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

The herbicide 2,4-D is used in a variety of cropping systems, especially in grasses because it is a selective postemergence broadleaf herbicide. However, the most common formulation (2,4-D dimethylamine) is antagonized when mixed in hard water. The objective of this research was to determine which formulations of 2,4-D or premixes of various formulations of synthetic auxin herbicides are subject to hard water antagonism. Formulations surveyed for hard water antagonism in the first experiment included 2,4-D dimethylamine, 2,4-D diethanolamine, 2,4-D monomethylamine, 2,4-D isopropylamine salt, 2,4-D choline salt, 2,4-D isooctyl ester, and 2,4-D ethylhexyl ester. Synthetic auxin formulation types in the second experiment included water-soluble, emulsifiable concentrates and emulsion-in-water. All formulations were mixed with both soft and hard water (600 mg CaCO3 L−1) and applied to dandelions to determine whether antagonism occurred in hard water. Water-soluble (amine and choline) 2,4-D formulations were antagonized by hard water, but water-insoluble (ester) 2,4-D formulations were not antagonized. Similar results were found by formulation type with water-soluble synthetic auxin premixes antagonized but emulsifiable concentrates not antagonized. Furthermore, water-soluble salt formulations were not antagonized when formulated in premixes with other synthetic auxin herbicides as an emulsion-in-water. This research demonstrates that all 2,4-D water-soluble formulations and water-soluble premixes with phenoxycarboxylic acid herbicides are subject to hard water antagonism. Formulations of 2,4-D containing emulsifying agents protect against antagonism by the water-insoluble nature of ingredients in their formulation.

Common blue violet is a widely distributed, perennial broadleaf that is difficult to control in lawns. Two experiments were conducted to evaluate the efficacy of synthetic auxin herbicides and their mixtures or rate for common blue violet control. A herbicide comparison experiment was conducted with treatments including a nontreated check; 2,4-D dimethylamine; 2,4-D isooctyl ester (2,4-D ester); dichlorprop (2,4-DP) ethylhexyl ester, MCPA dimethylamine; mecoprop dimethylamine; triclopyr butoxyethyl ester; quinclorac; and mixtures of triclopyr + quinclorac; 2,4-D ester + 2,4-DP; 2,4-D ester + triclopyr; 2,4-D ester + 2,4-DP + triclopyr. All herbicides were applied at 1.12 kg ae ha–1 except quinclorac (0.84 kg ha–1). Additionally, a triclopyr dose-response experiment was conducted using rates of 0, 0.14, 0.28, 0.56, 0.84, and 1.12 kg ha–1. Epinasty ranged from 80% to 99% at 21 d after application for triclopyr-containing treatments and no more than 28% for all other treatments. Plant mass from harvest and regrowth data from the comparison experiment indicated triclopyr-containing treatments provided the highest common blue violet control. Mixtures containing triclopyr did not differ from triclopyr alone, indicating there was no added effect between herbicide mixtures. The triclopyr dose-response experiment confirmed triclopyr efficacy across data collection types. As triclopyr dose increased, violet epinasty increased and chlorophyll content and dry weight decreased. Triclopyr applied at 0.81 kg ha–1 or greater concentration provided 75% or greater control, as indicated by regrowth data. Many herbicides containing triclopyr are registered for use in turf, but most apply a concentration not greater than 0.56 kg ha–1 triclopyr when applied at the high label rate. Thus, to achieve good (75%) common blue violet control, turf managers should select products that contain triclopyr and apply doses of at least 0.81 kg ha–1 when used according to the label.Nomenclature: 2, 4-dichlorophenoxyacetic acid; (±)-2-(4-chloro-2-methylphenoxy)propanoic acid (mecoprop); (±)-2-(2, 4-dichlorophenoxy) propanoic acid (dichlorprop); 2, 4-D dimethylamine; 2, 4-D isooctyl ester; 4-chloro-2-methylphenoxyacetic acid; 3, 7-dichloro-8-quinolinecarboxylic acid (quinclorac); 3, 5, 6-trichloro-2-pyridinyloxyacetic acid (triclopyr); common blue violet; Viola sororia Willd. VIOPP.

Horseweed is a competitive summer or winter annual weed that produces up to 230,000 small seeds per plant that are capable of traveling more than 500 km via wind. Giant ragweed is a tall, highly competitive summer annual weed. Glyphosate-resistant (GR) horseweed and GR giant ragweed pose significant challenges for producers in the United States and Ontario, Canada. It is thought that an integrated weed management (IWM) system involving herbicide rotation is required to control GR biotypes. Halauxifen-methyl is a new selective broadleaf POST herbicide registered for use in cereal crops; there is limited information on its efficacy on horseweed and giant ragweed. The purpose of this research was to determine the efficacy of halauxifen-methyl applied POST, alone and in a tank mix, for the control of GR horseweed and GR giant ragweed in wheat across southwestern Ontario. For each weed species, an efficacy study consisting of six field experiments was conducted over a 2-yr period (2018, 2019). At 8 wk after application (WAA), halauxifen-methyl, fluroxypyr/halauxifen-methyl, fluroxypyr/halauxifen-methyl + MCPA EHE, fluroxypyr + MCPA ester, 2,4-D ester, clopyralid, and pyrasulfotole/bromoxynil + ammonium sulfate controlled GR horseweed >95%. Fluroxypyr and MCPA provided only 86% and 37% control of GR horseweed, respectively. At 8 WAA, fluroxypyr, fluroxypyr/halauxifen-methyl, fluroxypyr/halauxifen-methyl + MCPA EHE, fluroxypyr + MCPA ester, fluroxypyr/halauxifen-methyl + MCPA EHE + pyroxsulam, 2,4-D ester, clopyralid, and thifensulfuron/tribenuron + fluroxypyr + MCPA ester controlled GR giant ragweed 87%, 88%, 90%, 94%, 96%, 96%, 98%, and 93%, respectively. Halauxifen-methyl and pyroxsulam provided only 45% and 28% control of GR giant ragweed, respectively. Halauxifen-methyl applied alone POST in the spring controlled GR horseweed but not GR giant ragweed in winter wheat.

The adoption of chemical fallow rotations in Pacific Northwest dryland winter wheat production has caused a weed species composition shift in which scouringrush has established in production fields. Thus, there has been interest in identifying herbicides that effectively control scouringrush in winter wheat–chemical fallow cropping systems. Field experiments were established in growers’ fields near Reardan, WA, in 2014, and The Dalles, OR, in 2015. Ten herbicide treatments were applied to mowed and nonmowed plots during chemical fallow rotations. Scouringrush stem densities were quantified the following spring and after wheat harvest at both locations. Chlorsulfuron plus MCPA-ester resulted in nearly 100% control of scouringrush through wheat harvest. Before herbicide application, mowing had no effect on herbicide efficacy. We conclude chlorsulfuron plus MCPA-ester is a commercially acceptable treatment for smooth and intermediate scouringrush control in winter wheat–chemical fallow cropping systems; however, the lack of a positive yield response when scouringrushes were controlled should factor into management decisions.

Flax yield can be severely reduced by weeds. The combination of limited herbicide options and the spread of herbicide-resistant weeds across the prairies has resulted in a need for more weed control options for flax producers. The objective of this research was to evaluate the tolerance of flax to topramezone, pyroxasulfone, flumioxazin, and fluthiacet-methyl applied alone as well as in a mix with currently registered herbicides. These herbicides were applied alone and in mixtures at the 1X and 2X rates and compared with three industry standards and one nontreated control. This experiment was conducted at Carman, MB, and Saskatoon, SK, as a randomized complete block with four replications. Data were collected for crop population, crop height, yield, and thousand-seed weight. Ratings for crop damage (phytotoxicity) were also taken at three separate time intervals: 7 to 14, 21 to 28, and 56+ d after treatment. Crop tolerance to these herbicides varied between site-years. This was largely attributed to differences in spring moisture conditions and the differences in soil characteristics between sites. Herbicide injury was transient. Hence, no herbicide or combination of herbicides significantly impacted crop yield consistently. Flumioxazin was the least promising herbicide evaluated, as it caused severe crop damage (>90%) when conditions were conducive. Overall, flax had excellent tolerance to fluthiacet-methyl, pyroxasulfone, and topramezone. Flax had excellent crop safety to the combination of pyroxasulfone + sulfentrazone. However, mixing fluthiacet-methyl and topramezone with MCPA and bromoxynil, respectively, increased crop damage and would not be recommended.

