Field studies were conducted from 1995 through 1998 to evaluate citronmelon control with postemergence (POST) herbicides. Imazapic at any application timing and late postemergence (LPOST) applications of 2,4-DB were the only herbicides that provided >80% control of citronmelon late season. Other herbicides such as acifluorfen, imazethapyr, lactofen, and pyridate provided acceptable (>75%) early-season control of citronmelon, but control was inadequate at harvest.

Field studies were conducted in 2013 at Houlka, MS and 2014 at Houston and Pontotoc, MS to determine the influence of yellow nutsedge density on 'Beauregard' sweet potato yield and quality. Treatments established 2 wk after transplanting (WAP) were yellow nutsedge densities of 0, 5, 10, 15, 30, 40, 50, and 90 shoots m−2 within the planted row. No. 1 and marketable yield loss were fit to a rectangular hyperbola model. In 2013 predicted yield loss of no. 1 and marketable grades ranged from 23 to 96% and 18 to 80%, respectively for yellow nutsedge densities of 5 to 90 shoots m−2. In 2014 predicted yield loss of no. 1 and marketable grades ranged from 7 to 74% and 6 to 67%, respectively for yellow nutsedge densities of 5 to 90 shoots m−2. Yellow nutsedge shoot density increased linearly from 2 WAP to harvest. At Houston and Pontotoc, yellow nutsedge shoot density increased 2.3 and 7.6 times, respectively, for every one shoot present at 2 WAP.

A survey was conducted in 2012 across 13 counties in the eastern Arkansas–Mississippi Delta area on 489 randomly selected road sites to assess the distribution of the most commonly occurring arable weeds. Among the 36 species recorded, Palmer amaranth, johnsongrass, large crabgrass, barnyardgrass, prickly sida, and broadleaf signalgrass were the top six weed species, occurring at 313, 294, 261, 238, 176, and 136 sites, respectively. Barnyardgrass, johnsongrass, and Palmer amaranth were present at 34, 32, and 31% of all sampling occasions (site by roadside topographical characteristic). Habitat preferences varied between weed species. Palmer amaranth, large crabgrass, and johnsongrass exhibited a preference for disturbed habitats as well as field shoulders. Conversely, barnyardgrass, yellow nutsedge, hemp sesbania, and giant ragweed exhibit a preference for moist environments similar to these found in roadside ditches. Herbicide use on roadsides is subject to many environmental regulations and public concerns that, in combination with the evolution of herbicide resistance, necessitate an effective plan for managing agronomically important weed species on eastern Arkansas–Mississippi Delta roadsides.

Largeleaf lantana is a perennial shrub that commonly infests pastures, roadsides, and natural areas. Many experiments have been conducted to manage this weed, but few successful herbicides have been found. Little information is available for the effectiveness of fluroxypyr, aminopyralid, or aminocyclopyrachlor on largeleaf lantana. Experiments were conducted in central Florida on dense, natural infestations of largeleaf lantana. Aminopyralid (0.12 kg ha−1), fluroxypyr (0.56 kg ha−1), and aminocyclopyrachlor (0.2 kg ha−1) were either applied in the fall (approximately 2 mo before frost) or in the fall followed by a spring application. Aminopyralid was ineffective on largeleaf lantana, and neither one nor two applications resulted in > 20% control 1 yr after treatment (YAT). Fluroxypyr applied once in the fall resulted in 12% control at 1 YAT, but two applications resulted in 80% control after 1 yr. The combination of fluroxypyr + aminopyralid, applied twice, resulted in approximately 90% control 1 YAT. A single application of fluroxypyr + aminopyralid failed to provide greater than 20% control. Conversely, aminocyclopyrachlor applied once in the fall provided 98% control of largeleaf at 1 YAT. Where aminocyclopyrachlor was applied twice, largeleaf lantana control was 100%. From these data, largeleaf lantana can be effectively controlled by two applications of fluroxypyr, two applications of fluroxypyr + aminopyralid, or a single application of aminocyclopyrachlor. Individual plant treatments were also investigated using herbicides applied as basal or cut surface applications. At 1 YAT, only triclopyr + aminopyralid provided > 90% control as a basal application. The other herbicide combinations appeared to be effective earlier, but significant regrowth had occurred by 1 YAT. Cut surface applications were similar with triclopyr + aminopyralid and triclopyr + fluroxypyr providing effective control. Neither triclopyr alone nor imazapyr provided effective control for 1 YAT with basal or cut surface applications.

