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Saflufenacil is a PRE herbicide for the control of broadleaf weeds. Field and growth room studies were conducted to explore the tolerance of corn to POST treatments of saflufenacil and BAS 781. Additionally, the potential use of sodium as a safener for saflufenacil was evaluated. Crop injury caused by saflufenacil or BAS 781 was 8 and 38%, respectively, when applied at twice the recommended dose at the spike to two-leaf stage of crop growth. This injury increased to 28 and 65%, respectively, when applied at the three- to four-leaf stage. This level of crop injury resulted in yield loss, particularly when applied at the three- to four-leaf stage. The addition of Na-bentazon to saflufenacil reduced this injury and increased crop dry weight under both field and laboratory conditions. In the field, Na-bentazon also increased corn collar height and yield compared with saflufenacil applied alone. Na-bentazon reduced injury through a reduction in foliar uptake of saflufenacil. Sodium derived from baking soda also provided a safening effect, but only at the lowest dose of saflufenacil tested.

There are a limited number of herbicide options available for durum wheat production in Ontario, Canada. Four field studies were conducted in Ontario, Canada over a three year period (2008, 2009 and 2010) to evaluate the sensitivity of spring planted durum wheat to post-emergence (POST) applications of dichlorprop/2,4-D, dicamba/ MCPA/mecoprop, clopyralid, bromoxynil/MCPA, pyrasulfotole/bromoxynil, thifensulfuron/tribenuron + MCPA amine, fluroxypyr + MCPA ester, tralkoxydim and fenoxaprop-p-ethyl/safener at the manufacturers’ recommended dose and twice that dose. Visible injury in durum wheat were 0 to 2.4% with dichlorprop/2,4-D, 0 to 6% with dicamba/MCPA/mecoprop, 0 to 0.4% injury with clopyralid, 0 to 1.4% injury with bromoxynil/MCPA, 0 to 3.5% with pyrasulfotole/bromoxynil, 0 to 5% with thifensulfuron/tribenuron + MCPA amine, 0 to 2.6% with fluroxypyr + MCPA ester, 0 to 5% with tralkoxydim and 0.4% to 8% with fenoxaprop-pethyl/safener at various evaluation dates (1, 2, 3 and 4 weeks after treatment). Durum wheat height was decreased as much as 5% with dicamba/ MCPA/mecoprop, 4% with pyrasulfotole/bromoxynil and 6% with fenoxaprop-pethyl/safener but was not affected with other herbicides evaluated. There was no decrease in durum wheat yield with the herbicides evaluated.

There is little information on the tolerance of dry bean to pendimethalin. Field studies were conducted in 2007 to 2009 at Exeter, Ontario and in 2008 and 2009 at Ridgetown, Ontario to evaluate tolerance of black, cranberry, kidney, otebo, pink, pinto, Small Red Mexican and white bean to the pendimethalin applied preplant incorporated at 1080 and 2160 g.a.i.ha-1. Pendimethalin PPI caused minimal injury in most market classes of dry bean at 1 and 2 WAE. There was no injury in various market classes of dry bean with the low dose at 1 and 2 weeks after emergence (WAE). However, at the high dose there was 0 to 4% injury at 1 WAE and 0 to 7% injury at 2 WAE in black, cranberry, kidney, otebo, pink, pinto, SRM and white bean. Pendimethalin PPI was more injurious in white bean than in black, cranberry, kidney, otebo, pink, pinto and SRM bean. Pink and SRM bean exhibited the most tolerance to pendimethalin applied PPI at 1080 g.ai.ha-1 or 2160 g.ai.ha-1. Pendimethalin caused no adverse effect on plant height, shoot dry weight, seed moisture content and seed yield of black, cranberry, kidney, otebo, pink, pinto, SRM and white bean. Based on these results, there is an adequate margin of crop safety for pendimethalin applied PPI at the proposed dose of 1080 g.ai.ha-1 in black, cranberry, kidney, otebo, pink, pinto, SRM and white bean in Ontario.

Volunteer adzuki bean within a corn crop can decrease corn yield and increase the adzuki bean seed bank. The objective of this research was to evaluate the efficacy of various preemergence (PRE) and postemergence (POST) herbicides for the control of volunteer adzuki bean [Vigna angularis (Willd.) Ohwi & Ohashi] in corn. Trials were conducted at two locations in 2005, 2006, 2007 and 2009. Experiments were arranged in a randomized complete block design with either seven PRE or ten POST herbicides. Volunteer adzuki bean interference resulted in corn yield losses of 16 to 43%. The PRE herbicides provided variable control. The highest and most consistent control PRE was provided by dicamba/atrazine, which provided 69 to 97% control of volunteer adzuki bean at 4 and 8 wk after emergence (WAE), respectively. Dicamba/atrazine PRE reduced volunteer adzuki bean density and biomass 67 to 97% 10 WAE. Generally, the POST herbicides evaluated provided better and more consistent control of volunteer adzuki bean than the PRE herbicides. Dicamba/atrazine applied POST provided greater than 95% control of volunteer adzuki bean and consistently reduced volunteer adzuki bean density and biomass to the equivalent of the weed-free control. Dicamba/atrazine applied POST resulted in corn yields equivalent to the weed-free control. The best option for controlling volunteer adzuki bean in corn is to apply dicamba/atrazine POST, while the remaining herbicides evaluated provided variable control.

Volunteer winter cereals are found sporadically in maize (Zea mays L.) fields across southern Ontario. Seven field trials were conducted over a two-year period (2006 and 2007) at four locations to determine the efficacy of five acetolactate synthase (ALS)-inhibiting herbicides for the control of volunteer cereals applied at two post-emergence application timings (2–4 and 4–7 maize leaf tips). The volunteer cereals were a hard red winter wheat (Triticum aestivum L.) (‘Hyland AC Morley’), soft red winter wheat (‘Pioneer 25R47’), soft white winter wheat (‘Pioneer 25W41’), and a autumn rye (Secale cereale L.) (‘FR’) cultivar. Volunteer cereal competition in maize resulted in a yield reduction of up to 44%. Foramsulfuron, nicosulfuron, nicosulfuron/rimsulfuron provided greater than 70% control of the volunteer cereals at 56 days after treatment (DAT), while primisulfuron and rimsulfuron provided greater than 60% control. Volunteer cereal control with early and late application was greater than 82 and 61%, respectively. Hard red winter wheat was the most sensitive to the ALS-inhibiting herbicides with control of 84–93%. Soft red and soft white winter wheat cultivars were intermediate in sensitivity with control of 76–87%, while autumn rye was the least sensitive with control of at 56–71% control at 56 DAT. Maize yields were improved when volunteer cereals were controlled with the use of herbicides compared to the weedy control, but were lower than the weed-free control. Early herbicide application resulted in improved control of volunteer cereals and higher maize yield.

Pendant trois ans (2005-2007), les auteurs ont effectue six essais sur le terrain pres d'Exeter et de Ridgetown (Ontario) afin d'evaluer la tolerance de trois sortes de ble d'hiver [tendre blanc (BHTB), tendre rouge (BHTR) et rouge vitreux (BHRV)] a trois taux de fluroxypyr additionne d'ester de MCPA (54+281,25, 108 + 562,5 et 216+1 125 g de matiere active par hectare) applique apres la levee (POST) a deux moments [Zadoks 31-32 (POST 1) et Zadoks 33-34 (POST 2)], au printemps. L'application de fluroxypyr additionne d'ester de MCPA a POST 1 n'endommage pas le ble d'hiver. L'application de fluroxypyr additionne d'ester de MCPA a POST 2 entraine respectivement jusqu'a 4, 4 et 7% de dommages au BHTB, BHTR et BHRV, 14 jours apres le traitement. L'application de fluroxypyr additionne d'ester de MCPA a raison de 54+281,25, 108+562,5 et 216+1 125 g de matiere active par hectare a POST 2 entraine respectivement jusqu'a 1, 6 et 10% de dommages, 14 jours apres le traitement. L'application de 216+ 1125 g de fluroxypyr additionne d'ester de MCPA par hectare (POST 2) entraine respectivement jusqu'a 5, 5 et 12% de dommages au BHTB, BHTR et BHRV. Le ble d'hiver mesurait en moyenne 3 cm de moins de hauteur consecutivement a l'application du taux le plus eleve de fluroxypyr additionne d'ester de MCPA, en 2006. Le taux ou le moment d'application du fluroxypyr additionne d'ester de MCPA n'a eu aucune incidence sur le rendement du ble d'hiver. Les auteurs en concluent qu'on dispose d'une marge de securite suffisante pour appliquer le fluroxypyr additionne d'ester de MCPA au ble d'hiver apres la levee au printemps.