Five experiments were conducted over a 2-yr period (2013 and 2014) to evaluate POST herbicides in winter wheat fields with a history of glyphosate-resistant (GR) horseweed. Control 4 wk after treatment (WAT) with pyrasulfotole + bromoxynil was 95%. Control 8 WAT with 2,4-D, dicamba + MCPA + mecoprop, clopyralid, and pyrasulfotole + bromoxynil ranged from 89 to 97%; these herbicides also reduced GR horseweed density and biomass by 97 to 99%. Single mode of action herbicides like 2,4-D controlled GR horseweed; however, multiple modes of action should be used to prevent populations from becoming incrementally more resistant under repeated selection pressure. Nomenclature: Glyphosate; horseweed, Conyza canadensis (L.) Cronq.; winter wheat, Triticum aestivum L.

Herbicide-resistant kochia is an increasing concern for growers in the northwestern United States. Four suspected glyphosate-resistant (Gly-R) kochia accessions (referred to as GIL01, JOP01, CHES01, and CHES02) collected in fall 2012 from four different chemical-fallow fields in northern Montana were evaluated. The objectives were to confirm and characterize the level of glyphosate resistance in kochia accessions relative to a glyphosate-susceptible (Gly-S) accession and evaluate the effectiveness of various POST herbicides for Gly-R kochia control. Whole-plant dose–response experiments indicated that the four Gly-R kochia accessions had 7.1- to 11-fold levels of resistance relative to the Gly-S accession on the basis of percent control ratings (I50values). On the basis of shoot dry weight response (GR50values), the four Gly-R kochia accessions exhibited resistance index (R/S) ratios ranging from 4.6 to 8.1. In a separate study, the two tested Gly-R accessions (GIL01 and JOP01) showed differential response (control and shoot dry weight reduction) to various POST herbicides 21 d after application (DAA). Paraquat, paraquat + linuron, carfentrazone + 2,4-D, saflufenacil alone or with 2,4-D, and bromoxynil + fluroxypyr effectively controlled (99 to 100%) and reduced shoot dry weight (88 to 92%) of the GIL01 accession, consistent with the Gly-S kochia accession; however, bromoxynil + MCPA and bromoxynil + pyrasulfotole provided 76% control and 83% shoot dry weight reduction of the GIL01 accession and were lower compared with the Gly-S accession. The JOP01 accession exhibited lower control or shoot dry weight reduction to all herbicides tested, except dicamba, diflufenzopyr + dicamba + 2,4-D, paraquat + linuron, and bromoxynil + pyrasulfotole, compared with the Gly-S or GIL01 population. Furthermore, paraquat + linuron was the only treatment with ≥ 90% control and shoot dry weight reduction of the JOP01 kochia plants. Among all POST herbicides tested, glufosinate was the least effective on kochia. This research confirms the first evolution of Gly-R kochia in Montana. Future research will investigate the mechanism of glyphosate resistance, inheritance, ecological fitness, and alternative strategies for management of Gly-R kochia.

Field studies were conducted to evaluate POST herbicides with adjuvants for the control of three-cornered jack in winter wheat. The herbicides evaluated were fluroxypyr 9.7% w/w + MCPA 38.8% w/w (formulated mixture [450 g ai ha−1]), carfentrazone-ethyl (20 g ai ha−1), bromoxynil 26.8% w/w + MCPA 40.0% w/w (formulated mixture [450 g ai ha−1]), thifensulfuron-methyl (75 g ai ha−1), and tribenuron-methyl (75 g ai ha−1), applied alone or tank mixed with the adjuvants alkyl ether sulfate sodium salt (625 mL ha−1) or fatty alcohol ethoxylate (375 mL ha−1). The addition of adjuvants to carfentrazone-ethyl resulted in > 94% control of three-cornered jack. Both adjuvants enhanced the efficacy of all herbicides for control of three-cornered jack, except thifensulfuron-methyl. However, a maximum increase in phytotoxicity on three-cornered jack was achieved with the addition of either adjuvant to tribenuron-methyl compared with herbicides used alone. Bromoxynil + MCPA and carfentrazone-ethyl gave maximum wheat yield and yield components.

Dry-seeded rice systems are an emerging production technology in many Asian countries. A field study was conducted in 2011 and 2012 at the farm of the Rice Research and Development Institute, Batalagoda, Sri Lanka, to evaluate the performance of different herbicides in a dry-seeded rice system. Weed control treatments were nontreated (weedy), pretilachlor plus pyribenzoxim, cyhalofop-butyl, thiobencarb plus propanil, propanil, and bispyribac-sodium plus metamifop. All these POST herbicides were applied at 8 d after sowing, followed by an MCPA spray at 20 d after sowing. The dominant weeds in the study were barnyardgrass, Chinese sprangletop, and knotgrass. All herbicide treatments provided similar weed control, which ranged from 82 to 99%. Weeds in the nontreated plots reduced rice grain yield by 58 to 79% compared with the herbicide-treated plots. All herbicide-treated plots, except cyhalofop-butyl-treated ones, produced similar grain yield, which ranged from 3.7 to 4.2 t ha−1 in 2011 and from 6.0 to 7.0 t ha−1 in 2012. The results of our study suggest that different herbicides provided similar weed control and therefore different herbicides can be rotated in different seasons to reduce selection pressure on weeds.

Clovers are commonly included as utility plants within mixed grass swards, such as pastures and roadside right-of-ways. As such, they provide supplemental nitrogen, quality forage, and insect habitat. Yet weed control within mixed swards is often hampered by the lack of selective herbicides that are tolerated by clovers. Differential tolerance of legumes to common row-crop and pasture herbicides has previously been reported, yet little information is available that is specific to clover species. Herbicide injury of clover is often inconsistent, hypothetically due to differential species tolerance. Field and greenhouse experiments were conducted with the objective of testing differential tolerance amongst four clover species. Our experiments suggest varying tolerances amongst clover species and common broadleaf herbicides. Only imazaquin control differed due to species; however, treatment by clover interactions were further demonstrated due to variable reductions in clover height. Imazaquin, 2,4-D, 2,4-DB, and triclopyr height reductions differed due to clover species. Differential clover response to herbicide treatment should be an important consideration when managing mixed grass–clover swards and should be accounted for in future research. On a more practical level, our experiments demonstrate a range of herbicides that effectively control clover species, including atrazine, dicamba, clopyralid, 2,4-D, triclopyr, metsulfuron, and trifloxysulfuron. However, results suggest that 2,4-DB, imazethapyr, and bentazon are candidate herbicides for weed control in scenarios in which clover is a desirable crop.

Field studies were conducted to evaluate Italian ryegrass control and winter wheat tolerance to applications of diclofop, mesosulfuron plus methylated seed oil (MSO) alone or with 30% urea ammonium nitrate (UAN), mesosulfuron plus thifensulfuron plus tribenuron plus MSO, mesosulfuron plus MCPA plus MSO, or flufenacet plus metribuzin. Treatments were applied to wheat PRE, two- to three-leaf wheat (2–3 LF) at Feekes stage 1.0 or to one- to two-tiller wheat (TILL) at Feekes stage 3.0, depending on label recommendations. Studies were conducted in Williamson, GA, and Plains, GA, from autumn 2003 to spring 2005. Italian ryegrass control was variable, depending on location and year. Maximum and most-consistent Italian ryegrass control (> 90%) occurred with mesosulfuron plus MSO and UAN. Without UAN, control of Italian ryegrass with mesosulfuron varied from 44 to 97%. That variability was partially attributed to unfavorable environmental conditions associated with cold night time temperatures at or below 0 C, following applications. Wheat injury observed in response to herbicide treatments was minimal (< 15%) and transient; wheat recovered with no differences in yield.

