Niger is a potential crop for the Northern Great Plains, but not until volunteer canola can be controlled. A study at Indian Head, SK, was conducted from 2007 to 2009 to determine the tolerance of niger to flucarbazone, a herbicide that controls volunteer canola. The tolerance was determined by applying three rates of flucarbazone (19, 28.5, and 38 g ai ha−1) at four application stages (two, four, six, and eight-leaf stage). Mean injury did not exceed 22% for any year by treatment combination. Injury was most prominent in 2007, and dissipated as the growing season progressed. Increasing the rate of flucarbazone increased crop injury depending on the year, application timing, and evaluation timing. Injury under 20% in 2007 and under 10% in 2008 and 2009 was observed at the start of flowering when flucarbazone was applied at the two, four, and six-leaf stage. Injury from applications at the two, four, and six-leaf stage decreased as the growing season progressed. When the labelled rate of flucarbazone for wheat (19 g ha−1) was applied at the two, four, or six leaf stage, injury was below 10%. Injury when flucarbazone was applied at the eight-leaf stage was highest during seed filling. Volunteer canola was controlled by flucarbazone. The application of flucarbazone relative to a weedy control increased yield by about 50% (138 to 213 kg ha−1) in 2008 and 2009. Flucarbazone rate did not affect niger yield except in 2007 where yield was about 100 kg ha−1 less with the two highest rates. Delaying flucarbazone application decreased niger yield, especially in the year (2007) with most niger injury. Flucarbazone application at the two- or four-leaf niger stage at a rate of 19 g ha−1 provided a good balance of weed control and crop tolerance.

Southern crabgrass is a common turfgrass weed throughout the United States, and in Florida a troublesome problem in St. Augustinegrass lawns. Because of herbicide label changes and lack of herbicide tolerance, no POST herbicides are currently registered for homeowner use for crabgrass control in residential and commercial St. Augustinegrass lawns. Alternative weed control methods, including cultural practices and unconventional herbicides, have been investigated to a limited extent for postemergence crabgrass control. In this study, alternative herbicides evaluated included 30% acetic acid, borax, sodium bicarbonate, and Garden Weasel AG Crabgrass Killer (sodium bicarbonate formulation including cinnamon, wheat and corn flour, and cumin). Treatments were applied to southern crabgrass at three growth stages (one to two leaf, three to four leaf, or one to two tiller). In the greenhouse, 30% acetic acid applied twice at 280 L ha−1 and two rates of AG Crabgrass Killer at 976 or 1,465 kg ha−1 provided ≥ 70% control of one to two–leaf southern crabgrass when evaluated 7 d after initial application (DAIA). No treatment provided > 70% control of three to four–leaf or one to two–tiller southern crabgrass or any size crabgrass beyond 7 DAIA. In field trials, no treatment provided acceptable (≥ 70%) southern crabgrass control at any weed stage. Initial turf injury was unacceptable for most rates of 30% acetic acid, sodium bicarbonate, and AG Crabgrass Killer, causing > 20% St. Augustinegrass injury 7 DAIA. By 21 DAIA, turf injury levels had fallen to ≤ 20% for most treatments. Because of high turfgrass injury and little residual control, alternative herbicides tested are not an effective substitute for using preemergence herbicides for southern crabgrass control. If other options are not available, they may have a role as a limited spot treatment in St. Augustinegrass.

Field experiments were conducted at the North Central Agricultural Research Station in Fremont, OH, in 2006 and 2007, to evaluate tolerance of banana pepper to S-metolachlor and clomazone, and the efficacy of these herbicides on green and giant foxtail, common lambsquarters, and common purslane. The crop was machine-transplanted in late spring of each year. Pretransplant (PRETP) herbicide treatments included two S-metolachlor rates (534 and 1,070 g ai ha−1), two clomazone rates (560 and 1,120 g ai ha−1), and four tank mixes of S-metolachlor plus clomazone (534 + 560 g ha−1, 1,070 + 560 g ha−1, 534 + 1,120 g ha−1, and 1,070 + 1,120 g ha−1). Crop injury and weed control data were collected at 2 and 4 wk after treatment (WAT). The crop was harvested two times from August to September. Minor crop injury was observed at 2 WAT only in 2006 and in plots treated with S-metolachlor, alone or in combination with clomazone. In 2007, slight crop injury at 6 WAT in most herbicide-treated plots was mostly related to weeds that grew regardless of herbicide treatment. In general, S-metolachlor provided less weed control than did clomazone or tank mixes of S-metolachlor plus clomazone. Clomazone did not reduce yield of banana pepper. Registration of clomazone would provide banana pepper growers an opportunity to control weeds caused by late emergence or poor initial control following a burndown herbicide application.

