Despite the abundance of common ragweed in crops and the potency of ragweed pollen as an allergen, pollen production in agricultural fields has hardly been evaluated. Our goal was to evaluate pollen and seed production of early- (i.e., plants missed by weed control) and late- (i.e., after weed control) emerging common ragweed growing in corn and soybean. Allocation and gender distribution were also evaluated. The experiment included 2 yr (2008, 2009), three competition treatments, two seeding/emergence dates, three densities, and four replicates. Competition treatments (main plots) included no crop or weeds (bare), corn, or soybean. Crops were glyphosate resistant. Subplots were seeded with common ragweed before or after glyphosate application at densities of 1 (4 m−2), 3 (12 m−2), or 6 (24 m−2) plants per plot. Ragweed plants were harvested in mid-October and measured (aboveground biomass, length of all male inflorescences, stem diameter, and seed production). Based on our estimates, mean (backtransformed from ln[x + 1]) pollen production values were: 6.25 (bare), 0.74 (corn), and 1.13 (soybean) × 108 pollen grains per ragweed. Biomass and diameter were good predictors of ragweed male and female fitness. Plant height was not correlated with maleness. In crops, ragweed gender distribution was shifted toward maleness. Estimations indicate early-emerging (June 18 to 23) ragweed produced three times more pollen than late (July 7 to 11) plants.

Field trials were conducted in 2009 and 2010 near Paterson, WA and Ontario, OR to evaluate weed control and potato tolerance to PRE-applied pyroxasulfone, saflufenacil, and KSU12800 herbicides. Pyroxasulfone at 0.09 to 0.15 kg ai ha−1 and saflufenacil at 0.05 to 0.07 kg ai ha−1 applied PRE alone or in tank mixes with several currently labeled herbicides did not injure potatoes at either site in both years. KSU12800 at 0.15 kg ai ha−1 injured potatoes from 18 to 26% for a period of about 4 wk after emergence at Ontario both years. In addition, KSU12800 at 0.29 and 0.45 kg ha−1 injured potatoes from 17 to 38% at 17 d after treatment (DAT) at Paterson in 2009. Pyroxasulfone at 0.15 kg ha−1 controlled barnyardgrass, hairy nightshade, and redroot pigweed 96% or greater, but control of common lambsquarters was variable. Saflufenacil at 0.07 kg ha−1 provided greater than 93% control of common lambsquarters, hairy nightshade, and redroot pigweed at both sites in 2010. KSU12800 at 0.15 kg ha−1 controlled common lambsquarters, hairy nightshade, and redroot pigweed 99% or more at Ontario, but only 87 to 93% at Paterson in 2010. These herbicides did not reduce yield of U.S. no. 1 tubers or total tuber yields compared to standard labeled herbicide treatments when weed control was adequate.

Field studies were conducted near College Station, TX, in 2006 and 2007 to evaluate the economic impact of common sunflower interference in field corn. A density of one common sunflower per 6 m of crop row caused a yield loss of 293 kg ha−1. Estimated losses at a net corn price of $0.08 kg−1 was $92 ha−1 for infestation levels of four common sunflower plants per 6 m of row. Corn yield was increased by 32 kg ha−1 by each 1,000 plant ha−1 increase in corn planting density. Corn planting densities of 49,400 and 59,300 plants ha−1 provided the greatest net returns with or without the presence of common sunflower competition. Corn yields were reduced by extended duration of sunflower competition, with losses exceeding 1,500 kg ha−1 per week and increasing in magnitude at a decreasing rate throughout the growing season. Herbicide treatments provided net returns of $600 to $1,300 ha−1 above no weed control in both 2006 and 2007. Net returns of $609 and $653 ha−1 were obtained without the use of any herbicide for sunflower control. Determining the economic impact of common sunflower interference in field corn allows producers to estimate the overall net return on the basis of duration of common sunflower interference and density, while considering varying net corn prices, crop planting density, and herbicide application costs.