Field, greenhouse, and laboratory studies were conducted to determine the effect of MCPA ester, fertilizer type, and fertilizer rate on feral rye control with imazamox. In field studies near Sidney, NE, increasing the concentration of liquid ammonium phosphate (10–34–0) from 2.5 to 50% of the spray solution decreased feral rye control with imazamox by as much as 73%. Conversely, adding MCPA ester to imazamox significantly increased feral rye control in field studies by up to 77%. Initial greenhouse studies confirmed the liquid ammonium phosphate antagonism effect, but subsequent greenhouse studies were inconsistent with regard to the interaction between fertilizer and imazamox. At least one source of liquid ammonium phosphate was shown not to be antagonistic, and therefore fertilizer source or contaminants may be responsible for initial field observations. Greenhouse studies confirmed the synergistic interaction between MCPA and imazamox. MCPA ester applied at 560 g ai ha−1 decreased the rate of imazamox required to cause 50% reduction in feral rye dry weight (GR50) to 13 g ha−1 compared to 35 g ha−1 for imazamox alone. Although addition of MCPA ester increased 14C-imazamox absorption by 8% in laboratory studies, less 14C translocated out of the treated leaf; therefore the mechanism of synergism does not appear to be related to imazamox absorption or translocation.

Triticale is a low input crop, produced in North America primarily for silage for animal feed. Currently, seed growers have few herbicide options for producing certified seed. There is anecdotal evidence that triticale tolerates many of the same herbicides as wheat. In 2004 and 2005, the tolerance of three spring triticale varieties (AC Alta, AC Ultima, and Pronghorn) was tested with four herbicides registered for wheat: florasulam + MCPA ester, clodinafop-propargyl, thifensulfuron-methyl/tribenuron-methyl, and sulfosulfuron-methyl + 2,4-D ester. Herbicides were applied at the label rate (1×) for wheat and twice (2×) that rate. Crop injury, plant height, biomass, and seed yields were quantified. Neither florasulam + MCPA ester, clodinafop-propargyl, nor thifensulfuron-methyl/tribenuron-methyl at 1× or 2× use rates significantly injured triticale. Sulfosulfuron-methyl + 2,4-D ester reduced triticale height at the 1× and 2× rates, as well as reduced biomass and yield at the 2× rate. Florasulam + MCPA ester, clodinafop-propargyl, and thifensulfuron-methyl/tribenuron-methyl do not cause significant crop injury and can be used for weed control in spring triticale, but sulfosulfuron-methyl + 2,4-D ester is not recommended for use in triticale.

Flaxleaf fleabane is a difficult-to-control weed in dryland minimum tillage farming systems in the northeast grains region of Australia. Experiments were conducted between 2003 and 2005 to identify effective control strategies on flaxleaf fleabane in wheat and sorghum. A preplant application of chlorsulfuron at 15 g ai/ha in wheat controlled flaxleaf fleabane ≥ 90%. The efficacy of early postemergent applications of metsulfuron–methyl at 4.2 g ai/ha varied between years. However, the flaxleaf fleabane was controlled > 85% with metsulfuron–methyl at 4.2 g ai/ha plus MCPA at 420 g ae/ha plus picloram at 26 g ae/ha, or metsulfuron–methyl followed by late postemergent 2,4-D amine at 300 g ae/ha. In sorghum, a preplant application of glyphosate at 900 g ae/ha plus 2,4-D amine at 900 g ae/ha or dicamba at 500 g ae/ha at 1 mo before sorghum planting provided ≥ 95% control. Preplant atrazine at 2,000 g ai/ha controlled flaxleaf fleabane 83 to 100% in sorghum. At-planting atrazine at 2,000 or 1,000 g ai/ha can be applied to control new emergence of flaxleaf fleabane and grasses, depending on the weed pressure and spectrum. Flaxleaf fleabane reduced sorghum yield 65 to 98% if not controlled.

When solid stands of foxtail millet are cut for swath grazing, the grazing season for cattle is extended and winter feeding costs reduced. The economic success of this practice depends on inexpensive weed control. Eight single- and double-rate herbicide combinations (g ai/ha) were evaluated and compared to a weed-free check: MCPA + bromoxynil (280 + 280 or 560 + 560); MCPA + clopyralid (560 + 100 or 1120 + 200); MCPA + fluroxypyr (562 + 108 or 1124 + 216); and MCPA + clopyralid + fluroxypyr (560 + 100 + 144 or 1120 + 200 + 288). This study was conducted at Indian Head, Saskatchewan (SK) in 2004, 2005, 2006, and 2007 and at Scott, SK, in 2006 and 2007. Crop injury and dry matter yield were measured. Results of the study indicate that crop injury exceeded 20% at only one out of six sites at 7 to 14 d after herbicide treatment. Double-rate MCPA + bromoxynil treatments had higher injury ratings than the weed-free check 7 to 14 d after treatment in all site years. As the growing season progressed, injury ratings tended to decline except at Scott in 2007, where injury ratings at the 21 to 35 d period were numerically greater than the other two rating periods. There were no differences among treatments for crop biomass production. We conclude that all four herbicide combinations at the labeled rate are safe to use on foxtail millet in Saskatchewan, and probably in other areas with similar environmental growing conditions.

Experiments were conducted to evaluate the effect of application rate, growth stage, and tank mixing azimsulfuron, bentazon, MCPA, propanil, or cyhalofop on the efficacy of bispyribac–sodium against early watergrass and late watergrass from rice fields in northern Greece. Mixtures of bispyribac–sodium with the insecticides carbaryl, diazinon, and dichlorvos were also evaluated. Bispyribac–sodium (24 to 36 g ai/ha) applied alone at the three- to four-leaf growth stage provided 89 to 100% control of early watergrass and 84 to 100% control of late watergrass. When bispyribac–sodium was applied alone at the five- to six-leaf growth stage of early watergrass and late watergrass, control ranged from 78 to 100% and 71 to 100%, respectively. Mixtures of bispyribac–sodium with azimsulfuron provided better control of both species at any growth stage than bispyribac–sodium applied alone. On the contrary, mixtures of bispyribac–sodium with bentazon, MCPA, or propanil were less effective on both species at any growth stage than bispyribac–sodium applied alone. A slight efficacy reduction occurred on both species for the mixture of bispyribac–sodium with cyhalofop. Mixtures of bispyribac–sodium with the insecticides carbaryl or dichlorvos showed reduced efficacy on both species, whereas increased efficacy on both species was observed for mixtures of bispyribac–sodium with diazinon as compared with the single application of bispyribac–sodium.

Experiments were conducted in 2005 and 2006 near Huntley, Montana to evaluate two formulations of mesosulfuron-methyl for the control of wild oat in malt barley. The two formulations differed due to the amount of safener, mefenpyr-diethyl, that each contained. Formulation 1 and 2 contained mesosulfuron-methyl and mefenpyr-diethyl at a 1 : 2 and 1 : 6 ratio, respectively. The two formulations were applied alone at two rates or in combination with other small grain herbicides that are typically used for broadleaf weed control. The low and high rate of formulation 1 contained 7.8 and 10.1 g ai/ha of mesosulfuron-methyl and 15.6 and 20.2 g ai/ha of mefenpyr-diethyl, respectively. The low and high rate of formulation 2 contained 2.5 and 3.1 g ai/ha of mesosulfuron-methyl and 15 and 18.6 g ai/ha of mefenpyr-diethyl, respectively. These treatments were compared to a standard treatment of fenoxaprop and a nontreated control. In 2005, formulation 2 applied alone at the low and high rates caused barley injury of 7 ...

Experiments were conducted to study the effect of application rate, growth stage, and tank-mixing azimsulfuron or bentazon on the activity of cyhalofop, clefoxydim, and penoxsulam against two morphologically distinctEchinochloaspecies from rice fields in Greece. Mixtures of penoxsulam with MCPA were also evaluated. Cyhalofop (300 to 600 g ai/ha) applied at the three- to four-leaf growth stage provided 62 to 85% control of early watergrass but 41 to 83% control of late watergrass averaged over mixture treatments. Control ranged from 37 to 80% for early watergrass and from 35 to 78% for late watergrass when cyhalofop was applied at the five- to six-leaf growth stage averaged over mixture treatments. Mixtures of cyhalofop with azimsulfuron or bentazon reduced efficacy on both species irrespective of growth stage or cyhalofop application rate compared with cyhalofop alone. Clefoxydim (100 to 250 g ai/ha) applied alone at the three- to four-leaf growth stage provided 98 to 100% control of early watergrass and 91 to 100% control of late watergrass; when clefoxydim was applied alone at the five- to six-leaf growth stage the control obtained was 91 to 100% for early watergrass and 79 to 100% for late watergrass. Mixtures of clefoxydim with azimsulfuron or bentazon reduced efficacy on late watergrass at the early growth stage and on both species at the late growth stage. Penoxsulam (20 to 40 g ai/ha) applied alone provided 94 to 100% control of both species at both growth stages. Mixtures of MCPA with penoxsulam reduced efficacy on late watergrass at the early growth stage and on both species at the late growth stage. Mixtures of penoxsulam with azimsulfuron or bentazon reduced efficacy only on late watergrass at the late growth stage.