Methyl bromide has been widely used for weed control in polyethylene-mulched tomato production. With the phaseout of methyl bromide in the United States, an effective alternative is needed. Field experiments were conducted in 2007 and 2009 to determine if allyl isothiocyanate (ITC) would provide substantive weed control in tomato along with crop tolerance under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulch. Treatment factors included two mulch types (LDPE and VIF) and six rates of allyl ITC (0, 15, 75, 150, 750, 1,500 kg ha−1). A standard treatment of methyl bromide : chloropicrin (67 : 33%) at 390 kg ha−1 under LDPE mulch was also established. Allyl ITC was broadcast applied and incorporated in soil before forming raised beds and laying plastic mulch. Tomatoes were transplanted 3 wk after applying allyl ITC or methyl bromide treatments. Tomato injury was ≤ 8% in all treatments at 2 wk after transplanting (WATP). Allyl ITC at 913 (± 191) kg ha−1 was required to control yellow nutsedge, Palmer amaranth, and large crabgrass equivalent to methyl bromide at 6 WATP and maintain marketable tomato yield equivalent to methyl bromide treatment. VIF mulch was not effective in increasing weed control or improving the marketable yield of tomato over LDPE mulch. This research demonstrates that allyl ITC under an LDPE mulch can have a practical application for weed control in polyethylene-mulched tomato in the absence of methyl bromide.

Glyphosate-resistant (GR) horseweed is one of the most common and troublesome weeds in soybean production fields in several states in the United States, including Nebraska. The evolution of horseweed resistant to several herbicide sites of action has prioritized an integrated approach, including tillage, for effective management of this problem weed. The objectives of this study were to evaluate the effect of tillage or herbicide applied in fall or spring followed by a PRE, POST, and PRE followed by a POST herbicide program for GR horseweed control as well as GR soybean injury and yield in Nebraska. Field studies were established in the fall 2014–2015 and 2015–2016 growing seasons using a factorial randomized complete block design with shallow tillage or herbicide applied at different timings as two factors. Shallow tillage was accomplished using a 50-cm-wide rototiller operated at a depth of 10 cm. At soybean harvest, tillage applied the previous year in fall or spring without any follow-up herbicide treatment provided 79% to 88% horseweed control compared with 27% and 56% control with 2,4-D plus carfentrazone applied in fall and spring, respectively. Tillage or herbicide applied in fall or spring followed by a PRE, POST, or PRE and POST herbicide provided 82% to 99% GR horseweed control at soybean harvest. Soybean yield in this study was similar in most treatments. Tillage or herbicide applied in fall or spring provided similar horseweed control and soybean yield when followed by a PRE, POST, or PRE and POST herbicide; therefore, fall- or spring-applied herbicides can be rotated with shallow tillage for integrated season-long horseweed management.

Palmer amaranth, a dioecious summer annual weed species, is the most troublesome weed in agronomic crop production systems in the United States. Palmer amaranth resistant to photosystem (PS) II- and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors is of particular concern in south central Nebraska. The objectives of this study were to determine the effect of PRE followed by POST herbicide programs on PS II- and HPPD-inhibitor-resistant Palmer amaranth control, crop yield, and net economic return in conventional corn. A field study was conducted in 2014, 2015, and 2016 in a grower’s field infested with PS II- and HPPD-inhibitor-resistant Palmer amaranth near Shickley in Fillmore County, Nebraska. A contrast analysis suggested that mesotrione+S-metolachlor+atrazine applied PRE provided 83% Palmer amaranth control at 21 d after application compared to 78 and 72% control with pyroxasulfone+fluthiacet-ethyl+atrazine and saflufenacil+dimethenamid-P, respectively. Most of the PRE followed by POST herbicide programs provided ≥85% Palmer amaranth control. Based on contrast analysis, POST application of dicamba+diflufenzopyr provided 93% Palmer amaranth control compared to 87, 79, and 42% control with dicamba, dicamba+halosulfuron, and acetochlor, respectively, at 28 d after POST. All PRE followed by POST herbicide programs, aside from mesotrione+S-metolachlor+atrazine followed by acetochlor (2,530 to 7,809 kg ha−1), provided 9,550 to 10,500 kg ha−1 corn yield compared with 2,713 to 6,110 kg ha−1 from nontreated control. Similarly, PRE followed by POST herbicide programs, except for mesotrione+S-metolachlor+atrazine followed by acetochlor ($191 and $897 ha−1), provided similar net return of $427 to $707 ha−1 and $1,127 to $1,727 ha−1 in 2014 and 2015-16, respectively. It is concluded that herbicide programs based on multiple sites of action are available for control of PS II- and HPPD-inhibitor-resistant Palmer amaranth in conventional corn.