Glyphosate-resistant (GR) cropping systems are popular and used extensively by producers. However, the long-term impacts of heavy reliance of this technology on weed community structure are not known. Five fully phased field experiments (two no-tillage and three conventional tillage) were established at four locations in southwestern Ontario where the effects of herbicide system (glyphosate or conventional) in corn and soybean and crop rotation (corn–soybean or corn–soybean–winter wheat) on midseason weed communities were examined. Multivariate analysis on data over the last 3 yr of the 6-yr experiment showed that weed communities were distinctly different among the treatments within each experiment. At several locations, midseason weed communities were more similar in corn and soybean treated with glyphosate compared to the same crops treated with conventional herbicides, reflecting the continuous application of the same selection pressure in both crops. Analysis of trait-densities revealed an increase in species with late initiation of seedling recruitment at the expense of weed species with medium time of initiation of seedling recruitment rather than early recruiting species. Increases in perennial species, species with a short interval between recruitment and anthesis, and wind-dispersed species were also observed. Trait-density–based analysis of the weed community was an effective method for reducing the complexity of divergent weed communities that enabled direct quantitative comparison of the herbicideinduced effects on these weed communities. Nomenclature: Glyphosate; corn, Zea mays L. ZEAMX; soybean, Glycine max (L.) Merr. GLXMA; winter wheat, Triticum aestivum L. TRZAW.

Deciding on the most efficacious PRE and POST herbicide options and their ideal application timing can be challenging for soybean producers. Climatic events during the 14 d before and after herbicide application can further complicate decisions because of their influence on herbicide effectiveness. Nine field trials were conducted at three locations in southwestern Ontario from 2003 to 2006, to determine the most effective PRE and POST soybean herbicides for control of common lambsquarters, common ragweed, green foxtail, and redroot pigweed. When precipitation was low at least 7 d before and after herbicide application weed control was reduced in treatments that included imazethapyr (PRE or POST) or flumetsulam/S-metolachlor (a premix formulation) (PRE). Cumulative precipitation during the 12 d after PRE application that exceeded the monthly average by at least 60% reduced common lambsquarters control when metribuzin was applied and green foxtail control when imazethapyr was applied. Delaying application of imazethapyr + bentazon to a later soybean growth stage decreased control of common lambsquarters and green foxtail; however, environmental conditions appeared to influence these results. Precipitation on the day of application decreased control of common ragweed and redroot pigweed more with quizalofop-p-ethyl + thifensulfuron-methyl + bentazon compared with imazethapyr + bentazon. Soybean yield varied among POST herbicide treatments because of reduced weed control. This research confirms that environmental conditions pre- and postapplication, as well as application timing, influence herbicide efficacy and should be considered by growers when selecting an herbicide program.

Six field trials were conducted over a 2-yr period (2004 and 2005) at Exeter and Ridgetown, ON, Canada, to evaluate the effect of postemergence application of rimsulfuron plus dicamba plus S-metolachlor/benoxacor, nicosulfuron/rimsulfuron plus dicamba/diflufenzopyr and nicosulfuron plus dicamba/diflufenzopyr with and without Agral 90® or Liberate® non-ionic surfactants on weed control and yield of corn. There was no difference between Agral 90® and Liberate® adjuvant in respect to control of velvetleaf, common ragweed, common lambsquarters and green foxtail. All herbicide treatments provided significantly higher yield than the untreated control. There was also no difference between Agral 90® and Liberate® in respect to corn yield when added to rimsulfuron plus dicamba plus S-metolachlor/benoxacor, nicosulfuron/rimsulfuron plus dicamba/diflufenzopyr and nicosulfuron plus dicamba/diflufenzopyr. Based on these results, Liberate® can be used as an alternative non-ionic surfactant for Agral 90® with the herbicides evaluated.Key words: Agral 90®, benoxacor, dicamba, diflufenzopyr, Liberate®, nicosulfuron, rimsulfuron, S-metolachlor, Zea mays L.

Poor survival of winter cereals due to winter conditions in Ontario can necessitate destruction of the stand in the spring to allow the subsequent seeding of an alternative crop. Winter cereals were seeded in the autumn of 2004 and 2005 at the Huron Research Station and at the University of Guelph Ridgetown Campus in Ontario to evaluate two formulations of glyphosate [potassium (K) vs diammonium (DA) salt] at different doses (225, 450, 675, 900, or 1350 g a.e. ha−1) for the burn-off of soft white winter wheat (SWW), soft red winter wheat (SRW), hard red winter wheat (HRW) and autumn rye (AR) in either late April or early May. There was no difference between the glyphosate formulations for the control of winter cereals at 1, 2, 3, and 4 weeks after treatment (WAT). There was generally improved control with glyphosate applications made in early May compared to late April however results were not always statistically significant. Generally, control of winter cereals increased as the glyphosate dose was increased from 225 to 1350 g a.e. ha−1. The minimum dose of glyphosate required for providing 90% or greater control of SWW, SRW, HRW, and AR was 675 g a.e. ha−1 at 4 WAT. Glyphosate applied at 675 g a.e. ha−1 caused a 98, 97, 98, and 99% reduction in shoot dry weight of SWW, SRW, HRW, and AR, respectively. Based on this study glyphosate (K or DA) applied in late April or early May can be used at doses as low as 675 g a.e. ha−1 to adequately control SWW, SRW, HRW, and AR in the spring.

Field experiments were conducted in 2003, 2006, and 2007 in Ontario to determine if reduced doses of imazethapyr combined with trifluralin applied pre-plant incorporated (PPI) can be used as an economically and environmentally feasible weed management strategy for broad spectrum weed control in white and kidney bean. There was minimal injury ( Setaria viridis (L.) Beauv. (green foxtail), Chenopodium album L. (common lambsquarters) and Ambrosia artemisiifolia L. (common ragweed) was reduced when combined with trifluralin (600 g ai ha −1 ). There was a trend for increased yield of white and kidney bean with increasing doses of imazethapyr applied alone and in combination with trifluralin. Combining trifluralin with imazethapyr increased the environmental impact (EI) by more than ten-fold compared to imazethapyr alone. The lowest dose of imazethapyr used in this study resulted in the lowest environmental risk. The doses of imazethapyr that maximized profit were 38 g ai ha −1 for white bean and 47 g ai ha −1 for kidney bean. Combining imazethapyr with trifluralin will provide growers with a weed management strategy that provides acceptable weed control, with only a small increase in environmental impact, and has the potential to increase yields and net returns.

The level of tolerance of various market classes of dry bean to cloransulam-methyl is not known. Three field studies were conducted in Ontario, Canada during 2007 and 2008 to determine the level of tolerance of black, cranberry, kidney, and white bean to the pre-emergence (PRE) and postemergence (POST) application of cloransulam-methyl at 17.5, 35, and 70 g ai ha−1. Cloransulam-methyl applied at 17.5, 35, and 70 g ha−1 caused between 13 and 23% injury in black, cranberry, kidney, and white bean, respectively. Cloransulam-methyl applied at 17.5, 35, and 70 g ha−1 reduced the shoot dry weight by between 16 and 28% compared to the untreated control. Cloransulam-methyl applied PRE reduced the height of black bean by 27% and the height of cranberry bean by 25% at 70 g ha−1 and reduced the height of white bean by 19% at 35 g ha−1 and by 37% at 70 g ha−1. Cloransulam-methyl applied PRE reduced the yield of black bean by 29% at 35 g ha−1 and by 43% at 70 g ha−1, reduced the yield of cranberry bean by 43% at 70 g ha−1, and reduced the yield of white bean by 36% at 35 g ha−1 and by 54% at 70 g ha−1. Based on these results, there is not an adequate margin of crop safety for the PRE and POST application of cloransulam-methyl in black, cranberry, kidney, and white bean at the rates evaluated.