The presence of weeds during bermudagrass putting green establishment can reduce growth and turf quality. Three field experiments were conducted in Georgia to investigate efficacy of dimethenamid, S-metolachlor, and oxadiazon on the establishment of ‘TifEagle’ bermudagrass from sprigs. Dimethenamid at 0.85 and 1.7 kg ai ha−1, S-metolachlor at 1.1 and 2.2 kg ai ha−1, and oxadiazon at 1.1, 2.2, and 4.4 kg ai ha−1 did not reduce bermudagrass cover from the untreated after 8 wk. S-metolachlor at 4.4 kg ha−1 was the only treatment that reduced sprig cover from the untreated after 12 wk. All S-metolachlor and oxadiazon treatments provided excellent (≥ 90%) green kyllinga control by 8 wk after treatment (WAT) while dimethenamid at 0.85, 1.7, and 3.4 kg ha−1 provided 78, 85, and 92% control, respectively. Dimethenamid treatments provided poor control (< 70%) of spotted spurge but fair control (70 to 79%) was achieved from S-metolachlor at 4.4 kg ha−1 and oxadiazon at 2.2 and 4.4 kg ha−1 by 8 WAT. Overall, low to middle rates of the herbicides tested appear to temporarily inhibit TifEagle bermudagrass sprig establishment but high rates of dimethenamid and S-metolachlor may reduce cover from the untreated.

Annual bluegrass is a troublesome weed in golf course putting greens. The objective of this research was to evaluate creeping bentgrass putting green tolerance to bispyribac-sodium tank-mixed with paclobutrazol in the transition zone. Field trials with four replications were conducted in Oklahoma during 2009 and 2010 and in Missouri during 2010. The results of this study suggest that tank-mixing bispyribac-sodium with paclobutrazol may discolor creeping bentgrass putting greens but will not reduce turf quality below acceptable levels. Normalized vegetative difference index readings indicated no treatment differences in turf greenness at 4 and 8 wk after initial treatment. Weekly application of bispyribac-sodium at 12.4 g ha−1 or biweekly application at 24.8 g ha−1 alone or with monthly applications of paclobutrazol at 224 g ha−1 did not cause unacceptable injury to creeping bentgrass putting greens during the spring.

Field dodder is a parasitic plant that attaches to the stems and leaves of broadleaf plants, including weeds, field crops, vegetables, and ornamentals, throughout most agricultural regions of the world. Effective field dodder control is extremely difficult to achieve, due to the nature of attachment and close association between host and parasite, which requires a highly effective and selective herbicide to destroy the parasite without crop damage. Previous studies have demonstrated the tolerance of certain tomato varieties to dodder parasitism. The aim of the present study was to evaluate the ability of sulfonylurea herbicides to control field dodder under greenhouse and field conditions. Two greenhouse studies and three field studies were conducted to evaluate the efficiency and crop selectivity of the sulfonylurea herbicides sulfosulfuron, rimsulfuron, halosulfuron, and flazasulfuron in controlling field dodder parasitizing tomato plants. Sulfosulfuron at 50 or 100 g ai ha−1 was effective and safe for tomato in field dodder control, while the other herbicides exhibited little or no dodder control.

Research was conducted to evaluate the weed suppression potential of ‘Rondo’ (4484-1693; PI 657830), a sister line (4484-1665), and other indica rice lines against barnyardgrass in field plots in Stuttgart, AR, using minimal herbicide inputs in two separate 3-yr experiments. Under weed pressure, Rondo and the sister line (4484-1665) generally produced yields that were comparable to those of weed-suppressive indica standards and approximately 50% greater than those of the least-suppressive commercial cultivars, such as ‘Kaybonnet’, ‘Katy’, and ‘Lemont’. Rice yield under weed pressure was correlated with weed-free yield and harvest height. Indica lines tended to produce more tillers than did the commercial cultivars. Tillering potential under weed-free conditions was not correlated with weed suppression or yield loss; however, tillering under weed pressure was strongly correlated with weed suppression and biomass, and yield and yield loss under the weed densities in these experiments. Rondo is presently being used for commercial organic rice production in Texas, in part due to its high yield potential and ability to suppress or tolerate rice pests, including weeds. Our results suggest that the weed-suppressive ability of Rondo and the other indica lines evaluated in these experiments is superior to that of many commercial cultivars.