Glasshouse research was conducted to investigate the efficacy of herbicide safeners for improving creeping bentgrass (CBG) tolerance to various herbicides. CBG injury from amicarbazone (150 g ha−1), bispyribac-sodium (110 g ha−1), fenoxaprop-p-ethyl (35 g ha−1), imazapic (45 g ha−1), quinclorac (1,050 g ha−1), or topramezone (37 g ha−1) applied in combination with the herbicide safeners naphthalic anhydride or isoxadifen-ethyl was evaluated. These safeners reduced CBG injury from topramezone only. Topramezone was then applied in combination with naphthalic anhydride, isoxadifen-ethyl, cloquintocet-mexyl (cloquintocet), fenchlorazole-ethyl, mefenpyr-diethyl, and benoxacor. These experiments determined that CBG injury was lowest from topramezone in combination with cloquintocet. Additional experiments evaluated topramezone (37 g ha−1) with several rates of cloquintocet and determined that applications at ≥ 28 g ha−1 reduced CBG injury similarly. Cloquintocet (28 g ha−1) increased topramezone I50 values against CBG, but not large crabgrass or goosegrass. The cytochrome P450 (cP450) inhibitor malathion (1000 g ha−1) reduced topramezone I50 values against CBG in one experimental run. Topramezone–cloquintocet combinations warrant further research in field settings.

Flumioxazin is a protoporphyrinogen oxidase inhibitor with potential for POST annual bluegrass control and PRE smooth crabgrass control in bermudagrass. However, flumioxazin applications are often less effective in winter, compared with fall, because of reduced efficacy on mature annual bluegrass. The objective of this research was to evaluate tank-mixtures of flumioxazin with six other herbicide mechanisms of action for POST annual bluegrass control in late winter and residual smooth crabgrass control. Flumioxazin at 0 or 0.42 kg ai ha−1 was evaluated in combination with flazasulfuron at 0.05 kg ai ha−1, glufosinate at 1.26 kg ai ha−1, glyphosate at 0.42 kg ae ha−1, mesotrione at 0.28 kg ai ha−1, pronamide at 1.68 kg ai ha−1, or simazine at 1.12 kg ai ha−1. Flumioxazin alone controlled annual bluegrass 61 to 70% at 8 wk after treatment (WAT) in three experiments from 2012 to 2014 in central Georgia. Flumioxazin tank-mixed with flazasulfuron, glyphosate, glufosinate, pronamide, and simazine provided good (80 to 89%) to excellent (> 90%) control of annual bluegrass at 8 WAT in 2 of 3 yr. These tank-mixtures were also more effective than flumioxazin alone in 2 of 3 yr, and control was greater or equal to the tank-mix partners applied alone. Treatments that included flumioxazin provided excellent (≥ 90%) control of smooth crabgrass at 6 mo after treatment in all 3 yr. Overall, tank-mixing flumioxazin with other herbicide chemistries may improve POST annual bluegrass control, compared with exclusive treatments, and effectively control smooth crabgrass in bermudagrass.

Smutgrass, a native of tropical Asia, is a perennial weed that affects many improved perennial grass pastures in Florida and throughout the southeastern United States. The two varieties of smutgrass predominant in Florida are small smutgrass and giant smutgrass. Three field experiments were conducted from 2008 to 2012 to evaluate the effect of integrated long-term management strategies using both cultural and herbicide inputs for giant smutgrass control in bahiagrass pastures. Burning did not have a significant impact on long-term control. In 2011, no differences were observed when hexazinone was integrated with tillage or hexazinone was combined with supplemental nitrogen compared with sequential or single applications of hexazinone. However, cultural treatments that preceded hexazinone application compared with those that received two sequential applications of hexazinone had lower smutgrass control 36 mo after treatment. Data indicate that a sequential application of hexazinone may be better than implementing tillage. Sequential hexazinone applications, when applied at 0.56 kg ai ha−1 or greater, resulted in similar or increased control as compared with single applications. Collectively, these data suggest that sequential applications of hexazinone may be most effective for smutgrass management, and cultural techniques, including tillage, should be followed by hexazinone application the following year.

Two field experiments were conducted during 2012 and 2013 at Roseworthy, South Australia to identify effective herbicide options for the management of clethodim-resistant rigid ryegrass in faba bean. Dose–response experiments confirmed resistance in both field populations (B3, 2012 and E2, 2013) to clethodim and butroxydim. Sequencing of the target site of acetyl coenzyme A carboxylase gene in both populations identified an aspartate-2078-glycine mutation. Although resistance of B3 and E2 populations to clethodim was similar (16.5- and 21.4-fold more resistant than the susceptible control SLR4), the B3 population was much more resistant to butroxydim (7.13-fold) than E2 (2.24-fold). Addition of butroxydim to clethodim reduced rigid ryegrass plant density 60 to 80% and seed production 71 to 88% compared with the standard grower practice of simazine PPI plus clethodim POST. Clethodim + butroxydim combination had the highest grain yield of faba bean (980 to 2,400 kg ha−1). Although propyzamide and pyroxasulfone plus triallate PPI provided the next highest levels of rigid ryegrass control (< 60%), these treatments were more variable and unable to reduce seed production (6,354 to 13,570 seeds m−2) to levels acceptable for continuous cropping systems.