Weed management options for adzuki-bean growers in Ontario, Canada are limited due to few herbicide registrations. Four field trials were conducted at three locations in south-western Ontario in 2007 and 2008 to determine the tolerance of adzuki bean to several preplant-incorporated (PPI), pre-emergence (PRE), and post-emergence (POST) herbicides. All the herbicides were applied at the doses registered for use in soybean. The application of pendimethalin, cloransulam-methyl, and halosulfuron-methyl (PPI), flumetsulam, cloransulam-methyl, and halosulfuron-methyl (PRE), and acifluorfen and fomesafen (POST) caused ≤15% crop injury; however, the injury was transient and did not reduce the adzuki bean yield. The POST application of cloransulam-methyl and imazethapyr caused ≤23% crop injury and reduced the biomass by ≤50%, but did not reduce the plant height or crop yield. Metribuzin, flumetsulam, atrazine, and pyroxasulfone (PPI), metribuzin, linuron, pyroxasulfone, and atrazine (PRE), and bentazon, imazethapyr plus bentazon, halosulfuron-methyl, and thifensulfuron-methyl (POST) caused ≤61% crop injury. These treatments reduced the biomass, plant height, and crop yield. Based on these results, pendimethalin, cloransulam-methyl, and halosulfuron-methyl applied PPI, flumetsulam, cloransulam-methyl, and halosulfuron-methyl applied PRE, and acifluorfen and fomesafen applied POST might be potential weed management options for weed management in adzuki bean. Cloransulam-methyl and imazethapyr applied POST will need further evaluation due to phytotoxicity concerns. Metribuzin, flumetsulam, atrazine, and pyroxasulfone applied PPI, metribuzin, linuron, atrazine, and pyroxasulfone applied PRE, and bentazon, imazethapyr plus bentazon, halosulfuron-methyl, and thifensulfuron-methyl applied POST did not have an adequate margin of safety.

Long-spine sandbur is an annual grass that infests many fields in southwestern Ontario, especially those with sandy soils. Eight field experiments were conducted over a 2-yr period (2007, 2008) in Ontario to determine the efficacy of various preemergence (PRE) and postemergence (POST) herbicides for control of long-spine sandbur in corn. Generally, the POST applied herbicides controlled long-spine sandbur better than PRE herbicides evaluated in this study. PRE application of dimethenamid-p (1250 g a.i. ha-1), S-metolachlor (1600 g a.i. ha-1), flufenacet (1040 g a.i. ha-1), pendimethalin (1680 g a.i. ha-1), pyroxasulfone (250 g a.i. ha-1), or isoxaflutole plus atrazine (105 + 1063 g a.i. ha-1) controlled long-spine sandbur 0-79%. POST application mesotrione + atrazine (140 + 280 g a.i. ha-1) or topramezone + atrazine (18.75 + 500 g a.i. ha-1) provided 24-82% control, foramsulfuron (35 g a.i. ha-1) or primisulfuron/dicamba (26 +140 g a.i. ha-1) provided 54-87% control, and rimsulfuron (15 g a.i. ha-1), nicosulfuron (25 g a.i. ha-1) or nicosulfuron/rimsulfuron (25 g a.i. ha-1) provided 68-95% control of long-spine sandbur in corn. Similar reduction in sandbur density and shoot dry weight were observed. PRE applied isoxaflutole + atrazine and POST applied rimsulfuron, nicosulfuron, nicosulfuron/rimsulfuron, foramsulfuron, primisulfuron/dicamba, and topramezone + atrazine all provided yield comparable with the weed-free control. Among the herbicides evaluated rimsulfuron, nicosulfuron, and nicosulfuron/rimsulfuron provide the most consistent long-spine sandbur control in corn.Key words: Weed control, preemergence herbicide, postemergence herbicide, rimsulfuron, nicosulfuron, foramsulfuron, primisulfuron, dicamba, topramezone, atrazine

Eight field trials were conducted over a 3-yr period at Exeter (one site in 2005 and 2006) and Ridgetown (three sites in 2005, two sites in 2006 and one site in 2007), Ontario, to evaluate different postemergence glyphosate tank mixes for weed management in glyphosate-tolerant corn. Treatments included a weedy check, a single application of glyphosate, a sequential application of glyphosate and tank mixes of glyphosate plus either atrazine, dicamba/atrazine, mesotrione, s-metolachlor plus atrazine, s-metolachlor/atrazine, dicamba/diflufenzopyr, and dimethenamid plus atrazine. A single application of glyphosate, the sequential application of glyphosate and tank mixes of glyphosate plus either atrazine, dicamba/atrazine, mesotrione, s-metolachlor plus atrazine, s-metolachlor/atrazine, dicamba/diflufenzopyr, and dimethenamid plus atrazine provided 92-100% control of redroot pigweed, 87-100% control of common ragweed, 74-100% control of common lambsquarters, and 43-100% control of green foxtail. All herbicide treatments had a higher yield than the weedy check. There were no differences in corn yield among the herbicide treatments evaluated. The glyphosate alone or in tank mix combination with mesotrione or dicamba/diflufenzopyr programs had the lowest environmental impact. Glyphosate plus atrazine and dicamba/diflufenzopyr were the most profitable weed management programs in glyphosate-tolerant corn.Key words: Atrazine, dicamba, diflufenzopyr, dimethenamid, glyphosate, mesotrione, pendimethalin, rimsulfuron, s-metolachlor, Zea mays L.

Five field trials were conducted over a 2-yr period (2007, 2008) at various locations in Ontario to evaluate the tolerance of black, cranberry, kidney, otebo, pink, pinto, small red Mexican (SRM), and white bean to halosulfuron applied PPI, PRE, and POST at 35 and 70 g ai/ha. There was minimal injury (3% or less) with halosulfuron applied PPI or PRE in dry bean. At Exeter and Ridgetown, halosulfuron applied POST at 35 and 70 g/ha caused 3 to 5% and 4 to 8% injury in dry bean, respectively at 1 wk after herbicide application (WAA). The injury was transient with no significant injury at 2 and 4 WAA. At Harrow, halosulfuron POST at 35 and 70 g/ha caused as much as 4% injury at 35 g/ha and 14% injury at 70 g/ha in dry bean. Halosulfuron applied PPI, PRE, and POST at 35 and 70 g/ha caused no decrease in plant height of dry bean except for kidney bean, which was reduced 6% at 70 g/ha, and white bean, which was reduced 3% at both 35 and 70 g/ha. Halosulfuron applied PPI, PRE, and POST at 35 and 70 g/ha caused no decrease in dry bean yield except for kidney bean, which was reduced 9% at 35 g/ha and 10% at 70 g/ha; otebo bean, which was reduced 3% at 70 g/ha; and white bean, which was reduced 7% at both 35 and 70 g/ha. On the basis of these results, there is an adequate margin of crop safety in dry bean to halosulfuron applied PPI or PRE at 35 and 70 g/ha. In addition, there is an adequate margin of crop safety in black, cranberry, pink, pinto, and SRM bean to halosulfuron applied POST at 35 and 70 g/ha. However, further research is required to ascertain the tolerance of kidney, otebo, and white bean to halosulfuron applied POST.

Glyphosate-resistant (GR) crops have been adopted rapidly since their commercial introduction, and with the increase in commercially available crops resistant to glyphosate, continuous use of the same herbicide mode of action is now possible in some crop rotations. A 6-yr study was initiated to investigate the effects of conventional herbicides compared with continuous use of glyphosate in GR or Roundup Ready corn and GR soybean in a corn–soybean and a corn–soybean–winter wheat rotation. Individual experiments were fully phased and established at three locations under conventional tillage (CT) and at two locations under no-tillage (NT). Results indicated that midseason weed ground cover was lower when weeds were controlled with glyphosate; however, in most cases, this did not result in improved corn or soybean yields. Within locations, species richness, which strongly influenced other diversity indicators, was most affected by the herbicide treatments. Including winter wheat in the crop rotation had little effect on corn and soybean weed ground cover, density, and community structure and only affected soybean yield. Moreover, no effects of herbicide system used in previous corn and soybean were observed in winter wheat, with the exception of species diversity in NT, where species diversity tended to be greater when weeds in previous corn and soybean were treated with conventional herbicides. After 6 yr, the effects of continuous use of GR crops in rotation were similar to those reported in previous studies; however, continued monitoring and longer-term investigations of these systems are necessary to detect the early stages of development of herbicide-resistant biotypes.