Winter bentgrass is a common, shallow-rooted perennial weed of lowbush blueberry fields. This unique production system is typically managed on a biannual cycle with blueberry shoot growth and floral bud development occurring in the first year (vegetative year) and berries harvested in the second year (crop year). An experiment was conducted in two commercial blueberry fields to determine the impact of 0, 143, or 286 kg ha−1 of 14–18–10 fertilizer applied in the vegetative year, and fluazifop-P applications in the vegetative, crop, or both years of the biannual production cycle, on winter bentgrass and blueberry growth and yield. Fluazifop-P tended to reduce winter bentgrass biomass at both sites and the vegetative year-herbicide applications had a greater impact on winter bentgrass ground cover than crop-year applications. Total weed biomass following fluazifop-P applications was reduced in the vegetative year but not the crop year due to an increase in broadleaf weed biomass. Grass biomass tended to increase with fertility inputs in the vegetative year. In all years and sites, the application of fertilizers without herbicides increased grass biomass compared to the use of fertilizers combined with herbicides. Blueberry floral bud numbers per stem, flowers per stem, and berry yield tended to increase with vegetative year applications of fluazifop-P, although differences were not significant. These data indicate that winter bentgrass management is best achieved with herbicide applications in the vegetative year and this might result in yield increases, especially if broadleaf weeds also are adequately controlled.

Glufosinate controls glyphosate-resistant Palmer amaranth, but growers struggle to make timely applications. XtendFlexTM cotton, resistant to dicamba, glufosinate, and glyphosate, may provide growers an option to control larger weeds. Palmer amaranth control and cotton growth, yield, and fiber quality were evaluated in a rescue situation created by delaying the first POST herbicide application. Treatments consisted of two POST applications of dicamba plus glufosinate, separated by 14 d, with the first application timely (0-d delay) or delayed 7, 14, 21, or 28 d. All treatments included a layby application of diuron plus MSMA. Palmer amaranth, 14 d after first POST, was controlled 99, 96, 89, 75, and 73% with 0-, 7-, 14-, 21-, or 28-d delays, respectively. Control increased following the second application, and the weed was controlled at least 94% following layby. Cotton yield decreased linearly as first POST application was delayed, with yield reductions ranging from 8 to 42% with 7- to 28-d delays. Delays in first POST application delayed cotton maturity but did not affect fiber quality.

Five herbicides were tested in green pea, and their residual effects on several rotational crops were investigated in northwestern Washington from 1998 through 2000. In both years, imazamox applied postemergence caused 21 and 28% early-season injury at 0.036 and 0.045 kg/ha, respectively, but only in 1999 did early-season injury result in yield loss compared with nontreated, weedy pea. Trifluralin, clomazone, and sulfentrazone caused 15 to 19% injury to pea in 1998 but not in 1999. Although pea treated with sulfentrazone produced more harvestable pods than nontreated pea (5.0 and 4.1 pods/plant, respectively), pod numbers were similar to peas treated with clomazone, pendimethalin, pendimethalin plus imazamox, or trifluralin. All rotationally grown crops were tolerant to herbicides used in green pea, except for strawberry in 1999, in which leaf area was reduced 23% in plots treated with 0.045 kg/ha imazamox compared with nontreated plots. Intensive tillage combined with favorable soil and climatic conditions in this study indicate that western Washington green pea producers may have greater flexibility in their choice of herbicides and rotational crop alternatives than previously believed.