Purple nutsedge response to various rates and timings of imazosulfuron was evaluated in 2007 and 2008 in Abilene, TX. Bermudagrass phytotoxicity never exceeded 4% throughout the duration of the trial and all bermudagrass recovered within 7 d of herbicide application. Imazosulfuron (0.56 kg ai ha−1) followed by (fb) imazosulfuron 1 wk after initial treatment (WAIT), imazosulfuron at 1.12 kg ai ha−1, and trifloxysulfuron at 0.03 kg ai ha−1 exhibited 94 to 96% control 4 WAIT. Imazosulfuron (0.56 kg ai ha−1) fb imazosulfuron 2, 3, and 4 WAIT exhibited 99% control 4 WAIT. Eight weeks later (12 WAIT), imazosulfuron (0.56 kg ai ha−1) fb imazosulfuron 3 WAIT controlled purple nutsedge 91%, whereas similar control (82 to 84%) was observed with a single application of trifloxysulfuron and imazosulfuron (0.56 kg ai ha−1) fb imazosulfuron 2 and 4 WAIT. A single application of imazosulfuron at 1.12 kg ai ha−1 and sequential treatment with imazosulfuron (0.56 kg ai ha−1) on a 1-wk interval only controlled purple nutsedge 51 to 69% 12 WAIT. Timing of sequential imazosulfuron application was identified as an important component of the purple nutsedge control program. Waiting 2, 3, or 4 WAIT for sequential imazosulfuron applications, rather than 1 WAIT, increased purple nutsedge control 31 to 40% 12 WAIT. The highest level of purple nutsedge control (91%) was observed with applications of imazosulfuron (0.56 kg ai ha−1) fb imazosulfuron 3 WAIT applied during midsummer. However, control with this treatment was statistically similar to control with a single application of trifloxysulfuron (82%).

Almost 1,650 corn, cotton, and soybean growers in 22 states participated in a 2010 telephone survey to determine their attitudes with regard to which weed species were most problematic in glyphosate-resistant (GR) crop production systems for corn, cotton, and soybean. The survey is a follow-up to a previous 2005 to 2006 survey that utilized a smaller set of growers from fewer states. In general, growers continued to estimate weed populations as low and few challenges have been created following adoption of GR cropping systems. Pigweed and foxtail species were dominant overall, whereas other species were more commodity and state specific. Corn, cotton, and soybean growers cited velvetleaf, annual morningglory, and waterhemp, respectively, as predominant weeds. Growers in the South region were more likely to report pigweed and waterhemp (Amaranthus spp.), whereas growers in the East and West reported horseweed. When growers were asked with which GR weeds they had experienced personally, horseweed was reported in all regions, but growers in the South more frequently reported pigweed, whereas growers in the East and West regions more frequently reported waterhemp. Comparisons with the previous 2005 survey indicated that more growers believed they were experiencing GR weeds and were more aware of specific examples in their state. In particular, the Amaranthus complex was of greatest concern in continuously cropped soybean and cotton.

Field studies were conducted in 2011 at the Malheur Experiment Station, Ontario, OR and Prosser, WA to evaluate the effect of simulated glyphosate drift on direct-seeded dry bulb onion. Glyphosate was applied at 8.6, 25.8, 86, 290, 434, and 860 g ae ha−1 when onion plants were at the flag-, two-, four-, and six-leaf stages. Onion foliar injury was directly related to the glyphosate dose and varied with application timing. Foliar injury at 7 d after treatment (DAT) ranged from 0 to 12% for glyphosate ≤ 25.8 g ha−1. Foliar injury increased at 21 DAT when glyphosate was applied ≥ 25.8 g ha−1 to plants at the flag- and four-leaf stage, and ranged from 24 to 99%. The 50%-injury glyphosate dose at 21 DAT was lowest when onion was treated at the four-leaf and flag stages and was estimated to be 76.8 and 81 g ha−1, respectively. Onion injury severity increased when glyphosate was applied at ≥ 86 g ha−1 and eventually resulted in plant death at 860 g ha−1. Foliar injury was inversely correlated to U.S. no. 1 onion yield. Onions displayed sensitivity to very low glyphosate doses especially at the four-leaf stage. Shikimic acid accumulation increased with the increase in glyphosate dose and was positively correlated with foliar injury and negatively correlated with plant height and onion yield.

