Carolus Linnaeus described common groundsel, Senecio vulgaris, in his Species Plantarum, published in 1753 (2). The generic name is derived from the Latin senex meaning old or old man, the pappus resembling a white beard (4). Vulgaris is from the Latin vulgari meaning common, usual, or ordinary (7, 18).

Yellow nutsedge is a problematic weed in plasticulture strawberry because herbicides and fumigants currently used in California provide little to no control and because nutsedge shoots easily penetrate standard low-density polyethylene (LDPE) mulch to rapidly establish and compete with the crop. Field studies were conducted at two California locations near Oxnard and Camarillo from 2007 to 2009 to evaluate yellow nutsedge control with physical barriers. Nutsedge germinated in both autumn and spring through LDPE mulch alone, but paper placed between two layers of standard 0.15-mm black LDPE mulch, weed barrier fabric commonly used in landscapes placed under LDPE mulch, and Tyvek Home Wrap placed under LDPE mulch suppressed nutsedge emergence. In 1 yr, the size of strawberry plants grown with weed barrier fabric was reduced 23% compared with the other treatments and the number of marketable fruit in the third month of harvest was reduced 20% compared with LDPE mulch alone, likely because inadequately cut planting holes in this barrier restricted plant growth. Estimated costs for barrier treatments ranged from $5,000 to $12,000 ha−1 compared with estimated hand-weeding costs of up to $24,000 ha−1. In 2007 to 2008 barrier treatments reduced the number of wind-dispersed weeds that commonly land and germinate in strawberry planting holes 67% compared with LDPE mulch alone. Removing the barriers at the end of the two seasons revealed that nutsedge plants sprouted but failed to grow and produce new tubers under the barriers. This observation suggests that nutsedge-impermeable barriers may aid in depletion of the soil tuber bank and therefore can be an effective tool in managing nutsedge for the length of the growing season.

Fenoxaprop, fluazifop-P, haloxyfop, quizalofop, and sethoxydim applied postemergence reduced johnsongrass populations in soybeans over a 3-yr period. The selective postemergence herbicides were more effective as split applications than as single, high-rate applications for controlling heavy infestations of johnsongrass. Fluchloralin applied preplant incorporated decreased the number of postemergence applications required to maintain johnsongrass control above 80%, although control depended primarily upon the selective, postemergence herbicides. Glyphosate applied by ropewick reduced johnsongrass populations more when used in conjunction with fluchloralin than when used alone.

Field experiments were conducted in 2003 and 2004 to determine the tolerance of direct-seeded leafy turnip greens, mustard greens, kale, and collard to selected preemergence and postemergence herbicides and to determine the efficacy of these herbicides against weeds that are common to the southeastern coastal plains of the United States. Pendimethalin applied preemergence controlled large crabgrass, goosegrass, carpetweed, and common purslane, but it injured turnip greens, mustard greens, kale, and collard. Dimethenamid at 0.31 and 0.63 kg ai/ha controlled large crabgrass and goosegrass but did not control hairy nightshade or common purslane at the lower rate. In 2003, dimethenamid at 0.63 kg/ha injured mustard greens, kale, and collard more than 40%. S-metolachlor applied preemergence at 0.45 kg ai/ha controlled large crabgrass, goosegrass, hairy nightshade, and common purslane while causing little or no injury to turnip greens, mustard greens, kale, and collard. Clopyralid at 0.10 kg ai/ha controlled common lambsquarters 76 to 95% and hairy nightshade 93% but did not control carpetweed, common purslane, large crabgrass, and goosegrass. Turnip greens, mustard greens, kale, and collard generally were tolerant of clopyralid, but mustard was injured 29% in 2003. Phenmedipham alone or in combination with desmedipham injured mustard greens 54 to 82% in 2003 and failed to control weeds. Of the herbicides evaluated, S-metolachlor provides the best potential to improve weed control in direct-seeded leafy greens in the southeastern United States.

