planting (DAP) delayed Striga asiatica emergence on corn in South Carolina from 3 wk (control) to 7 wk and to 11 wk when mixed with 45 g ae ha−1 AC 263 222. Treatments with up to 71 g ae ha−1 imazamox, and up to 71 g ae ha−1 AC 263 222 only delayed Striga emergence by 1 wk, and 71 g ae ha−1 imazethapyr was ineffective. ALS-inhibiting herbicides were far more effective when applied in 1-ml drenches above the seed at planting. Chlorsulfuron (10 g ai ha−1) and sulfometuron (50 g ai ha−1) were somewhat phytotoxic to Pioneer 3245IR. Rimsulfuron (30 g ai ha−1), metsulfuron (10 g ai ha−1), halosulfuron (120 g ai ha−1), and imazethapyr (140 g ae ha−1) were marginally active in Kenya, with some mature Striga hermonthica seed-bearing capsules appearing at harvest (12 wk). Imazapyr at 15 g ae ha−1 gave 70 to 95% suppression of capsule formation, whereas no capsules appeared at 30 g ae ha−1. The use of imazapyr in Kenya increased the harvest index by 17% when corn plants in Striga-infested soils were kept insect and disease free by using insecticides and fungicides. Thus, complete control can be achieved at affordable cost by farmers in subsistence conditions.

Cut-leaved teasel is an invasive weed along highway corridors and is classified noxious in four states, including Missouri. Few herbicides have been examined for cut-leaved teasel control. Herbicides were evaluated for efficacy on established plants and residual activity for suppressing seedling emergence. Various growth regulator herbicides, amino acid inhibitors, and paraquat were applied on established teasel at two locations in central Missouri in fall 2003 and spring 2004, and two additional locations in fall 2004 and spring 2005. At 2 wk after treatment (WAT), paraquat resulted in the highest injury of teasel (85%), but injury declined over time. At 4 WAT, teasel control was most consistent with dicamba + diflufenzopyr applied in spring, ranging from 75 to 94% control. At 8 wk, glyphosate, dicamba + diflufenzopyr, metsulfuron-methyl, imazapyr, and combinations of growth regulator herbicides with 2,4-D were most effective, with teasel control from 86 to 100%. Control with 2,4-D alone was inconsistent; sulfosulfuron, sulfometuron-methyl, and paraquat were ineffective. Residual herbicides did not reduce teasel seedling emergence the following year. A number of herbicides were effective in managing emerged plants but reinfestations of treated sites is likely, even with the residual herbicides used in this research.

Sulfur cinquefoil is an exotic, perennial forb that invades a wide range of ecosystems in western North America. It forms dense populations and often threatens native plant species and communities. In this study, we address the following questions: (1) what herbicides, rates, and application times are most effective at reducing sulfur cinquefoil abundance while having the least impact on native plants; and (2) does postherbicide seeding with native grass species increase native plant abundance? In 2002, we experimentally examined the effects of five herbicides (dicamba + 2,4-D; metsulfuron-methyl; triclopyr; glyphosate; and picloram) at two rates of application (low and high), three application times (early summer, fall, and a combined early summer–fall treatment), and two postherbicide seed addition treatments (seeded or not seeded) on sulfur cinquefoil abundance, plant community composition, and species richness. Experimental plots were monitored through 2005. Picloram was the most effective herbicide at reducing sulfur cinquefoil density, the proportion of remaining adult plants, and seed production. The effects of picloram continued to be evident after 3 yr, with 80% reduction of sulfur cinquefoil in 2005. In addition, seeding of native grass seeds alone (no herbicide application) reduced the proportion of sulfur cinquefoil plants that were reproductively active. Despite reductions in sulfur cinquefoil abundance, all treatments remained dominated by exotic species because treated areas transitioned from exotic forb- to exotic grass-dominated communities. However, a one-time herbicide application controlled sulfur cinquefoil for at least 3 yr, and therefore might provide a foundation to begin ecological restoration. Herbicide applications alone likely are to be insufficient for long-term sulfur cinquefoil control without further modification of sites through native grass or forb seeding. Integrating herbicides with native plant seeding to promote the development of plant communities that are resistant to sulfur cinquefoil invasion is a promising management approach to ecological restoration.