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.

The occurrence of 36 arable weed species across 13 counties in the eastern Arkansas–Mississippi Delta area on 489 randomly selected road sites was surveyed in 2012. Palmer amaranth, johnsongrass, large crabgrass, barnyardgrass, prickly sida, and broadleaf signalgrass were the top six weed species, with occurrence noted at 313, 294, 261, 238, 176, and 136 sites, respectively. Factors found to affect weed occurrence along Mississippi Delta roadsides included topographical characteristics, weed species, ditch slope, road type, and nearby land use. Among roadside topographical characteristics, road shoulder was found to strongly affect weed occurrence. In addition, paved and gravel road types with moderate roadside slope explained most of the variability of weed occurrence at each sampling site. Additionally, nearby arable land use affected weed occurrence more so than natural, residential, and pastoral land. Barnyardgrass, johnsongrass, and Palmer amaranth were 3.6 to 4.3 times more likely to occur than all other species identified. An effective weed management plan along eastern Arkansas–Mississippi Delta roadsides should focus on road shoulder, adjacent arable land use, road type, and specific weed species (e.g., Palmer amaranth, johnsongrass, and barnyardgrass). The inclusion of these parameters in future weed control programs can prove invaluable for preventing the spread of the herbicide-resistant Palmer amaranth, barnyardgrass, and johnsongrass.

Fluridone has been used to successfully manage Eurasian watermilfoil since the late 1980s. However, recent documentation of hybrid watermilfoils and the resulting potential for reduced herbicide sensitivity necessitate the need for an assay to determine individual population response to fluridone. A known fluridone-resistant hybrid watermilfoil population from Townline Lake in Michigan was compared to 11 Eurasian and hybrid watermilfoil populations in laboratory experiments to develop a method for determining response to fluridone. Apical shoot tips were exposed to increasing concentrations of fluridone (0 to 48 μg L−1) for 3, 5, and 7 d. Chlorophyll fluorescence (Fv/Fm) was evaluated using a pulse-amplitude modulated fluorometer at each interval along with pigment analysis of chlorophyll and β-carotene at the 7-d interval. Fv/Fm and pigment analysis yielded the same results. A fluridone concentration of 12 μg L−1 and an analysis interval of 7 d were found to be optimal in determining invasive watermilfoil response to fluridone. Use of such small-scale assays can provide resource managers a rapid tool to cost-effectively evaluate invasive watermilfoil response to fluridone.

POST weed control in soybean in the United States is difficult because weed resistance to herbicides has become more prominent. Herbicide applicators have grown accustomed to low carrier volume rates that are typical with glyphosate applications. These low carrier volumes are efficient for glyphosate applications and allow applicators to treat a large number of hectares in a timely manner. Alternative modes of action can require greater carrier volumes to effectively control weeds. Glyphosate, glufosinate, lactofen, fluazifop-P, and 2,4-D were evaluated in field and greenhouse studies using 47, 70, 94, 140, 187, and 281 L ha−1 carrier volumes. Spray droplet size spectra for each herbicide and carrier volume combination were also measured and used to determine their impact on herbicide efficacy. Glyphosate efficacy was maximized using 70 to 94 L ha−1 carrier volumes using droplets classified as medium. Glufosinate efficacy was maximized at 140 L ha−1 and decreased as droplet diameter decreased. For 2,4-D applications, efficacy increased when using carrier volumes equal to or greater than 94 L ha−1. Lactofen was most responsive to changes in carrier volume and performed best when applied in carrier volumes of at least 187 L ha−1. Carrier volume had little impact on fluazifop-P efficacy in this study and efficacy decreased when used on taller plants. Based on these data, applicators should use greater carrier volumes when using contact herbicides in order to maximize herbicide efficacy.

Drip-applied herbicides provide farmers with a more timely and cost-effective approach for applying PRE herbicides; however, herbicide movement is often limited. Field studies were conducted evaluating drip-application methods for applying PRE herbicides under polyethylene-mulched beds on yellow nutsedge punctures and the corresponding responses of a tomato crop (height and yield). The experiment was a factorial treatment arrangement of three drip application methods and three PRE-applied herbicides [halosulfuron (54 g ai ha−1), S-metolachlor (1.4 kg ha−1), and fomesafen (280 g ha−1)]. Herbicides were applied either immediately following saturation of the planting beds (method A), over an extended period while saturating the beds (method B), or prior to bed saturation (method C). Additional treatments included a commercial standard (S-metolachlor sprayed to the bed surface prior to mulch application) and a nontreated control (polyethylene mulch only). Drip-applied fomesafen, halosulfuron, and S-metolachlor provided similar control of yellow nutsedge, produced comparable yields, and failed to elicit any negative growth responses when compared to our commercial standard. With the exception of nutsedge punctures counted 56 DAT, application method did not influenced measurable outcomes. At 56 DAT nutsedge punctures were significantly lower in treatments applied by method B compared to those applied with method A.