Cleavers species (false cleavers and catchweed bedstraw) are among the top 10 most abundant weeds across the prairie region of western Canada, and are increasing in relative abundance at the fastest rate since the 1970s. In 2008, two false cleavers populations from Tisdale and Choiceland, Saskatchewan, were suspected of acetolactate synthase (ALS) –inhibitor resistance. Dose-response experiments were conducted with the use of imazethapyr and florasulam, both ALS inhibitors, as well as fluroxypyr, a synthetic auxin. Additionally, a 1,954–base-pair region of the ALS gene including sites known to confer ALS resistance were sequenced. Both populations were highly resistant to imazethapyr (resistance factors greater than 100), one population (Tisdale) was highly resistant to florasulam (Choiceland population susceptible, although a second, larger screening of 200 individuals indicated low frequency [2%] florasulam resistance), and both populations were susceptible to fluroxypyr. All sequenced Tisdale individuals screened with imazethapyr posessed the Trp574Leu mutation. In contrast, three point mutations were found for Choiceland individuals sequenced: Ser653Asn, Trp574Leu, and Asp376Glu. These ALS target-site mutations have not been documented previously in this species.

Farmers grow crops in the dryland region of the Pacific Northwest (PNW) using tillage practices ranging from moldboard plowing to no-tillage. The objective of this study was to determine the effect of tillage on persistence of imazamox herbicide in intermediate and high precipitation zones of the inland PNW. Along with a nontreated control, imazamox was applied to imidazolinone-tolerant winter wheat in the fall and spring at one, two, and three times the maximum labeled rate at locations near Genesee, ID, Davenport, WA, and Pendleton, OR. Moldboard plow, chisel plow, and no-till tillage treatments were implemented soon after wheat harvest and yellow mustard was planted the following season to determine crop response. Experiments were conducted at each location in 2005 to 2007 and 2006 to 2008. There were significant location by year and year and location interactions. There was no significant tillage by imazamox rate interaction, except at Pendleton in year 2, for all measured yellow mustard responses (crop injury, biomass, and yield). Genesee was colder than Pendleton and had more precipitation than Davenport, resulting in more injury to yellow mustard at Genesee than at Pendleton but less than at Davenport. Davenport had greater injury than the other two locations, likely due to lower soil pH, higher organic matter (OM), and cooler, drier climate, which allowed imazamox to persist longer in the soil. Overall, Pendleton had the least yellow mustard injury, which likely was related to its warmer, wetter climate and the concomitant rapid soil dissipation of imazamox. Tillage did not reduce the persistence of imazamox. Yellow mustard had the lowest injury and had greater mature biomass and seed yield in no-till seeded plots when averaged across imazamox rates compared to moldboard and chisel-plowed plots.

Wild buckwheat is the most abundant broadleaf weed across the Prairie region of western Canada. Acetolactate synthase (ALS)-inhibiting herbicides are commonly used to control this species and other broadleaf weeds in cereal crops. A field survey in Alberta in 2007 identified a single population that was putatively resistant to ALS-inhibiting herbicides. In herbicide resistance screening in the greenhouse, all F1 progeny tested were resistant to the ALS-inhibiting herbicides thifensulfuron/tribenuron, a sulfonylurea herbicide, or florasulam, a triazolopyrimidine herbicide; dose response of shoot biomass indicated the population was 10- and 20-fold less sensitive to thifensulfuron/tribenuron and florasulam, respectively, than a susceptible control population. ALS gene sequencing of 24 F1 progeny indicated that the Trp574Leu target-site mutation was responsible for conferring ALS-inhibitor resistance in this biotype, the first global report of ALS-inhibitor resistance for this species. Because this mutation typically endows high-level resistance across all five ALS-inhibitor classes, this wild buckwheat biotype may only be controlled by a different site-of-action herbicide.