Japanese climbing fern (Lygodium japonicum) is an invasive vine that has been identified as an economic and ecological threat in forest ecosystems of the Southeast. In two separate studies, we examined the use of directed sprays of glyphosate, imazapyr, and metsulfuron-methyl herbicides, alone and in combination, for control of Japanese climbing fern and for impacts to associated vegetation in mixed bottomland hardwood–cypress forests at two first terrace sites of the Apalachicola River in north Florida. Two yr after treatment, various rates of glyphosate alone generally provided greater percent control (84 to 95%) than imazapyr alone (−25 to 86%) or metsulfuron-methyl alone (−5 to 53%). Combinations of 2% glyphosate and imazapyr and/or metsulfuron-methyl resulted in 81 to 97% control at 2 yr after treatment, with no significant differences among the combination treatments or 2% glyphosate alone. Change in percent cover of associated vegetation groups was not influenced by treatment except for one location where graminoid cover increased 1 yr after metsulfuron-methyl treatment but decreased after imazapyr or glyphosate application. Species richness of dominant understory vegetation remained nearly constant at both locations regardless of treatment. These data indicate that glyphosate alone or in combination with imazapyr or metsulfuron-methyl will provide effective, although not complete, control of Japanese climbing fern, and that directed herbicide sprays minimally impact nontarget vegetation.

Metsulfuron is used for POST control of spotted spurge in many warm-season turfgrasses. A suspected resistant (R) biotype of spotted spurge was collected from turfgrass in Georgia with a history of exclusive metsulfuron use. Research was conducted to evaluate the resistance level of this biotype to metsulfuron, efficacy of other mechanisms of action for control, and the molecular basis for resistance. Compared with a susceptible (S) biotype, the R biotype required >90 and >135 times greater metsulfuron rates to reach 50% injury and reduce biomass 50% from the nontreated, respectively. The R biotype was also resistant to trifloxysulfuron but was injured equivalent to the S biotype from dicamba, glyphosate, and triclopyr. Gene sequencing of the R biotype revealed a Trp574 to Leu substitution that has conferred resistance to acetolactate synthase (ALS) inhibitors in previous research. This is the first report of ALS resistance in spotted spurge. More importantly, this is the first report of a herbicide-resistant broadleaf weed from a turfgrass system in the United States.

Clover inclusion may increase the sustainability of certain low-maintenance turfgrasses. However, selective weed control within mixed turfgrass–clover swards proves problematic because of clover susceptibility to herbicides. Research was conducted to identify common turf herbicides that are tolerated by three Trifolium species, including white clover, ball clover, and small hop clover, within low-maintenance turfgrass. Leaf and flower density, as well as plant height, were measured 4 wk after treatment as indicators of clover response to 14 herbicides. The three Trifolium spp. were moderately tolerant of bentazon (< 35% decrease in leaf density, height, or flowering). Simazine was well tolerated by white clover (< 5% decrease in all response variables), yet moderate injury to ball clover and small hop clover was observed (> 32% decrease in leaf density and > 27% decrease in flower density). Pronamide was well tolerated by white and ball clovers, with no effect on measured response variables; however, pronamide decreased small hop clover height and flower density (38 and 42%, respectively). Imazethapyr and imazamox were moderately well tolerated by white clover and small hop clover (< 39% decrease by all response variables), yet ball clover may be more susceptible to these herbicides than was anticipated based on previously reported tolerance. The herbicides 2,4-DB, halosulfuron, and metribuzin were well tolerated by white clover, with no effect on measured response variables; however, results suggest ball and small hop clovers were less tolerant. Clopyralid, 2,4-D, glyphosate, imazaquin, metsulfuron-methyl, and nicosulfuron resulted in varying degrees of injury across clover species and response variables, but, in general, these herbicides may not be viable options when attempting to maintain any of the three clover species tested. Further research is needed to quantify long-term effects of herbicide application on sward composition and clover succession.

Meadow foxtail is a rhizomatous grass widely grown for hay and pasture in wet meadows of the western United States and Canada. Two sulfonylurea herbicides, chlorsulfuron and metsulfuron-methyl, were evaluated for their effects on meadow foxtail biomass. Both herbicides were applied at four doses, 0.035, 0.070, 0.105, and 0.140 kg ai/ha, together with a control at each of two sites in October 2003. Treatments were replicated four times at each site and arranged in a randomized complete block design and sampled in July 2004 and 2005. Meadow foxtail biomass depended on site (P = 0.001) or year (P = 0.001), but not herbicide treatment (P = 0.182). No biomass production losses resulted from applying up to 0.14 kg/ha of either chlorsulfuron or metsulfuron-methyl on meadow foxtail, even in relatively high-pH soils.