A host-specific fungusColletotrichum truncatumstrain 00-3B1 (Ct) was mixed with herbicides to improve the control of scentless chamomile, a noxious weed in western Canada. The compatibility of Ct conidia (spores) with herbicides was evaluated in vitro, and varying effects were observed with different products on spore germination. Clodinafop, glufosinate, MCPA, and 2,4-D ester were relatively benign and delayed the germination slightly, whereas dicamba, imazethapyr, metribuzin, and 2,4-D amine were noticeably more inhibitive. Bromoxynil, glyphosate, sethoxydim, and Merge®(spray adjuvant) were most inhibitive, showing >50% inhibition after 24 h. To determine potential synergy, Ct was applied at 7 × 106spores/ml in tank mixtures with selected herbicides at 1× and 0.1× registered rates under greenhouse conditions. Combining Ct with MCPA, 2,4-D ester, clopyralid, or metribuzin at 1× rate resulted in synergistic or additive interaction on scentless chamomile, increasing weed control significantly when compared to Ct or herbicides applied alone. Similar applications of Ct with imazethapyr, 2,4-D amine, dicamba, or glyphosate were antagonistic. Treatments with Ct plus 1× metribuzin killed scentless chamomile completely, whereas neither Ct nor the herbicide alone caused plant death, suggesting the value of this tank mixture.

Field experiments were conducted during 3 yr in Thessaloniki, northern Greece, to determine the efficacy of various herbicides applied alone or in mixtures POST on hoary cress grown in winter wheat. Also, the efficacy of these herbicides on hoary cress generated from seed or root fragments was investigated in pot experiments. All herbicides except for ioxynil plus bromoxynil provided 90 to 100% control of hoary cress generated from seed and root fragments grown in pots. Ioxynil plus bromoxynil gave 84% control of hoary cress generated from seed, but only 66% control of plants generated from root fragments. In the field, mecoprop plus dicamba, imazamethabenz plus mecoprop plus dicamba, and triclopyr applied at the four- to eight-leaf stage provided, respectively, 87, 76, and 83% control of hoary cress (averaged over year and assessment time). Thifensulfuron plus tribenuron provided only 29% control. Chlorsulfuron plus dicamba, clopyralid plus MCPA, 2,4-D plus metosulam, and fluroxypyr provided intermediate hoary cress control. Furthermore, the least hoary cress emergence 52 wk after treatment appeared in plots treated with triclopyr. In addition, wheat grown in plots treated with mecoprop plus dicamba yielded more than wheat treated with the other herbicide treatments, and 55% more than wheat grown in nontreated plots. The results of this study indicate that very good control of hoary cress and high wheat yield can be obtained by the application of mecoprop plus dicamba at the four- to eight-leaf weed growth stage.

Field studies were conducted at Shiraz, Iran, during 2000 and 2001 to investigate the effect of separate and combined herbicide treatments on weed control and corn yield. Separate and combined herbicide treatments included 14 combinations applied at two rates. Herbicides reduced weed biomass compared with the weedy check. In both years, maximum reduction in weed biomass was observed with atrazine plus alachlor at 1 + 2.44 and 1.5 + 1.92 kg ai/ha and minimum reduction in weed biomass was observed with rimsulfuron at 0.02 and 0.04 kg/ha. In 2000 and 2001, 2,4-D plus MCPA at 0.36 + 0.31 and 0.54 + 0.46 kg/ha, and alachlor plus 2,4-D plus MCPA at 1.92 + 0.54 + 0.46 kg/ha, and 2.44 + 0.36 + 0.31 kg/ha, controlled 80 to 100% of field bindweed and rimsulfuron at 0.02 and 0.04 kg/ha controlled 17 to 70% of field bindweed. All herbicide treatments controlled redroot pigweed 60 to 100%. In 2000, at 6 and 17 WAP, minimum biomass reduction of Chinese-lantern-plant was observed with 2,4-D plus MCPA at 0.36 + 0.31 and 0.54 + 0.46 kg/ha, and primisulfuron plus prosulfuron at 0.02 + 0.02 and 0.03 + 0.03 kg/ha. Rimsulfuron plus primisulfuron plus prosulfuron at 0.02 + 0.03 + 0.03 and 0.04 + 0.02 + 0.02 kg/ha reduced johnsongrass biomass 96 to 100% and the efficacy of rimsulfuron increased when tank mixed with primisulfuron plus prosulfuron. Results of both years showed that all herbicide treatments increased corn grain yield as compared with the weedy check. Maximum corn grain yield was obtained with combinations of atrazine plus alachlor at 1 + 2.44 and 1.5 + 1.92 kg/ha.

Phenoxy herbicides are frequently used to control volunteer canola populations. However, there have been claims that poor control could be due to cold acclimation of canola plants in the spring. The objective of this study was to determine whether cold acclimation or growth stage affected the response of canola volunteers to herbicides. In a growth room experiment, canola plants were prehardened and cold acclimated or were grown at 20/12 C and treated with one of six 2,4-D doses. Cold acclimation as achieved by this experiment affected upper and lower asymptotes of the dose–response curve but not the herbicide dose required to reduce canola weight by 50% relative to the nontreated control (GR50), indicating limited cold-related effects on canola tolerance to 2,4-D. Field experiments, conducted in the provinces of Québec and Saskatchewan, examined the effects of canola growth stage on the efficacy of 2,4-D, MCPA, and carfentrazone. Comparisons of the estimates from the dose–response curves confirmed that herbicide efficacy was consistently greater when canola plants were treated at an early growth stage, regardless of cultivar or herbicide used. The GR50estimates for canola plants treated at a later growth stage exceeded the recommended rates. Some canola plants grown as volunteers in a wheat crop survived 2,4-D or MCPA treatments at 0.5× and 1× rates and produced up to 148 seeds/m2. Efficient control of canola volunteers will be obtained when plants are sprayed at an early growth stage, but near-total control will be highly desirable in order to restrict seedbank buildup, particularly when dealing with canola cultivars with different herbicide-resistant traits.

There is a high potential for inadvertent herbicide injury to crops in western Canada on an annual basis because of the diversity of crops grown in close proximity to each other, although accurate data regarding the annual number of injury incidents is not available. A field study was conducted at two locations in southern Manitoba, Canada, in 2001 and 2002, to investigate the effects of a range of dosages of MCPA ester, glyphosate, and thifensulfuron:tribenuron (2:1) applied to the seedling growth stage of conventional (nongenetically engineered) canola and white bean on subsequent shoot dry matter and crop yield. Similar to other studies that utilized sublethal herbicide dosages, results between site-years were variable, particularly for crop yield. Where possible, a nonlinear log-logistic model was fitted to the data. Generally, canola was more sensitive than white bean to the herbicides used in this study. Based on the fitted regression equations and recorded mean values for canola, 10% of the commercial herbicide dosage normally applied in other (possibly adjacent) crops caused greater than 10% canola yield loss for 9 of 12 unique combinations of herbicide-site-year. For white bean, 10% of the commercial herbicide dosage caused yield losses greater than 10% for only 4 of 13 unique combinations of herbicide-site-year. Spray drift is probably the most common source of inadvertent application of herbicide to sensitive crops; generally, only a fraction of the herbicide dosage applied on an adjacent crop drifts off-target. The results of this study indicate that for any of the three herbicides investigated on canola and white bean, it is difficult to accurately predict eventual crop yield loss based on early season sublethal herbicide injury symptoms due to site-year variability and the potential for crop recovery and compensatory growth. This response was particularly true for white bean in this study.

Field experiments were conducted at three locations in 2003 and 2004 to examine clethodim and quizalofop-P efficacy on spring wheat seedlings when applied alone or in tank mixtures with herbicides used to control broadleaf weeds. Clethodim at the recommended rate of 30 g/ha reduced spring wheat biomass by 63 to 98% and was only >90% in three of six site years. In contrast, quizalofop-P at the recommended rate of 36 g/ha reduced wheat biomass >90% in all cases. Clethodim or quizalofop-P could be tank mixed with 2,4-D ester, bromoxynil, or bromoxynil plus MCPA ester with little risk of reduced efficacy on wheat. However, 2,4-D amine was highly antagonistic to both herbicides. The commercial mixture of thifensulfuron plus tribenuron reduced clethodim, but not quizalofop-P, efficacy on wheat. Herbicide options exist for simultaneous control of volunteer glyphosate-resistant canola and glyphosate-resistant wheat if the latter technology were to be commercialized in the future. Nomenclature: Bromoxynil; clethod...