Five field trials were conducted over a three-year period (2006–2008) at two locations in southwestern Ontario to determine the length of time herbicides can remain in the spray tank prior to application in the field without impacting efficacy. Four pre-emergence and five post-emergence herbicides were mixed at their labelled rates and then applied in maize. Herbicides were either applied immediately after mixing in water, or after being held in solution for 1, 3 or 7 days. The most common weed species in the trials were Abutilon theophrasti, Amaranthus retroflexus, Ambrosia artemisiifolia, and Chenopodium album. Holding the herbicides in spray solution for up to 7 days did not affect the efficacy of the post-emergence herbicides in this study. Similarly, control of A. retroflexus and C. album with the pre-emergence herbicides was not affected holding the herbicides in spray solution for up to 7 days. However, control of A. theophrasti was decreased when isoxaflutole plus atrazine, dimethenamid plus dicamba/atrazine, or rimsulfuron plus S-metolachlor plus dicamba was in spray solution for more than 1 day. Nonetheless, there were no decreases in yield for any of the treatments evaluated. These data provide valuable information which growers can use to make informed decisions on whether to apply herbicides in non-ideal weather or to postpone application. The results of this study suggest that for the herbicides and weed species tested it is better to postpone application rather than make applications under non-ideal conditions.

Three field trials were conducted over a 2-yr period at Exeter (2007, 2008) and Ridgetown (2007), Ontario to evaluate the tolerance of two market classes and two cultivars of each market class (cranberry, Etna and Hooter; kidney, Red Kanner and Red Hawk) of dry bean to preplant incorporated (PPI) and preemergence (PRE) applications of pyroxasulfone at 209 and 418 g a.i. ha-1. All treatments including the non-treated control were maintained weed free during the growing season. There was greater injury when pyroxasulfone was applied PPI than PRE, and injury was greater with the high rate at 1, 2, and 4 wk after emergence (WAE). Pyroxasulfone at 209 and 418 g a.i. ha-1 caused as much as 32 and 61% visible injury when applied PPI and 15 and 30% visible injury when applied PRE in dry bean, respectively. Pyroxasulfone at 209 and 418 g a.i. ha-1 decreased shoot dry weight as much as 60 and 80% when applied PPI and 30 and 50% when applied PRE in dry bean, respectively. Plant height was not affected by pyroxasulfone application timing, but was rate dependent. Height was reduced 14, 13, 22 and 13% at 209 g a.i. ha-1 and 24, 31, 42 and 27% at 418 g a.i. ha-1 for Etna, Hooter, Red Kanner and Red Hawk cultivars, respectively. Dry bean yield was reduced as much as 29% at 209 g a.i. ha-1 and 45% at 418 g a.i. ha-1. This research shows that there is not an adequate margin of crop safety for pyroxasulfone applied PPI or PRE at the rates evaluated in Etna, Hooter, Red Kanner and Red Hawk dry beans in Ontario.Key words: Cranberry bean, Etna bean, kidney bean, Hooter bean, Phaseolus vulgaris L., Red Hawk bean, Red Kanner bean, pyroxasulfone

There is limited information on the tolerance of various market classes of dry bean to the soil application of fomesafen alone or in tank mix combination with S-metolachlor. Field trials were conducted in Ontario over a two year period (2006 and 2007) to evaluate the tolerance of black, cranberry, kidney, and white (navy) bean to the pre-plant incorporated (PPI) and pre-emergence (PRE) application of S-metolachlor and fomesafen alone and in tank mix combination. Treatments included a non-treated check. All treatments were maintained weed free during the growing season. Visible injury differed among the four market classes of dry bean at 14 days after emergence. Visible injury was generally greater in the smaller seed market classes (black and white bean) compared to the larger seeded market classes (kidney and cranberry bean). Visible injury seen in some market classes of dry bean early in the season was minimal and transitory and caused no adverse effects on plant height, shoot dry weight, seed moisture content, and yield. Based on these results, S-metolachlor and fomesafen alone and in combination applied PPI or PRE at the proposed maximum use dose can be safely used for weed management in black, cranberry, kidney, and white bean production in Ontario.

Saflufenacil (BAS 800H) is a new herbicide being developed by BASF for PRE broadleaf weed control in corn. Field studies were conducted at two Ontario locations in 2006 and 2007 to evaluate the tolerance of field corn to PRE and POST (spike and two- to three-leaf corn) applications of saflufenacil at 50, 100, and 200 g ai/ha with and without an adjuvant (surfactant blend + solvent [petroleum hydrocarbons]; 1% v/v). Saflufenacil applied PRE reduced corn height by as much as 12% with the highest rate of 200 g/ha; however, corn yield was not affected. When saflufenacil was applied without an adjuvant to corn at the spike stage, injury was as much as 12%, 7 d after treatment (DAT). However, corn height and yield were not affected. Saflufenacil applied POST to two- to three-leaf corn at 50 to 200 g/ha without an adjuvant resulted in as much as 25% injury and reduced corn height 31% but did not affect yield. Adding an adjuvant to POST applications of saflufenacil caused as much as 4 and 99% injury, reduced corn height 13 and 77%, and reduced corn yield 0 and 59% when applied to corn at the spike and at the two- to three-leaf stages, respectively. Based on these results, saflufenacil applied PRE can be safely used in corn at rates up to 200 g/ha. Saflufenacil applied to corn at the spike and two- to three-leaf stage at 50 or 100 g/ha without an adjuvant demonstrated acceptable corn tolerance and may allow for the use of saflufenacil beyond the proposed PRE use pattern. In contrast, applying saflufenacil POST with an adjuvant to spike and two- to three-leaf stage corn resulted in unacceptable injury and yield losses in field corn.

Field trials were conducted from 2005 to 2007 at two locations in southwestern Ontario to investigate how weed control in corn was affected by the time of day that herbicides were applied. Weed control following the application of six POST herbicides (atrazine, bromoxynil, dicamba/diflufenzopyr, glyphosate, glufosinate, and nicosulfuron) at 06:00, 09:00, 12:00, 15:00, 18:00, 21:00, and 24:00 h was assessed. For many weed species herbicide efficacy was reduced when applications were made at 06:00, 21:00, and 24:00 h. Velvetleaf was the most sensitive to the time of day effect, followed by common ragweed, common lambsquarters, and redroot pigweed. Annual grasses were not as sensitive to application timing; however, control of barnyardgrass and green foxtail was reduced in some environments at 06:00 h and after 21:00 h. Only in the most severe cases was the grain yield of corn reduced due to decreased weed control. Daily changes in air temperature, relative humidity, and light intensity that cause species-specific physiological changes may account for the variation in weed control throughout the day. The results of this research suggest that there is a strong species-specific influence of ambient air temperature, light intensity, and leaf orientation on the efficacy of POST herbicides. These results should aid growers in applying herbicides when they are most efficacious, thus reducing costs associated with reduced efficacy.

A study was conducted over a 3-yr period (2003, 2004, and 2005) to evaluate the effect of reduced herbicide rates - 20, 40, 60, 80, and 100% of the manufacturer’s recommended rate (MRR) - on weed biomass reduction, environmental impact (EI), yield, and profitability of corn (Zea mays L.) in Ontario. The herbicide rate required to provide 95% biomass reduction of velvetleaf (Abutilon theophrasti Medic.), redroot pigweed (Amaranthus retroflexus L.), common ragweed (Ambrosia artemisiifolia L.), common lambsquarters (Chenopodium album L.), and annual grasses was 92, 30, 41, 28, and 83% of the MRR for isoxaflutole plus atrazine, >200, 119, 23, 23, and 117% of the MRR for dimethenamid plus dicamba/atrazine, 141, 72, 46, 45, and >200% of the MRR for glufosinate plus atrazine, and 81, 29, 18, 24, and 88% of the MRR for nicosulfuron/rimsulfuron plus dicamba/diflufenzopyr, respectively. The herbicide rate required to provide 95% of weed-free corn yield was 61, 22, 130, and 11% of the MRR for isoxaflutole plus atrazine, dimethenamid plus dicamba/atrazine, glufosinate plus atrazine, and nicosulfuron/rimsulfuron plus dicamba/diflufenzopyr, respectively. Nicosulfuron/rimsulfuron plus dicamba/diflufenzopyr had the lowest EI. The results of profitability analysis suggested that the MRR rates do not tend to maximize profit margins. In most cases, there were no significant differences in profit margins for treatments with 40, 60, 80, and 100% of the MRR. Key words: Atrazine, dicamba, diflufenzopyr, dimethenamid, glufosinate, nicosulfuron, rimsulfuron, Zea mays L.