Oriental mustard seed meal (MSM), a byproduct generated by pressing the seed for oil, exhibits herbicidal properties. In turfgrass, soil fumigants such as methyl bromide are used to control weeds prior to renovation of turf. Environmental concerns have resulted in deregistration of methyl bromide, prompting the need for alternatives. The objective of this research was to determine the effect of MSM on the establishment of selected turfgrass weeds as well as inhibitory effects on establishment of desirable turfgrasses. Greenhouse experiments were conducted in 2006 and 2007 at the University of Missouri. MSM was amended in soil at 0, 1,350 (low), 2,350 (medium), and 3,360 kg ha−1 (high) concentrations. Weed species included annual bluegrass, large crabgrass, buckhorn plantain, white clover, and common chickweed. Turfgrass species included: Rembrandt tall fescue, Evening Shade perennial rye, and Riviera bermudagrass. All species were seeded into soil amended with MSM and either tarped or left untarped. All treatments were compared to dazomet (392 kg ha−1), a synthetic standard. Plant counts and biomass of all species were recorded 4 wk after seeding. Overall, tarped treatments suppressed weed emergence 27 to 50% more compared to untarped treatments, except for large crabgrass. High rates of MSM suppressed emergence of all weeds ≥ 63%. Compared to the untreated control, the density of buckhorn plantain, white clover, and common chickweed was reduced by ≥ 42% at low rates of MSM. Biomass of buckhorn plantain, annual bluegrass, common chickweed, white clover, and large crabgrass was reduced from 37 to 99% at high rates of MSM. MSM at high rates reduced stand counts of tall fescue and perennial ryegrass up to 81% and 77% respectively, compared to the untreated control. Regardless of MSM rates or tarping, suppression of common bermudagrass emergence did not exceed 30%; tarped treatments actually increased bermudagrass emergence by 22%. The biomass for tall fescue, perennial ryegrass, and bermudagrass was reduced by 85, 68, and 10%, respectively, at high rates of MSM. For tall fescue, MSM at all rates strongly suppressed seed germination by 7 d after planting (DAP) (up to 100%), with additional germination observed through 14 DAP, but not thereafter. In both trials, dazomet completely suppressed emergence of all weeds. MSM appears to suppress emergence and growth of a number of weeds common in turf, with potential selectivity for bermudagrass.

Field research was conducted in 2002 and 2003 to determine the effect of twin- and single-row spacing and POST glyphosate application timing on light interception, weed control, and grain yield of glyphosate-resistant corn and soybean. Row spacing did not affect light interception measured 10 to 11 wk after planting. Corn grain yield in 2002 was 1.0 Mg/ha higher in single rows compared with twin rows when averaged over glyphosate timing, but was unaffected by row spacing in 2003. Soybean grain yield was similar in 19- and 38-cm single rows, and single-row grain yield was 0.2 to 0.4 Mg/ha higher than the twin-row spacing. Corn grain yields were similar to the weed-free control when glyphosate was applied to weeds 10 to 15 cm tall in 2002 and 10 cm tall in 2003. Soybean yield was maximized by application of glyphosate to weeds 15 to 30 cm tall in 2002 and 60 cm tall in 2003.

Herbicides from several chemical families were evaluated in the greenhouse for preemergence control of perennial weed species emerging from seeds. Weed species were bermudagrass, johnsongrass, Canada thistle, common milkweed, common pokeweed, hemp dogbane, and horsenettle. Atrazine, cloransulam, chlorimuron, clomazone, flumetsulam, imazaquin, linuron, metolachlor, metribuzin, pendimethalin, and sulfentrazone were used representing common preemergence herbicide families used in the mid-Atlantic region for corn and soybean in a sandy loam soil. Hemp dogbane and common pokeweed were controlled (greater than 85%) by eight of the 11 herbicides in this study, indicating they may be the two most susceptible species in the trial. Metolachlor and pendimethalin provided control of only bermudagrass, and linuron controlled only Canada thistle. Cloransulam controlled all species except bermudagrass. Clomazone provided greater than 80% control of all species except horsenettle. Metribuzin alone or in combination with chlorimuron provided the broadest spectrum and highest level of control. Metribuzin provided greater than 85% control of all species except johnsongrass. Soil-applied herbicides can limit the establishment of perennial species from seeds.