The agrestal field violet, a pervasive weed in Europe, has been identified in reduced-tillage cereal fields in Alberta. The efficacy of herbicides in direct-seeded spring wheat was assessed on natural field violet infestations in Alberta in 2002 and 2003. Only fluroxypyr + 2,4-D, applied postemergence, provided control of field violet in 2002 when rainfall was limiting. Over both years, this herbicide combination reduced biomass by 59 to 69% and plant density by 83 to 91%, relative to nontreated plots. The herbicides metsulfuron, sulfosulfuron, and thifensulfuron + tribenuron only suppressed weed growth under drought conditions in 2002 but controlled the weed in 2003 when rainfall was greater, reducing plant density by 82 to 92% and rendering remaining plants sterile. Suppression was also observed with MCPA + mecoprop + dicamba in 2002 and 2003 and with metribuzin only in 2003. Effective control of field violet was conferred by a pre–crop emergence application of glyphosate at 445 g ae/ha in 2003, the only year that this treatment was evaluated. Activity of herbicides on three- to four-leaf seedlings was also evaluated in a greenhouse dose– response assay. All herbicides had greater efficacy in the greenhouse, and those that provided control in situ reduced field violet dry weight by 85% at less than the recommended rate used in field experiments. Management of field violet is possible with herbicides registered for use on spring wheat in Alberta. However, the weed does not appear to cause significant crop production losses; hence, herbicide selection should be based on knowledge of all weed species present within the field.

Glyphosate-resistant canola was seeded at Vegreville, Alberta, in 1997 and 1999 and barley in rotation with the canola in 1998 at three seeding rates. The effects, at each crop seeding rate, of variable glyphosate (canola) and tralkoxydim plus bromoxynil plus MCPA (barley) rates on crop yield, net economic return and seed production by wild oat, wild mustard, and wild buckwheat, and the amount of weed seed in the soil seed bank was determined. Crop seeding rate influenced the response of canola and barley yield and weed seed production to herbicide rate. At the lowest crop seeding rates, yield responses tended to be parabolic with yields increasing up to one-half and three-quarters of the recommended herbicide rates and trends toward reduced yields at the full rates. This response was not evident at the higher crop seeding rates, where, in most cases the yield reached a maximum between one-half and the full recommended rate. The effects of the herbicides on weed seed production, especially at the lowest rate, were often superior at the higher crop seeding rates. The results indicate that seeding canola and barley at relatively high rates may reduce risk associated with lower crop yields and increased weed seed production at lower than recommended herbicide rates. However, the current cost of herbicide-resistant canola seed may preclude the adoption of this integrated weed management practice by growers.

Auxin-type herbicides such as 2,4-D and dicamba are commonly used to control kochia in small grain production areas, but poor kochia control with these herbicides has been reported. Several auxinic herbicide-resistant kochia inbreds were evaluated for their response to 2,4-D or dicamba and to alternative herbicide treatments. Values of the dose of the herbicide causing 50% visible injury to test plants (I50) from week 1 to week 4 after treatment with 2,4-D were unchanged for six of the seven 2,4-D–resistant inbreds, indicating that these plants may recover to produce seeds. In contrast, the corresponding I50 values for dicamba decreased for five of the six dicamba-resistant inbreds, indicating that kochia was not recovering from the treatment. Postemergence treatments with atrazine, carfentrazone, fluroxypyr, bromoxynil plus MCPA, nicosulfuron plus dicamba, and nicosulfuron plus dicamba plus atrazine, all provided adequate to excellent control of resistant kochia inbreds. Alternative chemical control opti...

Lawn burweed is a serious problem in warm-season golf courses, sports fields, and residential turfgrass. Field studies were conducted at three sites in Florida to evaluate herbicides applied postemergence for control of lawn burweed. Mecoprop + 2,4-D + dicamba provided > 95% control of lawn burweed when evaluated 47 to 55 d after treatment (DAT). MCPA + triclopyr + dicamba in either ester or amine forms, 2,4-D + triclopyr + dicamba, triclopyr, 2,4-D, and bromoxynil provided 88 to 100% control 40 to 55 DAT. Although triclopyr + clopyralid provided > 90% control in one study, it was not consistent and controlled

MKH 6562 is a new acetolactate synthase inhibitor herbicide that would provide an alternative to control wild oat. Three experiments were conducted at Scott, SK, Canada, from 1996 to 1999 to evaluate MKH 6562 rates (20 and 30 g ai/ha), carrier volumes (30, 50, and 100 L/ha), time of applications (two- to three-leaf and three- to four-leaf stages of wild oat), and broadleaf weed herbicide tank mixtures. Reduced wild oat control (lower visual rating of percent control and higher fresh weight) often occurred when MKH 6562 was applied at a rate of 20 vs. 30 g/ha, with carrier volumes of 30 vs. 50 and 100 L/ha, and at the three- to four-leaf vs. two- to three-leaf stages of wild oat. Wild oat control generally was lower for MKH 6562 tank mixed with dicamba + mecoprop + MCPA 1:1:4.4 and bromoxynil + MCPA 1:1 compared with MKH 6562 applied alone or tank mixed with other broadleaf herbicides. MKH 6562 tank mixed with MCPA, and to a lesser extent 2,4-D, resulted in decreased wild oat control when applied...

Kochia (Kochia scoparia) control dropped from about 90% to less than 20% after three consecutive annual applications of acetolactate synthase (ALS)-inhibiting herbicides in several northeastern South Dakota fields. Field experiments were conducted to evaluate control of kochia resistant to ALS-inhibiting herbicides using combinations of herbicides applied postemergence (POST) in wheat (Triticum aestivum) and using herbicides applied preemergence (PRE), POST, and PRE plus POST in soybean (Glycine max). Thifensulfuron plus tribenuron did not control kochia in wheat (> 600 kochia plants/m2 at harvest) and wheat yield was similar to yield of the untreated control. Dicamba plus 2,4-D (in 1996) and bromoxynil plus MCPA (in 1996 and 1997) controlled kochia and increased yields by 15% or more. Kochia was sparse (less than 1 plant/m2) in soybean plots, but grass weeds were prevalent. PRE plus POST or POST herbicide combinations that included ALS-inhibiting herbicides controlled grasses, and soybean yield...

Combinations of 0 to 1,120 g ae/ha 2,4-D plus 0 to 42 g ai/ha metsulfuron were evaluated in both field and greenhouse experiments. Addition of metsulfuron to 2,4-D increased Virginia buttonweed (Diodia virginiana) fresh weight reduction in the greenhouse compared with 2,4-D alone, but reduction in fresh weight was not different from 32 g/ha or more of metsulfuron applied alone. In field experiments 5 wk after treatment (WAT), combinations of metsulfuron and 2,4-D did not control Virginia buttonweed greater than 32 g/ha or more of metsulfuron alone. No synergism for the combinations was observed. Field experiments conducted from 1991 to 1993 evaluated three-way combinations of herbicides for Virginia buttonweed control. Treatments included: 2,4-D plus mecoprop plus dicamba (five herbicide premixes), 2,4-D plus dichlorprop plus dicamba, 2,4-D plus MCPA plus dichlorprop, mecoprop plus MCPA plus dichlorprop, or 2,4-D plus mecoprop plus dichlorprop. Combinations containing at least 688 g/ha 2,4-D pro...