Halauxifen plus florasulam, thifensulfuron plus fluroxypyr, and bromoxynil plus bicyclopyrone are three, relatively new POST premix herbicides developed for control of broadleaf weeds in winter wheat. These herbicides, along with older products, were evaluated for their control of horseweed in Altus, Perkins, and Ponca City, Oklahoma, during the spring of 2017 and 2018. Horseweed has become a critical weed in Oklahoma because of its extensive germination window, changes in tillage practices, and increase in herbicide-resistant horseweed biotypes. Visual weed control was estimated every 2 wk throughout the growing season and wheat yield was collected from three of the six site-years. Horseweed size ranged from 5 to 20 cm at time of application. The halauxifen plus florasulam, and thifensulfuron plus fluroxypyr combinations were effective at controlling a wide range of horseweed rosette sizes across all locations, whereas control with other treatments varied depending on presence of herbicide resistance, weed size at time of application, and mix partner.

Field studies were conducted over six seasons to determine the critical period for weed control (CPWC) in high-yielding cotton, using common sunflower as a mimic weed. Common sunflower was planted with or after cotton emergence at densities of 1, 2, 5, 10, 20, and 50 plants m−2. Common sunflower was added and removed at approximately 0, 150, 300, 450, 600, 750, and 900 growing degree days (GDD) after planting. Season-long interference resulted in no harvestable cotton at densities of five or more common sunflower plants m−2. High levels of intraspecific and interspecific competition occurred at the highest weed densities, with increases in weed biomass and reductions in crop yield not proportional to the changes in weed density. Using a 5% yield-loss threshold, the CPWC extended from 43 to 615 GDD, and 20 to 1,512 GDD for one and 50 common sunflower plants m−2, respectively. These results highlight the high level of weed control required in high-yielding cotton to ensure crop losses do not exceed the cost of control.

Field studies were conducted from 1991 through 1993 to compare Weed control, peanut tolerance, yield, and net return from imazethapyr applied alone or in combination with paraquat. Sicklepod and Florida beggarweed were controlled with paraquat early POST followed by a POST application of either paraquat with 2,4-DB or paraquat with 2,4-DB and bentazon. Imazethapyr-based early POST treatments offered no improvement. An early POST application of paraquat with bentazon or imazethapyr was required for maximum control of bristly starbur. Imazethapyr applied alone early POST, with no further treatment, provided optimum yellow nutsedge control. Maximum yield and net return were associated with any paraquat-containing early POST-applied treatment followed by one of the tank mixed POST options.

The objective of this experiment was to determine the effectiveness and crop safety of glyphosate vs. alternative herbicides for weed control in glyphosate-resistant alfalfa. Glyphosate-resistant alfalfa was established at two sites in Pennsylvania in 2004 and in 2005, and herbicides were applied either PRE or POST for weed control. Data were collected on herbicide performance, alfalfa and weed yield, and forage quality. Alfalfa forage response to weed control was variable and depended on weed severity. A single or split application of glyphosate provided similar or better weed control than conventionally based herbicide programs. The most differences from weed control occurred during the first harvest and dissipated in subsequent harvests. Cumulative alfalfa yield for the establishment year of the spring seeding was 26% lower in the untreated check relative to the mean of the herbicide-treated plots in 2004; but no differences were detected in 2005. Forage quality was highest where weed content of the forage was lowest. Effective management of weeds with herbicides during alfalfa establishment can improve forage yield and quality, and weed control is particularly important when summer annual weed populations are severe and emerge with the crop.

PRE and POST herbicides were evaluated for their effects on root growth of Kentucky bluegrass and tall fescue turf. All PRE treatments, bensulide at 14.0 kg ai ha−1, DCPA at 11.8 kg ha−1, dithiopyr at 0.4 kg ha−1, pendimethalin at 1.7 kg ha−1, and prodiamine at 0.6 kg ha−1, inhibited root growth when cores, 10 cm in diam and 2.5 cm deep, of herbicide-treated Kentucky bluegrass were placed into pots of perlite. Only prodiamine inhibited tall fescue rooting. None of the PRE treatments reduced rooting of grasses when 10-cm diam and 16-cm deep cores were sampled from the field. No differences in rooting were observed among any of the POST treatments on either species.