Experiments were conducted at three locations in Louisiana in 2002 and 2003 to evaluate flumioxazin (36, 72, or 109 g ai/ha) applied pretransplant (PRE) or post-transplant (POST) to sweetpotato. All treatments were applied immediately before or after sweetpotato transplanting to weed-free beds. PRE applications caused 4% or less injury with any rate of flumioxazin at 9 or 18 d after transplanting (DATr) compared with 18 to 20% injury at 9 DATr and 6 to 14% at 18 DATr with 72 or 109 g/ha POST, respectively. Injury from PRE applications of flumioxazin were not different from injury with clomazone (840 g ai/ha) applied POST. Injury at Chase, LA, in 2002 was 8% and less with flumioxazin PRE, but 35 to 83% with flumioxazin POST and appeared to be due to the use of greenhouse-grown cuttings instead of field-grown cuttings, which were used in the other two experiments. There was no interaction between experiments for sweetpotato yield. Plots treated with flumioxazin PRE or 36 g/ha POST yielded greater than sweetpotato treated with clomazone for U.S. No. 1 and 2 grade yield as well as total marketable yield. No differences were observed in yellow nutsedge control with any rate of flumioxazin. At 34 or 50 DATr, flumioxazin controlled yellow nutsedge 73 to 85% with 72 or 109 g/ha applied PRE or POST. Flumioxazin, regardless of application timing or rate, controlled carpetweed and spiny amaranth at least 86%. A similar experiment in Mississippi evaluated tank-mixes of flumioxazin (36, 72, or 109 g/ha) and clomazone (840 g/ha) applied PRE or POST. No sweetpotato injury was observed with flumioxazin PRE. However, injury from flumioxazin POST increased with increased rates (18 to 50% at 18 DATr and 16 to 93% at 25 DATr). Weed control was greater than 80% with all treatments.

Corn inbreds are often more sensitive to herbicides than hybrids. Field experiments were conducted with three corn inbreds to (1) evaluate inbred sensitivity to the acetamide herbicides acetochlor, dimethenamid, flufenacet, and metolachlor, (2) compare the effects of various crop safeners in combination with acetochlor and metolachlor, and (3) measure the effect of herbicide microencapsulation on acetochlor injury. Herbicides were applied preemergence at the registered rate and at two, three, or four times the registered rate in corn. Injury ratings, plant population, and the percentage of plants showing acetamide injury symptoms were used to measure herbicide effect. The inbreds ‘Mo17’ and ‘Great Lakes 15’ (GL15) were sensitive to acetamide injury. Reductions in plant population and increases in the injury rating and the percentage of injured plants were caused by acetochlor, dimethenamid, flufenacet, metolachlor, and flufenacet + metribuzin when applied at three times the registered rate. The inbred ‘B73’ was not injured. The safeners benoxacor and dichlormid reduced injury caused by metolachlor. The percentage of plants injured by metolachlor 15 days after treatment (DAT) was lower when benoxacor was the safener compared to dichlormid. By 28 DAT, plants treated with safeners recovered from injury, and there were no differences between the treatments. The safeners dichlormid and furilazole reduced, but did not always eliminate, injury caused by acetochlor applied at three times the registered rate. Microencapsulation of acetochlor reduced injury to GL15. When the safeners dichlormid or furilazole were included in an acetochlor formulation, microencapsulation did not further reduce corn injury.