Eight field studies were conducted over a 3-yr period from 2008 to 2010 in Ridgetown, Ontario, Canada, to determine the cumulative stress caused by simulated glyphosate spray drift followed by an in-crop application of metribuzin in processing tomato. As the simulated glyphosate spray drift rate increased so did the degree of injury to the tomatoes. At a simulated spray drift rate of 22.5 g ae ha−1 (2.5% of the recommended glyphosate field rate), a 23% decrease in red tomato yield was observed. Yield reductions increased to 88% of the control when 180 g ae ha−1 glyphosate (20% of the recommended field rate) was applied. Similarly when simulated spray drift rates were followed 3 to 5 d later with an in-crop application of metribuzin at 250 g ai ha−1, tomato yields decreased by 22 to 85% depending on glyphosate rate applied. A transient synergistic interaction was observed only when 22.5 g ae ha−1 glyphosate was followed by metribuzin. The synergistic response was no longer evident by the 28-d injury rating. Herbicide interactions were additive for crop injury, dry weight, fruit counts, and yield when glyphosate spray drift rates of 45, 90, or 180 g ae ha−1 were followed by metribuzin.

A 2010 survey of 1,299 corn, cotton, and soybean growers was conducted to determine their attitudes and awareness regarding glyphosate-resistant (GR) weeds and resultant implications on weed management practices. An additional 350 growers included in the current study participated in a 2005 survey, and these answers were compared across time so that cross-sectional and longitudinal comparisons of responses could be made. Most growers surveyed in 2010 were aware of the potential for weeds to evolve resistance to glyphosate; however, many growers were not aware of glyphosate resistance in specific weeds in their county or state. Growers in the South were different from growers in other geographic regions and were significantly more aware of local cases of GR weeds. Awareness of GR weeds did not increase appreciably from 2005 to 2010, but the percentage who reported GR weeds as problematic was significantly higher. Grower reports of GR weeds on-farm in 2010 were up considerably from 2005, with growers in the South reporting significantly more instances than growers in other regions. Growers in the South were also more likely to consider glyphosate resistance a serious problem. Overall, 30% of growers did not consider GR weeds to be a problem. It appears that most growers received information about glyphosate resistance from farm publications, although in the South this percentage was less than for other geographic regions. Growers in the South received more information from universities and extension sources.

Cultivation is a critical component of organic weed management and has relevance in conventional farming. Limitations with current cultivation tools include high costs, limited efficacy, and marginal applicability across a range of crops, soil types, soil moisture conditions, and weed growth stages. The objectives of this research were to compare the weed control potential of two novel tools, a block cultivator and a stirrup cultivator, with that of a conventional S-tine cultivator, and to evaluate crop response when each tool was used in pepper and broccoli. Block and stirrup cultivators were mounted on a toolbar with an S-tine sweep. In 2008, the tripart cultivator was tested in 20 independently replicated noncrop field events. Weed survival and reemergence data were collected from the cultivated area of each of the three tools. Environmental data were also collected. A multivariable model was created to assess the importance of cultivator design and environmental and operational variables on postcultivation weed survival. Additional trials in 2009 evaluated the yield response of pepper and broccoli to interrow cultivations with each tool. Cultivator design significantly influenced postcultivation weed survival (P < 0.0001). When weed survival was viewed collectively across all 20 cultivations, both novel cultivators significantly increased control. Relative to the S-tine sweep, the stirrup cultivator reduced weed survival by about one-third and the block cultivator reduced weed survival by greater than two-thirds. Of the 11 individually assessed environmental and operational parameters, 7 had significant implications for weed control with the sweep; 5 impacted control with the stirrup cultivator, and only 1 (surface weed cover at the time of cultivation) influenced control with the block cultivator. Crop response to each cultivator was identical. The block cultivator, because of its increased effectiveness and operational flexibility, has the potential to improve interrow mechanical weed management.

Approximately 1,300 growers from 22 states were surveyed during 2010 to determine herbicide use. Cropping systems included continuous glyphosate-resistant corn, cotton, and soybean, and various combinations of these crops and rotations with non–glyphosate-resistant crops. The most commonly used herbicide for both fall and spring applications was glyphosate followed by synthetic auxin herbicides. Herbicide application in spring was favored over application in the fall. The percentage of growers in a glyphosate-only system was as high as 69% for some cropping systems. Excluding glyphosate, the most frequently used herbicides included photosystem II, mitotic, and protoporphyrinogen oxidase inhibitors. A higher percentage of growers integrated herbicides other than glyphosate during 2010 compared with 2005. Extensive educational efforts have promoted resistance management by increasing the diversity of herbicides in glyphosate-resistant cropping systems. However, a considerable percentage of growers continued use of only glyphosate from the period of 2005 to 2010, and this practice most likely will continue to exert a high level of selection for evolved glyphosate-resistant weed species.