Five field experiments were conducted in 2007 to determine the effect of simulated dicamba/diflufenzopyr drift followed by postemergence applications of chlorimuron-ethyl, imazethapyr or bentazon on soybean (Glycine max Merr.) crop injury, dry weight, height and yield. In the absence of a postemergence herbicide, as the dose of simulated dicamba/diflufenzopyr increased there was an increase in soybean injury and a decrease in dry weight, height and yield. The application of registered postemergence herbicides following simulated dicamba/diflufenzopyr drift resulted in a synergistic increase in crop injury in some environments. There was no synergistic response in respect to dry weight and height when simulated drift was followed by postemergence herbicides. A synergistic yield response was observed with yield being decreased 4–7% more than expected due to simulated dicamba/diflufenzopyr drift followed by the application of chlorimuron-ethyl. No synergistic yield response was observed for dicamba/diflufenzopyr drift followed by either imazethapyr or bentazon.

Dry bean producers in Ontario, Canada, have few herbicide options available for annual broad-leaved weed management and there is little information on the tolerance of dry bean to linuron. The tolerance of black, cranberry, kidney, and white bean to the pre-emergence (PRE) application of linuron at the rates of 0, 500, 1000, 1500, 2000, and 2500 g ai ha⁻¹ was evaluated in field studies conducted in 2005 and 2006 at Exeter and in 2006 at Ridgetown, Ontario. The four market classes differed in their response to linuron. Cranberry and kidney bean were more tolerant to the PRE application of linuron than black and white bean. Linuron applied PRE caused as much as 12% injury in cranberry and kidney bean, 47% injury in black bean, and 56% injury in white bean. Linuron applied PRE at 500-2500 g ai ha⁻¹ had no effect on the height of cranberry and kidney bean but decreased the height by 7, 8, and 15% in black bean and by 10, 13, and 23% in white bean at 1500, 2000, and 2500 g ai ha⁻¹, respectively. Linuron applied PRE at the rates evaluated did not cause any adverse affect on the yield of cranberry, kidney, and white bean but black bean yield was reduced by 16% at 2500 g ai ha⁻¹. Based on these results, there is not an adequate margin of crop safety for the PRE application of linuron in black and white bean at rates >1000 g ai ha⁻¹. However, there is a potential for the use of linuron PRE for weed management in cranberry and kidney bean at the rates evaluated.

Field experiments were established at the Huron Research Station and at the University of Guelph Ridgetown Campus in the autumn of 2004 and 2005 to evaluate the tolerance of winter wheat to tankmixes of glyphosate plus either amitrole, dicamba, dicamba/diflufenzopyr, 2,4-D amine, 2,4-D ester, chlorimuron-ethyl or thifensulfuron-methyl/tribenuron-methyl applied either preplant (PP) or preemergence (PRE). Contrasts comparing PP vs PRE treatments showed no difference in visible injury, plant height and yield between application timings. The tankmixes of glyphosate (1800 g ha −1 ) plus either amitrole (1155 g ha −1 ), dicamba (300 g ha −1 ), 2,4-D amine (700 g ha −1 ), 2,4-D ester (700 g ha −1 ) or thifensulfuron-methyl/tribenuron-methyl (15 g ha −1 ) caused minimal (less than 6%) and transient visible injury in winter wheat. In addition, these tankmixes had no effect on plant height and yield. The tankmix of glyphosate (1800 g ha −1 ) with dicamba/diflufenzopyr (200 g ha −1 ) or chlorimuron-ethyl (9 g ha −1 ) caused as much as 8 and 18% visible injury in winter wheat, respectively. Glyphosate (1800 g ha −1 ) plus dicamba/diflufenzopyr (200 g ha −1 ) did not affect plant height but glyphosate plus chlorimuron-ethyl reduced plant height 11%. Yield was reduced 15% when glyphosate was tankmixed with dicamba/diflufenzopyr and 26% when glyphosate was tankmixed with chlorimuron-ethyl.

Summary 1. Genetically modified (GM), herbicide-tolerant crops have been adopted extensively worldwide, resulting in increased homogenization of agricultural practices. However, several countries still view GM crops with trepidation, citing potential risks to human health and the environment. We currently know little about how non-target biota responds to cultivation of GM crops under field conditions. 2. This study describes a series of microcosm and field experiments in Ontario, Canada, that estimated the effects of transgenic, glyphosate-tolerant (GT) crops and their management on the abundances of detritivorous soil biota and crop litter decomposition. 3. Absolute abundance of few of the measured biotic groups were affected by either the herbicide or variety treatments and, where significant effects were observed, the responses were not consistent across all years or for all sample dates within a year. More frequently, but not consistently, the GT herbicide system was associated with increased fungal : bacterial biomass ratios, suggesting a state of reduced enrichment. 4. Although the conventional and GT varieties studied differed in composition, we observed few effects of the modification for glyphosate-tolerance on maize Zea mays and soybean Glycine max litter decomposition. Overall, the herbicide system associated with GT crops reduced soybean- and corn-litter decomposition, but responses were inconsistent across Ontario, with many trials demonstrating no effect. Effects were probably underrepresented in this study as average daily precipitation was positively correlated with the magnitude of this system effect and many sites received well-below average levels of precipitation. 5. Synthesis and applications. Most concerns regarding the potential impacts of GM crops on non-target biota have targeted traits associated with the biotechnology itself. However, shifts in management practices associated with biotechnology are also widespread and have the same, if not greater, potential to alter the structure and functioning of agroecosystem biodiversity. The lack of observed permanent negative effects on soil biota in this study is heartening; however, more research is required to determine the functional consequences of observed transient effects and effects on other biota, as well as how altered crop litter decomposition affects agroecosystem nutrient cycling and carbon sequestration.

There have been anecdotal accounts of increased crop sensitivity due to herbicide drift followed by an in-crop herbicide. An experiment was conducted from 2005 to 2007 at Elora, Ridgetown, and Woodstock, Ontario, to determine the effects of simulated mesotrione drift followed by in-crop applications of glyphosate, imazethapyr, bentazon and glyphosate plus chlorimuron on glyphosate-resistant soybean [Glycine max (L.) Merr.] visual injury, plant height, plant density, shoot dry weight, and seed yield. As the rate of simulated mesotrione drift increased, there was an increase in soybean injury and a decrease in shoot dry weight, height, and yield. Simulated mesotrione drift followed by bentazon resulted in synergistic responses in injury shortly after application in some environments. This increase in injury was transient, with no synergistic responses in density, shoot dry weight, and yield. In contrast, antagonistic responses were observed when glyphosate, imazethapyr, or glyphosate plus chlorimuron were applied after simulated mesotrione drift in some environments. Further research is required to develop a better understanding of the interactions of drift followed by the application of an in-crop herbicide. Key words: Bentazon, chlorimuron, glyphosate, imazethapyr, mesotrione, synergism

Thirteen field experiments were conducted in Illinois, Indiana, Ohio, and Ontario from 2005 to 2007 to determine the effects of simulated glyphosate drift followed by in-crop applications of nicosulfuron/rimsulfuron plus dicamba/diflufenzopyr or foramsulfuron plus bromoxynil plus atrazine on nontransgenic corn injury, height, stand count, shoot dry weight, and yield. Simulated glyphosate drift at 100 and 200 g/ha, resulted in 11 to 61% visual crop injury and a 19 to 45% decrease in corn height. Simulated glyphosate drift at 200 g/ha caused a reduction in shoot dry weight by 46%, stand count by 28% and yield by 49 to 56%. Generally, simulated glyphosate drift followed by the in-crop herbicides resulted in an additive response with respect to visual crop injury, height, stand count, shoot dry weight, and yield. Nomenclature: Atrazine; bromoxynil; dicamba/diflufenzopyr; foramsulfuron; glyphosate; nicosulfuron/rimsulfuron; corn, Zea mays L

Plant competition is thought to be driven by limiting resources. We propose that plant competition is triggered initially by the red to far-red light ratio (R:FR) originating from neighbouring plants, followed by a series of complex physiological processes, which exclude direct resource competition. Field experiments were conducted in 2005 and 2006 in which maize (Zea mays) was grown hydroponically. The effect of R:FR signal being reflected from the leaf surface of Amaranthus retroflexus was isolated by avoiding direct competition for light, water and nutrients. Results showed that the low R:FR reflected from the leaf surface of A. retroflexus did alter the carbon allocation pattern of maize when compared with maize growing free of weeds. Prior to silking, maize grown under low R:FR experienced temporal changes in plant height, persistent changes throughout the sampling period in root and shoot dry weights and rate of leaf appearance, but no changes in leaf area. At silking, low R:FR reduced ear and total plant dry weight. These results support the hypothesis that changes in R:FR acts as an early signal of pending competition by initiating a shade avoidance response. Data from this experiment suggest that once a plant is physiologically triggered into a shade avoidance response, these plants do so at a physiological cost, which may constrain plant development and possibly reduce reproductive fitness.