Western salsify has recently formed dense stands in Conservation Reserve Program (CRP) lands in north-central Montana. Our objective was to test the effects of various herbicide treatments and mowing on western salsify and associated vegetation in CRP lands. Six herbicide treatments and one mowing treatment were applied at three sites in 2010. Herbicide treatments included combinations of glyphosate, 2,4-D, dicamba, and/or metsulfuron-methyl applied when western salsify was either in the rosette or early flowering stage. Mowing was applied at the early flowering stage. Herbicide treatments reduced western salsify and increased perennial grass at one of the three sites, which was the site most dominated by western salsify. When dicamba (0.14 kg ae ha−1) plus 2,4-D (0.48 kg ae ha−1) was applied at the rosette stage, western salsify adult plant density and biomass were reduced to zero and perennial grass biomass increased by 108% in 2010. In 2011, western salsify adult plant density was lower across all herbicide treatments compared to the mowed and nontreated plots. Annual grass density increased by up to 400% when herbicide applications including metsulfuron-methyl were applied at the early flowering stage. Mowing did not control western salsify. Results suggest dicamba plus 2,4-D applied at the rosette stage can provide effective control of western salsify and increase perennial grasses without stimulating the emergence of annual grasses.

Two field experiments were conducted at the Agronomy Research Station near Stillwater, OK in 2004 and 2005 to identify and evaluate herbicides applied preplant incorporated, preemergence, early postemergence, or late postemergence for the control of seedling sericea lespedeza. Trifluralin, applied preplant incorporated, controlled seedlings 77 (15 wk after emergence [WAE]) and 63% (16 WAE) in 2004 and 2005, respectively. Flumioxazin, imazapic, fluometuron, diuron, sulfentrazone, atrazine, metribuzin, and metolachlor applied preemergence all provided greater than 86% seedling control at 15 and 16 WAE in both years. Diclosulam, applied preemergent, controlled seedlings 47% at 15 WAE in 2004 and 91% control at 16 WAE in 2005. In 2004, triclopyr, metsulfuron-methyl, glyphosate, picloram, dicamba, and 2,4-D amine plus picloram (tank-mix) applied early postemergence controlled 90 to 100% of the sericea lespedeza seedlings at 15 WAE. However, in 2005, only triclopyr, metsulfuron-methyl, glyphosate, and 2,4-D amine plus picloram (tank-mix) showed greater than 80% control at 16 WAE. Triclopyr, applied late postemergence, controlled seedlings 100% at 15 and 16 WAE, in both years. In 2004, dicamba plus 2,4-D (premix) and glyphosate were the only other herbicides which provided greater than 75% control at 15 WAE. These data suggest that there were preemergence-applied herbicides that were effective for the control of seedling sericea lespedeza. These data also suggest that triclopyr was the most effective postemergence-applied herbicide for the control of seedling sericea lespedeza. The data also showed that the overall level of control of seedling sericea lespedeza decreased as the season progressed and the plant matured.

Field experiments were conducted to evaluate control of 90- to 100-cm-tall ragweed parthenium in a noncropped situation in Haryana State, India, during 2000 and 2001. Atrazine, 2,4-D ethyl ester, atrazine plus 2,4-D, metribuzin, metsulfuron, chlorimuron, glufosinate with and without surfactant, glyphosate with and without surfactant, and glyphosate formulations MON 8793 and 8794 were sprayed on ragweed parthenium. Also, the effect of water quality was studied with flat-fan and flood-fan nozzles using glyphosate and its formulation MON 8793 against ragweed parthenium and associated weeds. Glyphosate MON 8793 and 8794 at 3.6 kg ae/ha provided excellent control of ragweed parthenium followed by glyphosate at 2.7 or 5.4 kg/ha, with no recovery until 18 wk after treatment (WAT). Addition of 0.1% v/v surfactant (MON 0818) to glyphosate at 2.7 kg/ha provided similar control to that of glyphosate alone at 5.4 kg/ha. Other herbicides failed to provide satisfactory control of ragweed parthenium. In the water quality study, glyphosate at 2.7 and 5.4 kg/ha and glyphosate MON 8793 at 2.7 and 3.6 kg/ha provided similar control of ragweed parthenium at 18 WAT. Glyphosate was antagonized less by tap water (0.45 mM Ca) than canal (0.7 mM Ca) and hand-pump water (1 mM Ca). Neither glyphosate nor glyphosate MON 8793 provided good control of purple nutsedge, velvetleaf, garden spurge, threelobe false mallow, jimsonweed, giant milkweed, Indian jujube, or tropical spiderwort, but crowfootgrass, green foxtail, sprawling signalgrass, and spiny amaranth were controlled. Glyphosate at 5.4 kg/ha and glyphosate MON 8793 at 3.6 kg/ha provided more than 80% control of bermudagrass at 8 WAT, which was significantly better than the 2.7 kg/ha rate. Flat-fan nozzles provided better efficacy of applied herbicides than flood-fan nozzles at 4 WAT on ragweed parthenium.