Organic growers need additional tools for weed control. A new technique using abrasive grit propelled by compressed air was tested in field plots. Grit derived from corncobs was directed at seedlings of summer annual weeds growing at the bases of corn plants when the corn was at differing early stages of leaf development. Season-long, in-row weed control exceeded 90% when two or three abrasion events were coupled with between-row cultivation. Timing of weed abrasion was critical, with highest levels of control corresponding to the one- and five-leaf stages or the one-, three-, and five-leaf stages of corn development. Corn yields associated with these treatments were equivalent to those of hand-weeded controls in which no abrasive grit was applied. Thus, air-propelled abrasive grit applications at the one-, three-, and five-leaf stages of corn controlled weeds sufficiently to prevent weed-induced reductions in corn grain. Additionally, these applications were not harmful to corn plants. This new concept for weed control may be of interest to organic crop managers.

Methyl bromide is a common fumigant for effective weed control in polyethylene-mulched vegetable crops. However, the ban on methyl bromide in the United States has created a need to find a suitable alternative. This study investigated the herbicidal efficacy of phenyl isothiocyanate (ITC) as a methyl bromide alternative for weed control in polyethylene-mulched bell pepper during 2006 and 2007. Six rates of phenyl ITC (0, 15, 75, 150, 750, 1,500 kg ha−1) under low-density polyethylene (LDPE) or virtually impermeable film (VIF) mulch were tested against yellow nutsedge, Palmer amaranth, and large crabgrass. Additionally, a standard treatment of methyl bromide/chloropicrin (67 : 33%) at 390 kg ha−1 under LDPE mulch was included for comparison. VIF mulch provided no advantage over LDPE mulch in either improving weed control or marketable yield in bell pepper. Unacceptable pepper injury (≥ 60%) occurred at the highest phenyl ITC rate of 1,500 kg ha−1 at 2 WATP in both years, regardless of mulch type. Higher bell pepper injury was observed in 2006 (≥ 36%) than in 2007 (≤ 11%) at 750 kg ha−1 of phenyl ITC. The lower injury in 2007 could be attributed to aeration of beds 48 h prior to transplanting. Regardless of mulch type, phenyl ITC at 2,071 (± 197) and 1,655 (± 309) kg ha−1 was required to control yellow nutsedge, Palmer amaranth, and large crabgrass equivalent to methyl bromide in 2006 and 2007, respectively. Bell pepper marketable yield at all rates of phenyl ITC was lower than methyl bromide in 2006. In contrast, marketable yield in phenyl ITC at 750–kg ha−1 was equivalent to methyl bromide in 2007. It is concluded that phenyl ITC should be applied at least 4.2 times higher rate than methyl bromide for effective weed control, and bed aeration is required to minimize crop injury and yield loss. Additional research is needed to test phenyl ITC in combination with other weed control strategies to obtain effective weed control with acceptable crop safety.

The nonnative biotype of common reed has invaded wetlands in many states including Nebraska, especially along the Platte River from Wyoming to the eastern edge of Nebraska. Therefore, three studies (disking followed by herbicide, mowing followed by herbicide, and herbicide followed by mechanical treatment) were conducted for 3 yr (2008 to 2010) at three locations in Nebraska. The objective was to evaluate common reed control along the Platte River using an integrated management approach based on herbicides (glyphosate or imazapyr), mowing, and disking, either applied alone or in combination. The level of weed control was determined by visual rating, percent flowering, and stem density. On the basis of visual rating, disking and mowing used alone provided common reed control for only a few months. However, the control was significantly prolonged (e.g., at least three seasons) when disking and mowing were combined with herbicide applications. Disking followed by herbicide and mowing followed by herbicide significantly reduced flowering and plant densities (P = 0.0001) compared to the untreated check. These results suggest that a combination of weed control methods has potential to control common reed.