An experiment was conducted in 2005 and 2006 in southwestern Ontario to examine the efficacy of imazethapyr application timing on the control of long-spined sandbur in soybean (Glycine max L. Merr.). Imazethapyr (100 g a.i. ha-1) was applied early and delayed preemergence (PRE), and postemergence (POST) at the spike to five-leaf stage of the weed. Soybean was not injured by any treatment. Imazethapyr applied PRE did not control long-spined sandbur; POST treatments resulted in up to 72, 66, 78, 91, 78, and 71% weed control when applied at the spike, one-, two-, three-, four-, and five-leaf stage, respectively, and crop yield increased 44, 28, 39, 24, 38, and 20%, respectively. Therefore, imazethapyr should be applied at the three-leaf stage of the weed to optimize control and crop yield. Key words: Weed control, soybean, preemergence herbicide, postemergence herbicide

Common waterhemp (Amaranthus tuberculatus) is an aggressive annual broadleaf whose distribution is expected to increase rapidly in agricultural land in eastern Canada. Eight field experiments (four in corn and four in soybean) over a 2-yr period (2005 and 2006) were established on two Ontario farms (near Comber and Petrolia, Ontario) with waterhemp infestations to evaluate the efficacy of various PRE- and POST-emergence herbicides applied alone or in sequence for the control of waterhemp in corn and soybean. There was minimal injury (up to 3.8%) to corn and soybean from the herbicide treatments evaluated. In corn, sequential herbicide programs of isoxaflutole + atrazine PRE fb either dicamba POST, dicamba/diflufenzopyr POST, dicamba/atrazine POST or mesotrione + atrazine POST provided consistent full-season control of waterhemp. Corn yield was reduced 48% when waterhemp was not controlled. Corn yield was equivalent to the weed-free check with the herbicide treatments evaluated. In soybean, PRE or POST herbicides alone provided 41 to 94% control of waterhemp, however, waterhemp control was increased to 90 to 99% with the sequential herbicide programs. Dimethenamid (PRE; 1250 g ha-1) followed by glyphosate (POST1; 900 g ha-1) followed by glyphosate (POST2; 900 g ha-1) controlled waterhemp 99%. Results with waterhemp density and biomass were similar to visible control. Soybean yield was reduced 41% when waterhemp was not controlled. Soybean yield was equivalent to the weed-free check with all the herbicide treatment except dimethenamid PRE, acifluorfen POST1 and fomesafen POST1 where the yield was 30, 19, and 19% lower, respectively. Key words: Waterhemp, weed control, glyphosate, corn, soybean, pre-emergence herbicide, post-emergence herbicide

Imazamox plus bentazon has the potential to provide broad spectrum weed control in dry bean ( Phaseolus vulgaris L.). Field trials were conducted in Ontario over a two year period (2003 and 2006) to evaluate the effect of imazamox plus bentazon applied post-emergence at 25 + 600 and 50 + 1200 g ai ha −1 on black, brown, cranberry, kidney, otebo, pinto, white and yellow eye beans. Treatments included a non-treated check. All treatments were maintained weed free during the growing season. The eight market classes responded similarly to imazamox plus bentazon. Imazamox plus bentazon applied post-emergence caused less than 4% visible injury at 7, 14 and 28 days after treatment. Imazamox plus bentazon applied post-emergence did not have any effect on plant height, shoot dry weight, seed moisture content and yield of dry bean. Based on these results, imazamox plus bentazon at the proposed maximum use dose can be safely used for weed management in black, brown, cranberry, kidney, otebo, pinto, white and yellow eye bean production in Ontario. Additional research is needed to determine if cultivars within a market class of dry bean differ in their response to imazamox plus bentazon.

There is little information available on performance interactions for tank mixtures of topramezone and acetolactate synthase (ALS)-inhibiting herbicides. Controlled-environment and field experiments were conducted in 2006 and 2007 to determine the interactions of topramezone when tank-mixed with ALS-inhibiting herbicides. Controlled-environment experiments were conducted on four annual grass species treated at the five- to six-leaf stage. Dose–response curves for large crabgrass, barnyardgrass, yellow foxtail, and green foxtail were generated for nicosulfuron or foramsulfuron alone and in combination with label rates of topramezone or mesotrione (with or without atrazine). Eight field experiments were conducted using registered rates of two ρ-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting and three ALS-inhibiting herbicides alone and in combination. All herbicide treatments in the field were applied at the two- to three-leaf and five- to six-leaf stages of barnyardgrass, green foxtail, giant...

Field trials were conducted in 2006 and 2007 on three Ontario farms with heavy infestations of cocklebur to determine the effectiveness of various preemergence (PRE) and postemergence (POST) herbicides for control of cocklebur in soybean [Glycine max (L.) Merr.]. There was minimal injury (2% or less) to soybean from the PRE and POST herbicides evaluated. Cloransulam applied PRE provided up to 98% visual control, reduced density 93%, and reduced dry weight of cocklebur 96%. Linuron, metribuzin, imazethapyr, and clomazone applied PRE provided 0 to 77% control and reduced density and dry weight of cocklebur minimally (54% or less) compared with the weedy check. Cloransulam applied POST provided as much as 98% control, reduced density up to 96%, and reduced dry weight of cocklebur as much as 98%. Chlorimuron, imazethapyr, imazethapyr plus bentazon, and glyphosate applied POST provided 49 to 90% control, reduced density 62 to 89%, and reduced dry weight of cocklebur 69 to 92%. Acifluorfen, fomesafen, bentazon, and thifensulfuron applied POST provided 1 to 51% control, reduced density 0 to 80%, and reduced dry weight 0 to 74% compared with the weedy check. Soybean yield increased as much as 79% compared with the weedy check as a result of cloransulam applied PRE or POST. Based on these results, cloransulam applied PRE or POST provides excellent control of cocklebur in soybean. Key words: Cocklebur, weed control, soybean, preemergence herbicide, postemergence herbicide

Two greenhouse trials were conducted over a 2 year period (2004 and 2005) to compare the relative growth potential and fitness of triazine-susceptible (TS) and triazine-resistant (TR) waterhemp biotypes. Waterhemp plants from each biotype were grown in 6 L pots in the greenhouse in a completely randomized design. There was no difference in leaf number, plant height, plant biomass, time to bud or time to flower between the two biotypes. The TR female waterhemp plants produced 30% less reproductive biomass and 39% less seed than the TS biotype. The fitness penalty associated with triazine resistance was related to reproductive capability, not to vegetative growth.

There is limited information on the effect of amitrole and 2,4-D ester applied preplant and pre-emergence in soybean (Glycine max L.) in Ontario, Canada. Six field trials were conducted over a 2 year period (2004 to 2005) at three Ontario locations to evaluate the response of soybean to amitrole or 2,4-D ester applied at 14 days preplant (DPP), 7 DPP, 1 day after planting (DAP), and 7 DAP. The application of amitrole resulted in as much as 5.8, 3.9, 1.7, and 1% visible crop injury in soybean at 7, 14, 28, and 56 days after emergence (DAE), respectively. There was no visible injury in soybean with any amitrole treatment at 56 DAE, except for amitrole applied at 7 DAP, which caused 1% visible injury in soybean at 2310 g ha−1. The application of the 2,4-D ester caused ≤8.3, 9.7, 4.6, and 1.3% visible injury in soybean at 7, 14, 28, and 56 DAE, respectively. The visible injury decreased over time. There was no visible injury in soybean with any of the 2,4-D ester treatments at 56 DAE, except for the 2,4-D ester treatment applied at 7 DAP, which caused 1% visible injury at 1155 g ha−1 and 1.3% visible injury at 2310 g ha−1. Soybean generally responded similarly to amitrole and 2,4-D ester when applied at 14 and 7 DPP; however, soybean was more tolerant to amitrole compared to 2,4-D ester when applied at 1 or 7 DAP. The application of amitrole and 2,4-D ester resulted in no biomass or yield reduction in soybean compared to the weed-free, untreated control at all doses and application timings evaluated. Soybean is tolerant to the preplant and pre-emergence application of amitrole or 2,4-D ester at the doses evaluated.