Imazamox ammonium salt at 53 g ae/ha applied postemergence in the fall to imidazolinone-resistant wheat controlled Italian ryegrass 98 to 100% 10 wk after treatment (WAT). Control 22 WAT was 88 to 98% at two locations and 55% at a third location. Imazamox was more effective applied in fall to three- to four-leaf Italian ryegrass than when applied in spring to one- to three-tiller Italian ryegrass. Split applications, with 27 g/ha applied in fall and spring, were no more effective than 53 g/ha applied in fall. Pendimethalin preemergence in combination with fall-applied imazamox increased control 22 WAT 10 to 33 percentage points at two of three locations. Imazethapyr ammonium salt plus imazapyr isopropylamine salt applied at 47 plus 16 g ae/ha and imazamox at 44 or 53 g/ha were similarly effective, whereas imazethapyr at 70 g/ha was ineffective. Control by imazapic ammonium salt at 70 g ae/ha was equal to or greater than control by imazamox at 44 or 53 g/ha. Imazamox, imazethapyr plus imazapyr, and imazapic controlled diclofop-resistant and -susceptible Italian ryegrass. Thifensulfuron plus tribenuron mixed with imazamox increased Italian ryegrass control in field and greenhouse experiments, whereas dicamba reduced control compared with imazamox applied alone. Control by imazamox plus 2,4-D was similar to or greater than control by imazamox alone.

Field experiments were established on a loamy fine sand to evaluate weed control in a conservation tillage system where cotton was planted into sorghum stubble. Preemergence herbicides for Palmer amaranth and volunteer sorghum control in cotton included methazole, dipropetryn, prometryn, metolachlor, and metolachlor plus dipropetryn or prometryn. Dipropetryn controlled both weeds without crop injury. Above 1.7 kg ai/ha, methazole provided effective control but injured the crop. Prometryn was less effective than dipropetryn or methazole against Palmer amaranth and controlled <40% volunteer sorghum. Metolachlor unacceptably injured cotton. Cotton yields were excellent when both weeds were controlled.

Glyphosate-based, ready-to-use weed control products often contain pelargonic acid (PA) at a concentration equivalent to that of the glyphosate. It remains unclear what benefit, if any, this combination provides. Greenhouse experiments using large crabgrass, yellow nutsedge, longstalked phyllanthus, and prostrate spurge were conducted to determine whether the addition of PA improved weed control efficacy compared to glyphosate alone. Glyphosate was applied at a series of rates, ranging from 0.11 to 1.12 kg ae/ha, either alone or with an equal rate of PA. Addition of PA to glyphosate was synergistic only in longstalked phyllanthus and yellow nutsedge, and this synergism was manifested only as an increase in the amount of early (i.e., 5 to 7 d after treatment) visual injury. Conversely, longer-term control and control of regrowth was either not affected or reduced by the addition of PA. We conclude that the addition of PA to glyphosate in ready-to-use weed control products is neither warranted nor justified. However, we also note that the increase in early injury that was observed in only two of the four species evaluated could be an important attribute for the consumers for which these products are targeted.

Velvetleaf control and sugarbeet response to POST triflusulfuron applied alone and in combination with desmedipham plus phenmedipham, nonionic surfactant, and urea ammonium nitrate (50:50) were evaluated in the greenhouse (velvetleaf only) and field. In a second field study, the effect of POST applications of triflusulfuron, desmedipham plus phenmedipham, ethofumesate, endothall, or combinations of these herbicides on sugarbeet root yield and quality was determined in the absence of weeds. Triflusulfuron controlled velvetleaf only when nonionic surfactant (NIS) was added to the spray solution. Desmedipham plus phenmedipham plus triflusulfuron gave greater velvetleaf control than triflusulfuron in the absence of NIS in the field. However, adding desmedipham plus phenmedipham to triflusulfuron plus NIS decreased velvetleaf control in the greenhouse. Adding desmedipham plus phenmedipham to triflusulfuron plus NIS increased visible sugarbeet response compared to triflusulfuron plus nonionic surfactant or desmedipham plus phenmedipham 14 d after the last POST application in 1994. In the absence of weeds, POST herbicide applications that included triflusulfuron did not reduce sugarbeet root yield more than other POST herbicides.

The genus Bidens L. is in the Asteraceae (Compositae), the largest family of flowering plants, and one which contains many of the world's weed species. Beggarticks' phenomenal spread and colonization is due partly to their effective pollination mechanisms and their distinctive dispersal adaptations, which allow seed distribution by humans, animals, wind, and water.