Field studies evaluated wild radish control in oat with thifensulfuron plus tribenuron in 1995 and 1997. Thifensulfuron plus tribenuron at 16 or 21 g ai/ha controlled wild radish completely in both years. In tolerance studies conducted in 1995 and 1996, thifensulfuron plus tribenuron reduced vigor of Bay', 'Belle,' 'Dane,' Ensiler,' 'Gem,' 'Horicon,' Ogle,' 'Porter,' and Prairie' oat varieties and Wisconsin test selection oat X6396-1' up to 25% 7 d after treatment (DAT), but all chlorotic symptoms had disappeared 28 DAT. Thifensulfuron plus tribenuron reduced oat height 13 to 19% in 1995 and 21 to 24% in 1996 7 DAT. Bay, Belle, Dane, Ensiler, Horicon, Prairie, and X6396-1 recovered from height reductions by 28 DAT in 1995; however, in 1996 only Horicon and Porter recovered. Thifensulfuron plus tribenuron did not reduce 1995 grain yields, but 1996 Bay and Porter grain yields were reduced 29 and 15%, respectively. Dane and Prairie seed weights were reduced 7 and 14%, respectively, in 1995, whereas no seed weight reduction occurred in 1996. Nomenclature: Thifensulfuron, 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino] sulfonyl]-2-thiophenecarboxylic acid; tribenuron, 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)methylamino]carbonyl]amino]sulfonyl]benzoicacid; wild radish, Raphanus raphanistrum L. # 3 RAPRA: oat, Avena sativa L., Bay, Belle, Dane, Ensiler, Gem, Horicon, Ogle, Porter, Prairie, X6396-1.

Spring barley often is grown in rotation with winter wheat, and sometimes barley can overwinter in the subsequent winter wheat crop reducing grain yield and quality. Studies were es- tablished during 1996 and 1997 in winter wheat fields in southeastern Washington and near Moscow, ID, respectively, to evaluate control of 'Steptoe' volunteer barley with MON 37500, diclofop, and fenoxaprop/2,4-D/MCPA. Herbicides were applied to volunteer barley at two growth stages: two leaves to four tillers and more than four tillers with stems beginning to elongate. MON 37500 at 0.018, 0.026, and 0.035 kg ai/ha visibly controlled volunteer barley 83% or more at both application times. Diclofop at 1.12 kg ai/ha did not control volunteer barley, whereas fenoxaprop/2,4-D/MCPA at 0.66 kg ai/ha controlled volunteer barley 64 to 97% in 1996, but only 0 to 23% in 1997. In 1996 and 1997, volunteer barley density was reduced 80 to 99% in MON 37500-treated plots compared to the untreated control plots. Wheat grain grade was #1 for all MON 37500 treatments compared to grade #4 in 1996 and #3 in 1997 in the untreated plots. Grain price was reduced by dockage (barley kernels) for MON 37500-treated wheat $0 to $3.12/metric ton (MT), whereas price was reduced $23 to $26/MT for grain from untreated plots. In greenhouse studies, visible injury and height and biomass reduction varied among the 36 barley varieties treated with MON 37500. Nomenclature: Diclofop-methyl, methyl 2-(4-(2,4-dichlorophenoxy)phenoxy)propanoate; fenoxaprop/ 2,4-D/MCPA, fenoxaprop-p-ethyl, (+ )-ethyl 2-(4-((6-chloro-2-benzoxazoly)oxy)phenoxy)propanoate; 2,4-D isooctylester, 2-ethylhexyl-(2,4-dichlorophenoxy)acetate; MCPA isooctylester, isooctyl(4-chloro-2- methyl-phenoxy)acetate; MON 37500, 1-(2-ethylsulfonylimidazo(1,2-a)pyridin-3-ylsulfonyl)-3-(4,6-di- methoxypyrimidin-2-yl)urea; volunteer barley, Hordeum vulgare L. 'Steptoe'; winter wheat, Triticum

Green and yellow foxtail seed production following harvest of spring wheat is a concern of producers in the northern Great Plains of the United States and the Prairie Provinces of Canada. Experiments were conducted in 1996 and 1997 in three tillage systems, no till (NT), chisel plow (CP), and moldboard plow (MP), at the University of Minnesota West Central Experiment Station, Morris, MN, to determine whether time of glyphosate application or tillage after spring wheat harvest could reduce postharvest foxtail seed production. In both years, hard red spring wheat was planted in late April and a packaged mixture of fenoxaprop and 2,4-D ester and MCPA ester was applied at a rate of 53 g and 81 g and 246 g ai/ha for grass and broadleaf weed control. Following spring wheat harvest, each main plot was subdivided into seven subplots, including an untreated control. One subplot was disked twice at 4 to 6 d after harvest (DAH) of spring wheat, and five other subplots had glyphosate (0.25 kg ai/ ha) applied on different days (1 to 31 DAH). Foxtail seeds were collected from the soil surface following first frost, and the number of green and yellow foxtail seeds were determined. Tillage immediately after spring wheat harvest eliminated foxtail plants, and no new foxtail seedlings emerged in either tilled or glyphosate-treated plots despite ideal postharvest conditions for foxtail germination and emergence in 1997. Most viable green foxtail seeds were consistently obtained in NT plots, whereas yellow foxtail seed production varied among tillage systems. Either tillage soon after spring wheat harvest or glyphosate application within 16 DAH reduced green and yellow foxtail seed production by greater than 70%. Nomenclature: Fenoxaprop, (±)-2-[4-[(6-chloro-2- benzoxazolyl)oxy]phenoxy]propanoic acid; glyphosate, N- (phosphonomethyl)glycine; MCPA, (4-chloro-2-methylphenoxy)acetic acid; 2,4-D, (2,4-dichlorophenoxy)acetic acid; green foxtail, Setaria viridis (L.) Beauv. # 3 SETVI; yellow foxtail, Setaria glauca (L.) Beauv. # SETLU; wheat, Triticum aestivum L. 'Sharpe'.

The affect of mesosulfuron and tribenuron applied POST to oat and rye was determined at three locations in Georgia during 2004 and 2005. Five herbicide treatments were applied to oat and rye in Feekes scale (FS) 1.2 or 2 developmental stage. Herbicide treatments consisted of tribenuron at 13 or 26 g ai/ha, tribenuron at 13 g/ha plus MCPA at 561 g ai/ha, MCPA at 561 g/ha, and mesosulfuron at 15 g ai/ha. Tribenuron, MCPA, and tribenuron plus MCPA injured both crops less than 4% and did not affect grain yield. Mesosulfuron applied to rye in FS 1.2 injured the crop 36% at 2 wk after treatment (WAT), 12% at 5 WAT, and 0% at harvest. Mesosulfuron applied at FS 2 injured rye less than 9%. Mesosulfuron did not influence rye-grain yield with either application timing. Mesosulfuron injured oat 65 to 86% at 5 WAT and reduced yield at least 70% regardless of application timing. Nomenclature: MCPA; mesosulfuron-methyl; tribenuron-methyl; oat, Avena sativa L. ‘Horizon 32’; rye, Secale cereale L. ‘Wrens 96’.

Rates and application timings of postemergence herbicides for wild oat control in spring wheat and barley were evaluated at Crookston, MN, from 1994 to 1996. Diclofop, imazamethabenz, and fenoxaprop plus MCPA plus thifensulfuron plus tribenuron were applied to one- to three-leaf wild oat; and difenzoquat, imazamethabenz, fenoxaprop plus MCPA plus thifensulfuron plus tribenuron, and fenoxaprop plus 2,4-D plus MCPA were applied to four- to five-leaf wild oat at 1/2 ×, 3/4 ×, and 1 × rates. Wild oat response to herbicide rate and timing was similar in wheat and barley. Wild oat control with 1/2 × rates generally was less than that with 3/4 × rates, which was lower than or similar to that with 1 × rates. Wild oat biomass was often reduced less with 1/2 × rates than 1 × rates. However, reducing herbicide rates generally did not influence grain yields or net economic return. Grain yields and net economic return were generally greater in herbicide-treated plots than in the nontreated control.