A study was conducted over a 3-yr period (2004–2006) in Ontario to evaluate various weed management programs in white bean (Phaseolus vulgaris L.). Herbicide treatments evaluated caused no visible injury in white bean. Trifluralin provided 12% (percentage points) greater control of common lambsquarters (Chenopodium album L.) than s-metolachlor. There was no benefit of tank-mixing s-metolachlor and trifluralin for yield and profitability compared with either trifluralin or s-metolachlor alone. The postemergence (POST ) application of bentazon plus fomesafen following a soil-applied herbicide resulted in improved control of common lambsquarters by 15%. Two inter-row cultivations following a soil-applied herbicide resulted in improved control of redroot pigweed (Amaranthus retroflexus L.), common lambsquarters, and green foxtail [Setaria viridis (L.) Beauv.]. The addition of imazethapyr (60% of label dose; 45 g a.i. ha-1) to the soil-applied herbicide resulted in improved control of redroot pigweed (+6%), common lambsquarters (+16%), and green foxtail (+6%). The profit margin tended to increase if more than just a grass preplant-incorporated (PPI) herbicide was used. The best profit margin was with a grass PPI herbicide alone plus cultivation. The profit margin also tended to increase with the use of cultivation rather than a broadleaf POST herbicide. Key words: Bentazon, cultivation, fomesafen, imazethapyr, navy bean, s-metolachlor, trifluralin, Phaseolus vulgaris L.

A study was conducted at three locations in central-southwestern Ontario from 1996 to 1998 to determine if corn (Zea mays L.) productivity and weed control can be maintained when row spacing is narrowed, crop density is increased and herbicide rate is reduced. Post-emergence herbicides [(rimsulfuron + nicosulfuron) plus (dicamba + atrazine)] at four rates (full label rate (1×), 75% full rate (0.75×), 50% full rate (0.5×) and an untreated check) were tested at three corn row-spacings (38, 50, and 75 cm) and two plant densities (75 000 and 90 000 plants ha-1). Herbicide application at the 0.5× rate versus an untreated check still allowed for increased corn yield (8.3 vs. 4.9 t ha-1) and decreased weed dry weight (9.4 vs. 240.4 g m-2), weed plant density (11.0 vs. 52.6 plants m-2) and weed seed density (239 vs. 14 241 seeds m-2). Corn LAI was not affected by decreasing herbicide rate. In this study, increasing corn plant density and decreasing corn row spacing were not factors in reducing herbicide inputs in corn cropping systems in central-southwestern Ontario. Herbicide rate could be reduced by up to 50% while maintaining corn grain yield, weed density, weed dry weight, and the number of weed seeds entering into the soil seed bank. Implementation of these reduced rates will help to increase the economic and environmental sustainability of the Canadian field corn industry. Key words: Agricultural systems, crop yield, seeding rate, sustainability, weed biomass

Fifteen field experiments were conducted from 2002 to 2005 to determine the influence of the nozzle type, spray volume, spray pressure, and herbicide rate on herbicidal efficacy in soybean. There was no effect of the nozzle type on herbicidal efficacy with fomesafen, bentazon, glyphosate, and cloransulam-methyl when applied at the manufacturer's recommended rate. The control of Echinochloa crus-galli (barnyardgrass) with quizalofop-p-ethyl was improved when applied with flat fan (FF) nozzles compared with air induction (AI) nozzles. There was an increase in weed control with the FF nozzles compared with the AI nozzles in four of the 13 comparisons when the herbicides were applied at half the recommended rate, while in two situations, application with the AI nozzles resulted in improved weed control. With the FF nozzles, there was no effect of the water carrier volume on weed control with bentazon, glyphosate, and cloransulam-methyl. The control of Abutilon theophrasti (velvetleaf) and Chenopodium album (common lambsquarters) with fomesafen and E. crus-galli with quizalofop-p-ethyl was improved at the higher water carrier volume. With the AI nozzles, the control of A. theophrasti and Ambrosia artemisiifolia (common ragweed) with fomesafen and E. crus-galli with quizalofop-p-ethyl was improved at the higher water carrier volume, while the control of A. theophrasti and Polygonum persicaria (ladysthumb) was improved with glyphosate at the lower water carrier volume. With the AI nozzles, the control of C. album with bentazon and E. crus-galli with quizalofop-p-ethyl was improved at the higher spray pressure. There was no effect of the nozzle type on the soybean yield with glyphosate, cloransulam-methyl, and quizalofop-p-ethyl. The use of the FF nozzles compared with the AI nozzles to apply fomesafen and bentazon increased the soybean yield by 6 and 7%, respectively. Based on this study, the optimum nozzle type, water carrier volume, and spray pressure is herbicide- and weed species-specific.

Limited information exists on the tolerance of sweet maize hybrids to halosulfuron applied post-emergence. The tolerance of eight sweet maize hybrids GG446, GG214, GH2547, GH2041, GH2298, Empire, GH2684, and GSS9299 to halosulfuron applied post-emergence at 25 and 50 g ai ha −1 was evaluated at two Ontario locations in 2005 and 2006. At 7 days after treatment (DAT), Empire and GH2684 hybrids had 4% visible injury at 25 g ai ha −1 , and Empire, GH2684, and GH2298 hybrids had 6–8% visible injury at 50 g ai ha −1 . There was no injury in the other hybrids. At 14 DAT, there was no visible injury at 25 g ai ha −1 in any of the hybrids evaluated but there was 2–6% visual injury at 50 g ai ha −1 in GH2041, GH2298, Empire, GH2684, and GS9299 hybrids. The injury to all hybrids was transient, with no significant injury observed at 28 DAT. Visible injury tended to increase as herbicide dose increased. There were no adverse effects on plant height, cob size, and marketable yield for any hybrids except the yield of Empire, which was reduced 14% at 25 g ai ha −1 and 21% at 50 g ai ha −1 . Based on this study, halosulfuron can be safely applied to GG446, GG214, GH2547, GH2041, GH2298, GH2684, and GSS9299 hybrids, but should not be registered for use on the sweet maize hybrid Empire.

Tolerance of white bean to the pre-emergence application of imazethapyr at the dose of 0, 25, 50, 75, 150 and 300 g ai ha−1 was studied at 11 Ontario, Canada locations over a 3-year period. White bean tolerance to imazethapyr was dependent on dose and environmental conditions. Crop injury generally increased as the dose was increased. Imazethapyr-applied pre-emergence caused up to 62% visible injury and reduced plant height as much as 32%, shoot dry weight 48%, root dry weight 20% and yield 77%. Seed moisture content was increased as much as 1.1%. The dose of imazethapyr to cause 5%, 10% and 20% injury in white bean was as low as 17, 31 and 58 g ai ha−1 for visible injury, 36, 73 and 155 g ai ha−1 for plant height, 4, 9 and 22 g ai ha−1 for shoot dry weight, 27, 54 and 108 g ai ha−1 for root dry weight, and 10, 21 and 44 g ai ha−1 for yield, respectively. Leaf tissue potassium (K) concentration was not affected with imazethapyr at 25, 50 and 75 g ai ha−1; however, it was reduced 27% at 150 g ai ha−1 and 36% at 300 g ai ha−1. Based on these results, imazethapyr-applied pre-emergence at the currently registered dose of 75 g ai ha−1 in white bean in Ontario has the potential to cause significant crop injury and yield losses under some environmental conditions.