The dissipation of trifloxysulfuron in solution has not been evaluated. The objectives of this study were to evaluate the effect of spray carrier pH (pH values of 5, 7, and 9) on dissipation of trifloxysulfuron during a 21-d period and to evaluate the resulting effects on efficacy on Palmer amaranth. ANOVA of half-life values indicated that hydrolysis occurred more rapidly under acidic spray carrier pH with no differences between neutral and alkaline pH levels. Trifloxysulfuron solutions that were applied to Palmer amaranth significantly decreased dry weights compared with nontreated at all pH levels and time intervals. These results indicated that trifloxysulfuron dissipation was most rapid when the spray tank pH was more acidic, but trifloxysulfuron efficacy was not adversely affected by chemical degradation on Palmer amaranth. Data suggest that pesticide applicators may reduce trifloxysulfuron degradation in spray tanks by using neutral or alkaline spray carriers.

Many herbicides that control broadleaf weeds in wheat can antagonize grass herbicide efficacy, resulting in less grain yield due to competition. Also, the broadleaf herbicide carfentrazone-ethyl can injure wheat, leading to less grain yield because of physiological response. Experiments were conducted to evaluate carfentrazone-ethyl antagonism of fenoxaprop-ethyl, tralkoxydim, clodinafop-propargyl, imazamethabenz, and flucarbazone-sodium and injury to wheat with tank mixes of carfentrazone-ethyl plus each grass herbicide or thifensulfuron, tribenuron, metsulfuron, or imazamox. Carfentrazone-ethyl did not adversely affect control of wild oat or yellow foxtail by grass herbicides in wheat. Carfentrazone-ethyl alone caused 21% wheat injury 3 d after treatment. Adding flucarbazone-sodium to carfentrazone-ethyl resulted in the least wheat injury among treatments that included carfentrazone-ethyl. Fenoxaprop-P-ethyl or clodinafop-propargyl with carfentrazone-ethyl also resulted in less wheat injury compared with carfentrazone-ethyl alone, which was attributed to formulation safeners. Sulfonylurea herbicides provided safening of carfentrazone-ethyl similar to flucarbazone-sodium, while imidazolinones did not alleviate injury. Tralkoxydim plus carfentrazone-ethyl gave 28% wheat injury compared with 21% from carfentrazone-ethyl alone. Wheat injury was no longer visible by 20 d after treatment, and wheat yield was not affected by carfentrazone-ethyl injury when wild oat and yellow foxtail were present or controlled with herbicide.

Field studies were conducted at Aberdeen, ID; Ontario, OR; and Paterson, WA, to evaluate potato tolerance to flumioxazin and sulfentrazone. In ‘Russet Burbank’ tolerance trials conducted in 2000 at ID, OR, and WA, sulfentrazone applied preemergence (PRE) at rates ranging from 105 to 280 g ai/ha caused significant injury consisting of stunting, leaf discoloration-blackening, and/or leaf malformation-crinkling at 4 wk after treatment (WAT). By 12 WAT, injury was ≤5%. At 4 WAT, flumioxazin applied PRE at 105 and 140 g ai/ha resulted in injury, whereas 53 g ai/ha did not cause significant injury. At 12 WAT, no visual injury was present at the ID site, whereas flumioxazin at 140 g/ha was still causing injury in WA. Regardless of initial injury, Russet Burbank tuber yields at ID, OR, and WA were not reduced as a result of any flumioxazin or sulfentrazone treatment compared with the nontreated controls. In potato variety tolerance trials conducted at ID in 2000 and at WA in 2002 with Russet Burbank, ‘Ranger Russet’, ‘Russet Norkotah’, and ‘Shepody’ and at ID in 2002 with those varieties plus ‘Alturas’ and ‘Bannock Russet’, early season injury caused by flumioxazin or sulfentrazone applied PRE at rates as high as 210 g ai/ha or 280 g/ha, respectively, occurred, but variety tuber yields were not reduced compared with nontreated control yields. In contrast, at ID in 2001, early injury caused by flumioxazin or sulfentrazone applied PRE at 105 or 210 g/ha translated to tuber yield reductions of all six varieties tested compared with the nontreated controls. At WA in 2001, Ranger Russet tuber yields were reduced by PRE applications of flumioxazin at 53 to 140 g/ha or sulfentrazone at 105 to 280 g/ha, and Shepody total tuber yields were reduced by all rates of PRE-applied sulfentrazone. Russet Burbank and Russet Norkotah tuber yields were unaffected by either herbicide. Unusual heat stress occurring early in the 2001 growing season at both locations may have compounded the effects of herbicide injury and, consequently, tuber yields were reduced in 2001, whereas injury occurring in 2000 or 2002 during relatively normal growing conditions did not translate to yield reductions.