Studies were conducted at Rosemount and Crookston, MN, in 1994 and 1995 to determine weed control efficacy and crop injury of F8426 (proposed common name carfentrazone-ethyl) in hard red spring wheat. F8426 alone and with 2,4-D or dicamba generally controlled common lambs- quarters, kochia, and velvetleaf 90% or more at 0.026 and 0.035 kg/ha. F8426 alone and with 2,4-D or dicamba controlled Pennsylvania smartweed, wild buckwheat, and wild mustard 39 to 100% and was less consistent than control of the aforementioned species. Weed control varied little among the F8426 rates. Weed control was inconsistent between location, year, and species when F8426 was combined with crop oil concentrate, urea-ammonium nitrate solution, and nonionic surfactant. Con- trol was more consistent when 0.28 kg/ha 2,4-D or 0.07 kg/ha dicamba was tank mixed with either F8426 rate. The best control with an F8426 treatment was similar to control from MCPA tank mixed with thifensulfuron plus tribenuron, bromoxynil, or dicamba. Weed control 30 and 45 days after treatment (DAT) was less for F8426-containing treatments than standard treatments, which likely was related to reduced crop competition after severe crop injury. Increasing F8426 rate from 0.026 to 0.035 kg/ha did not greatly increase wheat injury, whereas adding 0.28 kg/ha 2,4-D to either F8426 rate greatly increased crop injury. Wheat yield was reduced up to 63% by F8426 and 2,4-D combinations. Nomenclature: Bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; dicamba, 3,6-dichloro-2-methoxy- benzoic acid; F8426 (proposed common name, carfentrazone-ethyl), ethyl, 2-dichloro-5-(4-(difluo- romethyl)-4,5-dihydro-3-methyl-5-oxo- 1H- 1,2,4-triazol- 1-yl)-4-fluorobenzenepropanoate; MCPA, (4-chloro-2-methylphenoxy)acetic acid; thifensulfuron, 3-(((((4-methoxy-6-methyl-1,3,5-triazin-2- yl)amino)carbonyl)amino)sulfonyl)-2-thiophenecarboxylic acid; tribenuron, 2-(((((4-methoxy-6-meth- yl-1,3,5-triazin-2-yl)methylamino)carbonyl)amino)sulfonyl)benzoic acid; 2,4-D, (2,4-dichloro- phenoxy)acetic acid; common lambsquarters, Chenopodium album L., #3 CHEAL; kochia, Kochia scoparia (L.) Schrad. # KCHSC; Pennsylvania smartweed, Polygonum pensylvanicum L. # POLPY; velvetleaf, Abutilon theophrasti Medik. # ABUTH; wild buckwheat, Polygonum convolvulus L. # POLCO; wild mustard, Brassica kaber (DC.) L. C. Wheeler # SINAR; hard red spring wheat, Trit- icum aestivum L. 'Marshall' and '2375.' Abbreviations: ALS, acetolactate synthase; DAT, days after herbicide treatment; COC, crop oil

Trifluralin is used for weed control in wheat but may reduce vegetative growth and yield. Postemergence (POST) herbicides may cause additional plant stress to trifluralin-stressed wheat. Field studies at Groton, SD in 1991 and 1992 and at Highmore, SD in 1992 evaluated the effects of 2,4-D-amine, difenzoquat, metsulfuron, and a combination of fenoxaprop-ethyl + 2,4-D-ester + MCPA-ester on hard red spring wheat cultivars '2375,' 'Prospect,' and 'Butte 86' seeded in areas treated with preplant incorporated trifluralin either in the spring before seeding (0.56 kg ai/ha) or the previous year (1.12 or 2.24 kg ai/ha). Trifluralin applied alone in the spring, and followed by some POST herbicides, reduced shoot dry weight and grain yield. Trifluralin reduced the yield of Prospect the most and the yield of 2375 the least. Yields of trifluralin-treated wheat were reduced 23% by metsulfuron and 14% by fenoxaprop-ethyl + 2,4-D + MCPA compared to yields of wheat treated with only the respective POST herbicide. Yields were not reduced with any trifluralin-POST herbicide combination when trifluralin was applied a year prior to seeding wheat. Nomenclature: Difenzoquat, 1,2-dimethyl-3,5-diphenyl-1H-pyrazolium; fenoxaprop-ethyl, (±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid; MCPA, (4-chloro-2-methylphenoxy)acetic acid; metsulfuron, 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid; trifluralin, 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine; 2,4-D, (2,4-dichlorophenoxy)acetic acid; wheat, Triticum aestivum L.

Thirteen field experiments were conducted to evaluate quinclorac for cheat control in hard red winter wheat. Cheat control with quinclorac was variable. Quinclorac at 560 and 1120 g a.i./ha applied to tillered wheat controlled cheat 93 to 100% at four sites. In contrast, pooled over four other experiments and four application times, quinclorac at 420 g/ha and 560 g/ha controlled cheat only 20 and 31%, respectively. Quinclorac at 420 g/ha plus chlorsulfuron:metsulfuron (5:1) at 35 g a.i./ha applied PRE increased wheat yield 28% at one of three sites. At two of these sites, averaged over chlorsulfuron:metsulfuron rates of 0, 18, and 35 g a.i./ha, quinclorac at 280 and 420 g/ha applied POST, increased wheat yield 32 to 112%. In two cultivar tolerance experiments, quinclorac treatments did not damage any cultivar. Pooled over cultivars, yields were increased 7 and 10% when quinclorac at 280 and 560 kg/ha was applied, respectively. In a greenhouse experiment, quinclorac plus dicamba or esfenvalerate consistently reduced the leaf area of cheat in a manner suggesting synergistic effects. Of eight adjuvants evaluated in a laboratory experiment, only quinclorac plus the adjuvant BCH 864 01S reduced cheat leaf area more than quinclorac alone.

Seventeen on-farm and two experiment station experiments were conducted to evaluate farmers' decisions to apply broadleaf weed control herbicides to tillered hard red winter wheat in February or March with or without urea-ammonium nitrate (28-0-0) fertilizer carrier. The herbicides and rates varied by farm, but all farmers applied a residual sulfonylurea herbicide and four added a phenoxy herbicide. Most farmer-selected herbicide treatments controlled target weeds including bushy wallflower, flixweed, henbit, plains coreopsis, smallflowered bittercress, and wild buckwheat. Controlling these weeds increased wheat yield on only two farms. Farmer-selected, commercially applied treatments increased net returns at two of seventeen farms, decreased net returns at seven farms, and did not affect returns at eight farms. Net returns were increased over the farmer-selected treatments at two farms when half the farmer-selected rate of herbicide was used. Half-rate herbicide treatments controlled weeds up to 25% less than farmer-selected treatments. Weed control with the half-rate treatments ranged from 60 to 98%. None of the farmers expected that herbicide use would increase yield. Their primary objective was to have weed-free fields at harvest. Nitrogen rates appeared to be selected without a rational basis for decision making.

Field studies were undertaken in 1992 and 1993 to investigate the control of wild oat and green foxtail in flax with reduced rates of fluazifop-P and clethodim applied as tank-mixtures. Fluazifop-P plus clethodim at 50 + 18 g ai/ha controlled wild oat and green foxtail and was as effective as full rates of either herbicide applied alone. These rates represent a 20% reduction in total amount of active ingredient required to control wild oat and green foxtail. Application of fluazifop-P, and/or clethodim prior to the 3- to 4-leaf stage failed to control late emerging grass weeds. Application of graminicide mixtures at or after the 3- to 4-leaf stage controlled late emerging grass weeds and did not affect flax yield. When applied late, fluazifop-P at 175 g/ha tended to reduce flax yield, although weed control was acceptable and no foliar injury was observed following treatment. The efficacy of graminicide mixtures was reduced by addition of bromoxynil plus MCPA to the spray mix.

In a two-year study involving two sites in western Canada, the dissipation of bromoxynil octanoate alone at 0.35 or 0.42 kg phenol equivalent (pe)/ha and the tank mixture of MCPAiso-octyl ester at 0.28 kg ae/ha plus bromoxynil octanoate at 0.28 kg pe/ha was monitored in postemergence-treated triticale. Initial foliar residues on the day after application (three- to four-leaf stage of the crop) were of the order of 14 and 5 mg/kg for MCPA and bromoxynil, respectively. Residues of both herbicides decreased to less than the limit of quantification (0.025 mg/kg) of the analytical method 21 d after application. At crop maturity, herbicide residues were non-detectable in the straw and seed. There was little or no effect on the dissipation of bromoxynil residues due to tank mixing with MCPA.

The effectiveness of single and repeated annual preharvest glyphosate applications (1 to 2 wk before crop harvest) to reduce Canada thistle populations was evaluated in field experiments near Bezanson, AB, Scott, SK, and St. Albert, AB. Single applications of glyphosate at 0.45 to 1.8 kg/ha at Bezanson and St. Albert reduced Canada thistle shoot density by more than 75% but in the three experiments at Scott 1.8 kg/ha was required to consistently obtain a similar reduction. Four consecutive, annual applications of glyphosate at 0.45 kg/ha or more did not eliminate Canada thistle but reduced shoot densities by more than 98% at Bezanson. At Scott, similar reductions occurred in two of three sites following two consecutive, annual preharvest applications of glyphosate at the same rates. In the third Scott site the 1.8 kg/ha rate of glyphosate provided a similar reduction but lower rates did not. At Bezanson, barley yields following the first, second, and third applications of glyphosate at 0.45 kg/ha or more were 14% greater than check plots where MCPA was applied in the spring. Yields of wheat seeded 1 yr after a single application of glyphosate at St. Albert were 26% greater than from unsprayed checks. Barley yields seeded 1 yr after each glyphosate application at Scott were not affected because Canada thistle populations were sparse.