In glyphosate-tolerant crops, weed control may be improved and glyphosate dose may be reduced when ammonium sulfate (AMS) is added to the spray mixture. Much research has investigated how AMS may reduce antagonism between salt ions present in the carrier water and glyphosate molecules, especially when hard water is used as the spray carrier. However, little information is available describing whether glyphosate dose may be reduced when soft water is used. Field trials were established at two Ontario and one Michigan location in 2003 and 2004 to evaluate control of several annual weeds when 0.25, 0.5, 0.75 and 1× label doses of glyphosate ±2% AMS were applied in glyphosate-tolerant maize. The concentration of salt and metal ions in the spray water at Harrow and Ridgetown were low, and the concentrations at East Lansing were moderate. Crop tolerance was excellent in all treatment plots. The addition of AMS only improved weed control at the Ridgetown location. Control of Abutilon theophrasti was improved at the 0.25 and 0.5× glyphosate doses; however, improvements in control did not exceed 65%. Percent weed control below 80% is generally considered unacceptable. Control of Amaranthus retroflexus , Chenopodium album , and several annual grasses was not improved by AMS addition at any glyphosate dose in comparison to the application of glyphosate alone. Overall, the addition of AMS to a soft water carrier improved control of some weed species only at below-label glyphosate doses. Nonetheless, because weed control was not improved beyond 70% when AMS was added, we continue to recommend that the full label dose of glyphosate be applied to reduce the necessity for additional glyphosate applications to maintain acceptable weed control.

Four field trials were conducted over a 2 year period at Exeter (2005, 2006), Harrow (2006), and Ridgetown (2006), Ontario, Canada, to evaluate the tolerance of pinto and small red Mexican (SRM) beans to the preplant-incorporated (PPI) application of trifluralin, dimethenamid, S-metolachlor, KIH-485, imazethapyr, and flumetsulam. All the treatments, including the untreated control, were maintained weed-free during the growing season. The PPI application of trifluralin, dimethenamid, and S-metolachlor resulted in minimal transient visual injury, with no adverse effect on the plant height, shoot dry weight, seed moisture content, and yield of the pinto and SRM beans. The PPI application of imazethapyr and flumetsulam, especially at the high rate, initially caused 13% injury and reduced the plant height and shoot dry weight by 15 and 28%, respectively, but these injuries were transient and had no effect on the seed maturity and yield of the pinto and SRM beans. The PPI application of KIH-485 caused 80% injury to the pinto and SRM beans and reduced the plant height, shoot dry weight, and yield. The dry bean maturity was also delayed. Based on these results, trifluralin, dimethenamid, S-metolachlor, imazethapyr, and flumetsulam, applied as PPI herbicides, have the potential to be used in a weed management program for pinto and SRM beans. However, KIH-485, applied as a PPI herbicide at the doses evaluated, does not have an adequate margin of crop safety for use in pinto and SRM bean production in Ontario.

Four field trials were conducted over a two-year period at Exeter (2005, 2006), Harrow (2006) and Ridgetown (2006), Ontario to evaluate the tolerance of pinto and Small Red Mexican (SRM) beans to the pre-emergence application of dimethenamid-p at 693 and 1386 g ai ha −1 , s -metolachlor at 1600 and 3200 g ai ha −1 , pyroxasulfone at 209 and 418 g ai ha −1 , imazethapyr at 75 and 150 g ai ha −1 , linuron at 1125 and 2250 g ai ha −1 , flumetsulam at 70 and 140 g ai ha −1 and cloransulam-methyl at 35 and 70 g ai ha −1 . All treatments including the non-treated control were maintained weed free during the growing season. Dimethenamid-p and s -metolachlor, especially at high doses, caused up to 19% visual injury to pinto and SRM, but these injuries were transient and had no effect on maturity and yield. Pyroxasulfone and linuron caused as much as 33% visual injury and reduced plant height, shoot dry weight and yield by up to 29, 36 and 25%, respectively. Imazethapyr, flumetsulam and cloransulam-methyl caused less than 5% visual injury and had no adverse effect on plant height, shoot dry weight, seed moisture content and yields of pinto and SRM beans. Based on these results dimethenamid-p, s -metolachlor, imazethapyr, flumetsulam and cloransulam-methyl applied pre-emergence have potential for inclusion in a weed management program for pinto and SRM beans. However, pyroxasulfone and linuron, applied pre-emergence at the doses evaluated do not have an adequate margin of crop safety for use in pinto and SRM bean production.

Four field trials were conducted over a 2-yr period at Exeter (2005, 2006), Harrow (2006) and Ridgetown (2006), Ontario to evaluate the tolerance of pinto and small red Mexican (SRM) bean to the POST application of bentazon, imazethapyr, or their combination. Bentazon applied once or twice (to simulate a spray overlap in the field) at 840 g ai/ha and imazethapyr applied at 37.5 g/ha caused minimal injury (6% or less) in pinto and SRM bean and had no adverse effect on plant height, shoot dry weight, seed moisture content, and yield. Imazethapyr applied twice at 37.5 and all single and repeat applications containing 75 or 150 g/ha caused 15 to 44% injury to dry bean. These injuries were persistent and reduced plant height by as much as 21% and shoot dry weight by as much as 34%, but caused no adverse effect on maturity and yield, except for imazethapyr applied twice at 150 g/ha, which delayed maturity and reduced yield 16%. The addition of bentazon to imazethapyr applied as a tankmix reduced injury by as mu...

There is limited information on the effect of s-metolachlor application timing on cabbage tolerance in Ontario. A total of five field trials (1999–2004) were established near Ridgetown Ontario, Canada to evaluate tolerance of cabbage to s-metolachlor applied pretransplant incorporated, pre-transplant and post-transplant at 800, 1600 and 2400 g a.i./ha. s-Metolachlor applied pre-transplant incorporated, pre-transplant and post-transplant at 800, 1600 and 2400 g a.i./ha did not have any effect on visual injury, marketable head production, marketable head weight and yield of cabbage. There was also no difference among s-metolachlor application timings (pretransplant incorporated, pre-transplant and post-transplant) in respect to cabbage tolerance. Based on these results s-metolachlor applied pre-transplant incorporated, pre-transplant and post-transplant at 800, 1600 and 2400 g a.i./ha has an acceptable level of crop safety in cabbage. r 2007 Elsevier Ltd. All rights reserved.

Eight field trials were conducted in Ontario and Michigan over a 2-year period (2005 and 2006) to study the efficacy of five sulfonylurea herbicides for the control of Muhlenbergia frondosa (wirestem muhly) in field maize. Treatments consisted of a non-treated control, a weed-free control, and post-emergence applied rimsulfuron (15 g a.i./ha), nicosulfuron (25 g a.i./ha), nicosulfuron plus rimsulfuron (25 g a.i./ha), foramsulfuron (35 g a.i./ha), and primisulfuron (25 g a.i./ha). All treatments included 141 g a.i./ha of dicamba for broadleaved weed control. Rimsulfuron provided up to 32% control of M. frondosa , had no effect on density and dry weight but increased maize yield 11%. Nicosulfuron provided up to 49% control of M. frondosa and reduced density 44%, dry weight 70%, and increased maize yield 22%. Nicosulfuron plus rimsulfuron controlled M. frondosa up to 43%, had no effect on density, decreased dry weight 46%, and increased maize yield 16%. Foramsulfuron provided up to 89% control of M. frondosa , decreased density 76%, decreased dry weight 94%, and increased maize yield 17%. Primisulfuron provided up to 32% M. frondosa control but had no effect on density, dry weight or maize yield. Based on these results, foramsulfuron post-emergence has potential for the control of M. frondosa in maize. However, rimsulfuron, nicosulfuron, nicosulfuron plus rimsulfuron, and primisulfuron applied post-emergence do not provide adequate control of M. frondosa in maize.

There are few pre-transplant herbicides for weed control in cole crops in Ontario. Three field trials were established each year in 2003, 2004, and 2005 at Ridgetown, Ontario, Canada to evaluate broccoli, cabbage, and cauliflower tolerance to oxyfluorfen (560 and 1120 g a.i./ha), dimethenamid-p (750 and 1500 g a.i./ha), sulfentrazone (100 and 200 g a.i./ha), and a tank-mix of dimethenamid-p plus sulfentrazone (750+100 and 1500+200 g a.i./ha), representing once and twice the proposed use dose for each herbicide/tankmix. Treatments included a non-treated weed-free control. Oxyfluorfen, dimethenamid-p, sulfentrazone, and dimethenamid-p plus sulfentrazone applied pre-transplant at the proposed and twice the proposed use dose in broccoli, cabbage, and cauliflower did not cause any visual injury, and did not reduce number of heads produced, head weight or yield in all nine trials conducted. Based on these results, oxyfluorfen, dimethenamid-p, sulfentrazone, and dimethenamid-p plus sulfentrazone all have an acceptable level of crop safety for use at the proposed dose in broccoli, cabbage, and cauliflower.