Safflower (Carthamus tinctorius L. ‘Hartman’) in the rosette growth stage or early bolting stage tolerated thiameturon {3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] amino] sulfonyl]-2-thiophenecarboxylic acid} at 5, 10, and 15 g ai/ha. Safflower also tolerated chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} at 18 g/ha if safflower was taller than 15 cm at time of application. The fresh weight of above-ground biomass of common sunflower (Helianthus annuus L. #3 HELAN), treated at two plant sizes with thiameturon, was reduced more than 88%. Soil activity of thiameturon also reduced the seedling vigor of common sunflower, but thiameturon in soil was not as lethal to common sunflower as were foliar applications.

Greenhouse and field experiments were conducted in North Dakota to determine the effect of adjuvants applied with imazapic on the control of leafy spurge and production of various grass species and to determine the most effective fall-application timing of imazapic for optimum leafy spurge control with minimal effect on herbage. Imazapic applied with a methylated seed oil (MSO) adjuvant tended to provide greater leafy spurge control than when applied with other types of adjuvants. Imazapic applied alone or with adjuvants reduced production of some grass species in the greenhouse, but it did not decrease herbage production in the field. Imazapic at 140 g/ha applied with MSO or with 28% N plus MSO averaged 72% leafy spurge control 12 mo after treatment, compared to 33% control from imazapic alone and 40% control from picloram plus 2,4-D. Imazapic at 140 g/ha applied with MSO in mid-September provided greater leafy spurge control compared to August or October applications.

Soybean-based [Glycine max (L.) Merr.] and petroleum-based crop oil concentrates were equally effective as spray adjuvants for control of quackgrass [Agropyron repens (L.) Beauv. #3 AGRRE] with the butyl ester of fluazifop {[±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} and sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}. With favorable growing conditions at application in 1983 and 1985, an adjuvant concentration of 1% (v/v) with these herbicides was adequate for quackgrass control. Unfavorable growing conditions at application in 1984 resulted in unacceptable quackgrass control, and spray volume did not affect control. However, increasing the adjuvant concentration to 4% (v/v) with either herbicide applied in a spray volume of 70 L/ha nearly doubled quackgrass control. In 1983 and 1985, equal or greater quackgrass control with each herbicide was achieved with spray volumes as low as 35 L/ha compared to 280 L/ha.

Field trials were initiated at three Missouri locations in the fall of 2004 and 2005 to compare the efficacy of fall and early spring herbicide applications on winter and summer annual weed populations in no-till soybean. All three experiments received applications of chlorimuron plus sulfentrazone plus 2,4-D; chlorimuron plus tribenuron plus 2,4-D; and glyphosate plus 2,4-D in the fall, 60 d prior to planting (60 PP), 30 days prior to planting (30 PP), and 7 d prior to planting (7 PP). Good control of all winter annual weeds, except for common chickweed, was observed at planting from fall applications of chlorimuron plus sulfentrazone plus 2,4-D and chlorimuron plus tribenuron plus 2,4-D. Fall, 60 PP, and 30 PP applications of chlorimuron plus sulfentrazone plus 2,4-D provided relatively poor control of common chickweed. Glyphosate plus 2,4-D applied in the fall and 60 PP provided adequate control of early fall germinating winter annuals, such as common chickweed and henbit. However, these treatments provided poor control of winter annual species that exhibited some degree of spring germination. Control of summer annual weed species 7 wk after planting (WAP) was highly variable. Relatively poor control of common waterhemp was obtained from all treatments except chlorimuron plus sulfentrazone plus 2,4-D applied at all three spring timings. Giant foxtail control was highly variable ranging from 0 to 95%. Measurements of weed biomass collected 7 WAP revealed larger amounts of biomass present in the fall application timing of each herbicide treatment. Emergence of winter and summer annual weed species from early March to 7 WAP varied by herbicide treatment. Emergence of total winter and summer annual weed species was reduced with both residual herbicide treatments when compared with glyphosate plus 2,4-D and the untreated control.