A range of herbicide treatments was evaluated for long-term control of rush skeletonweed, a perennial weed of crops and pastures in North and South America, the Mediterranean region, central Europe, and Australia. Clopyralid (75 to 300 g ai/ha) and clopyralid mixtures with 2,4-D, MCPA, or dicamba were effective, resulting in survival rates of 0 to 4% for the most successful treatments applied for three consecutive seasons. Metsulfuron (9 g ai/ha) and 2,4-D (850 g ai/ha) significantly reduced survival when applied at high rates for three years. Barley yield in the season following control was increased by up to 195 to 199% of yield from untreated plots. Evidence was found for differences in herbicide susceptibility between narrowleaf and broadleaf forms of rush skeletonweed. Nomenclature: Clopyralid, 3,6-dichloro-2-pyridinecarboxylic acid; dicamba, 3,6-dichloro-2-methoxybenzoic acid; MCPA, (4-chloro-2-methylphenoxy)acetic acid; metsulfuron, 2-[[[[(4-methoxy-6-methyl1 ,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid; 2,4-D, (2,4-dichlorophenoxy)acetic acid; rush skeletonweed, Chondrilla juncea L. #3 CHOJU; barley, Hordeum vulgare L. Additional index words: Perennial weed, long-term control, yield increase, picloram. CHOJU.

Several sequences of POST herbicides applied each year in fall alone, in spring alone, or both in fall and again in spring controlled Canada thistle stands in spring wheat by severely decreasing root biomass and the numbers of adventitious root buds to a depth of 50 cm over four years. These treatments included dicamba applied at 1.7 or 2.2 kg ae ha–1for the first two successive falls followed in wheat by either chlorsulfuron at 30 g ai ha–1plus nonionic surfactant, MCPA plus bromoxynil at 280 plus 280 g ha–1, or 2,4-D amine at 560 g ha–1applied annually for each of four consecutive years from the start. Chlorsulfuron at 30 g ha–1applied alone in spring for each of four years also reduced and prevented Canada thistle root growth as effectively as a sequence of fall-applied dicamba followed by spring-applied chlorsulfuron in spring wheat.

The control of wild oat, volunteer wheat, and volunteer barley in a flax crop with sethoxydim was enhanced 20 to 27% by orienting the spray nozzles forward 45?. Control of annual grasses was not influenced by the time of day sethoxydim was applied. However, injury to flax from a tank mixture of sethoxydim and bromoxynilMCPA (1:1) was greatest when applied between 0500 and 1100 h, and least when applied between 1500 and 2300 h. Flax injury and reduced seed yields also resulted when sethoxydim was applied when air temperatures exceeded 30 C regardless of stage of crop growth. Nomenclature: Bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; MCPA, (4-chloro-2-methylphenoxy)acetic acid; sethoxydim, 2-[l-ethoxyimino)buty1]-5-[2ethylthio)propyl]-3-hydroxy-2-cyclohexen-l-one; wild oat, Avena fatua L. #3 AVEFA; barley, Hordeum vulgare L. # HORVX; flax, Linum usitatissimum L. 'Linott'; wheat, Triticum aestivum L. 'Katepwa'. Additional index words: Avena fatua, Hordeum vulgare, Triticum aestivum, AVEFA, HORVX

Commercial formulations of 33 herbicides, 12 fungicides, and 16 adjuvants were evaluated for their toxic effects on germination ofColletotrichum gloeosporioidesf. sp.malvae(C.g.m.) spores. At the recommended rates, none of the herbicides for grass weed control (diclofop, difenzoquat, fenoxaprop-ethyl, flamprop-methyl, and sethoxydim) or formulated herbicides registered for both broadleaf and grass weed control [diclofop plus bromoxynil (23:8), propanil, and propanil plus MCPA (7:2)] were compatible with C.g.m. spores. C.g.m. spore germination and appressorial formation recorded 24 h after exposure were totally inhibited by these herbicides. At recommended rates, herbicides for broadleaf weed control (2,4-D ester, 2,4-D amine, benazolin, bentazon, clopyralid, cyanazine, cyanazine plus MCPA (1:2), dicamba, dicamba plus MCPA (1:4), dicamba plus mecoprop plus MCPA (1:1:4.4), dicamba plus 2,4-D plus mecoprop (4.2:11:3), MCPA amine, MCPA-K, MCPA-Na, and metribuzin), caused no more than a 20% reduction in C.g.m. spore germination, and appressorial formation was not significantly reduced except by benazolin and metribuzin. Cyanazine and dicamba at recommended rates increased appressorial formation without reducing germination compared to the control. At lower concentrations, the other herbicides recommended for broadleaf weed control (2,4-DB, bromoxynil, bromoxynil plus MCPA (1:1), dichlorprop plus 2,4-D (1:1), imazethapyr, linuron, and picloram) were less toxic to C.g.m. spores. The fungicide triadimefon at recommended rate had no effect on C.g.m. spores. Dicloran reduced germination more than 50% at recommended rate and growth was distorted. At recommended rates, spore germination was inhibited by more than 90% with benomyl, carbathiin, chlorothalonil, iprodione, mancozeb, and thiophanate-methyl although germination increased as concentration declined. Spore germination was totally inhibited at all concentrations with ferbam, thiram, and captan. Exposure to the adjuvants—Agral 90, Alkasurf-0P-10, Atplus-555, Citowett Plus, Enhance, Renex 36, Triton XR, and X-77–inhibited C.g.m. spore germination and reduced spore production compared to the control. Spore germination was significantly higher in suspensions containing ammonium sulfate, Assist, Bio-veg, CD-407, and Tween 20, as well as with starch, sucrose, and water (control) than with the other adjuvants. Spore production was higher in suspensions containing starch and Bio-veg than in those with water and the other adjuvants.

Colletotrichum gloeosporioidesf. sp.malvae(C.g.m.) was evaluated under greenhouse conditions for round-leaved mallow control in combination with the following herbicides: bromoxynil plus MCPA (1:1), diclofop, imazethapyr, metribuzin, sethoxydim, and 2,4-DB. Treatments consisted of C.g.m. and herbicide applied alone, tank mixed, and C.g.m. applied 48 h before, and 1, 24, and 72 h after herbicide. Split applications with bromoxynil plus MCPA, imazethapyr, metribuzin, (C.g.m. before or after) and sethoxydim (C.g.m. before) enhanced round-leaved mallow control over C.g.m. applied alone. However, diclofop or 2,4-DB tank mixed or applied in a split application with C.g.m. did not improve round-leaved mallow control over C.g.m. applied alone. Bromoxynil plus MCPA, metribuzin, 2,4-DB, and imazethapyr may be tank mixed with C.g.m. without significantly reducing round-leaved mallow control, unlike sethoxydim or diclofop which inhibited C.g.m. development. Dew period did not influence the effectiveness of bromoxynil plus MCPA applied 30 h before C.g.m., but round-leaved mallow control increased with increasing dew period for metribuzin applied 30 h before C.g.m.

The effects of 14 herbicide treatments, tested in the establishment phase, were investigated on timothy productivity in two field experiments conducted at Melfort, Saskatchewan. Satisfactory weed control achieved with chlorsulfuron, metsulfuron, thifensulfuron, bentazon, diclofop plus bromoxynil, and MCPA/mecoprop/dicamba during the establishment year ensured good forage establishment which in turn caused a ‘residual effect’ for 1 to 3 yr increasing individual cut as well as cumulative forage dry matter yields significantly. In the stand established in 1985, when field pennycress (97 m-2) was the dominant weed in the seedling stage, these treatments increased yields 29 to 52% over a 3-yr period. In the stand established in 1986, when common lambsquarters (27 m-2) was the dominant weed, these treatments increased cumulative yields 24 to 44%. Sethoxydim and fenoxaprop, tested alone, caused significant crop injury in both experiments.