A field study was conducted at two sites in southwestern Ontario, Canada, from 2002 to 2005 to assess the cumulative effects of different weed management strategies applied to the same plots over time in a corn–soybean rotation. These strategies included a POST broad-spectrum herbicide applied at recommended or reduced rates and use of a computer decision aid to select the POST herbicide having the greatest net return (economic threshold approach) based on weed populations before treatment or seed-bank estimates. Four years after study initiation, increased weed populations were observed only in the nontreated control. The reduced rate and economic threshold approaches did not lead to increased weed seed banks compared with the recommended rate of a broad-spectrum herbicide. Reductions in herbicide rate were more effective than the use of economic thresholds for reducing the risk of environmental impact in corn and soybeans. Weed populations in this study were generally above threshold levels, and herbicides selected by the computer decision aid tended to be older, less-expensive herbicides with high use rates. Recommendations by the computer decision aid were generally more effective and more profitable when based on weed populations before treatment than when based on seed-bank estimates.

Two introduced windgrass species have become crop weeds in North America. Common windgrass is a major weed of winter cereals in Europe and was first documented in North America in the early 1800s. It is a weed of roadsides and waste areas in the northeastern United States and in winter grain fields of southern Ontario and Michigan. Interrupted windgrass was first reported in North America approximately 90 yr ago; it is adapted to more arid sites than common windgrass and is distributed predominantly in the northwestern U.S.A. During the past 10 to 15 yr, interrupted windgrass has adversely affected winter grain and grass seed producers in the Pacific Northwest due to additional control costs.

Current environmental concerns demand intensive research on conservation tillage for cotton production. Studies were conducted in 1994 and 1995 at Florence, SC, to evaluate weed and cotton response to various weed management systems in cotton with reduced tillage. Broadcast application of pendimethalin at 1.1 kg ai/ha and fluometuron at 2.2 kg ai/ha preemergence (PRE) followed by pyrithiobac at 0.07 kg ai/ha early postemergence (EPOST) was more effective than was a 38-cm band of these herbicides in controlling naturally occurring populations of sicklepod, Palmer amaranth, goosegrass, and southern crabgrass and in providing cotton yields equal to yields under weed-free conditions. With the 38-cm band of PRE and EPOST herbicides, two supplemental weed treatments at 3 and 7 wk after planting using glyphosate applied at 0.84 kg ae/ha POST with a hooded sprayer or a no-till cultivator was required to achieve acceptable weed control, but cotton yields were less than yields for the broadcast treatment alone. Glyphosate- or cultivation-only systems were generally ineffective in reducing weed interference and precluding cotton yield reductions. Optimum cotton production with reduced tillage can be achieved with broadcast application of PRE and EPOST herbicides but alternative methods offer promise for reducing costs and environmental effects and deserve additional study.

Broad-spectrum weed control options for pea are limited. Field experiments conducted from 1998 to 2000 evaluated reduced rates of imazethapyr for selective control of grass and broadleaf weed species in pea. Imazethapyr was applied preemergence (PRE) and postemergence (POST) at 20, 40, 60, 80, and 100% of the PRE rate of 75 g ai/ha currently labeled in Ontario. A rate of 45 g/ha or greater was required to maintain consistent control of common lambsquarters and wild mustard when imazethapyr was applied PRE. Green foxtail and redroot pigweed control was excellent at all PRE rates 56 d after treatment. The 75-g/ha rate was required to maintain effective and consistent control of common ragweed. No injury or yield reductions were observed for any of the PRE application rates of imazethapyr. Reduced rates as low as 30 g/ha of imazethapyr applied POST maintained high levels of weed control. Pea tolerance to low rates of imazethapyr applied POST was acceptable except when applied in a year of low rainfall when peas experienced moisture stress.