Peter H. Sikkema

Sweet Corn (Zea mays) Cultivar Sensitivity to Mesotrione

Field studies were conducted in 1999 and 2000 at Simcoe, Ridgetown, and Exeter, Ontario, to evaluate the tolerance of nine sweet corn cultivars to mesotrione, applied preemergence (PRE) at 140 and 280 g ai/ha and postemergence (POST) at 100 and 200 g ai/ha. Urea ammonium nitrate fertilizer (28%) at 2.5% (v/v) and crop oil concentrate at 1% (v/v) were added to POST applications of mesotrione only. All cultivars were tolerant to mesotrione applied PRE. There was no injury, or reductions in plant height or yield with PRE applications of mesotrione at any location in either year. POST applications of mesotrione, particularly at 200 g/ha, caused significant phytotoxicity to ‘Calico Belle’ and ‘Del Monte 2038’. Other cultivars also showed phytotoxic symptoms; however, this injury was much reduced and did not occur at all locations each year. Sweet corn injury by mesotrione increased as rate increased. Del Monte 2038 also had significantly reduced plant height and yields. Other cultivars had no plant height or yield reductions because of POST applications of mesotrione. Nomenclature: Mesotrione; sweet corn, Zea mays L. Additional index words: Crop injury, plant height, triketone. Abbreviations: DAP, days after planting; DAT, days after treatment; HPPD, p-hydroxy-phenylpyruvate dioxygenase; OM, organic matter; PRE, preemergence; POST, postemergence; SU, sulfonylurea.

Control of Volunteer Glyphosate-Resistant Corn (Zea mays) in Glyphosate-Resistant Soybean (Glycine max)1

Volunteer corn in soybean can reduce yields, interfere with harvest, and cause unacceptable levels of contamination by its presence in the harvested soybean. In Ontario, soybean frequently follow corn in rotation. The use of glyphosate-resistant corn and soybean varieties has increased dramatically in Ontario. Field studies were conducted at two locations in southwestern Ontario to determine whether quizalofop-p-ethyl, clethodim, and fenoxaprop-p-ethyl can be tank mixed with glyphosate to provide effective control of volunteer glyphosate-resistant corn in glyphosate-resistant soybean. Soybean plots were overseeded with glyphosate-resistant corn and treatments consisting of glyphosate applied alone and tank mixed with full and reduced rates of each graminicide with and without a recommended surfactant. Tank mixing the graminicides and adjuvants with glyphosate did not affect glyphosate weed control or crop tolerance. Use of a recommended adjuvant significantly improved the effectiveness of the graminicides, particularly when reduced rates were applied. Quizalofop-p-ethyl was the most effective graminicide for controlling glyphosate-resistant volunteer corn, followed by clethodim and fenoxaprop-p-ethyl. Nomenclature: Soybean, Glycine max (L.) Merr. ‘Pioneer 9294 RR’; volunteer corn, Zea mays L. Additional index words: Graminicides, efficacy. Abbreviation: DAT, days after treatment.

Tolerance of Black Beans (Phaseolus vulgaris) to Soil Applications of S-Metolachlor and Imazethapyr1

This study was conducted to evaluate the tolerance of two black bean cultivars, AC Harblack and Midnight Black Turtle, to preplant incorporated (PPI) and preemergence (PRE) applications of S-metolachlor at 1.6 and 3.2 kg ai/ha, imazethapyr at 0.075 and 0.15 kg ai/ha, and S- metolachlor plus imazethapyr at 1.6 plus 0.075 and 3.2 plus 0.15 kg ai/ha, respectively, at Exeter and Ridgetown, Ontario, Canada, in 2001 and 2002. There were generally no differences between the two cultivars in their responses to the herbicide treatments. PPI and PRE applications of S- metolachlor did not reduce black bean growth or yield. The PPI and PRE applications of imazethapyr alone or in tank mixture with S-metolachlor at the low and high rates did not have a significant effect on plant height, dry weight, seed moisture content, or yield at Ridgetown but caused as much as 14% visual crop injury at Exeter and reduced plant height, dry weight, and yield as much as 25, 40, and 49%, respectively. The higher rate of either herbicide alone or in tank mixture generally caused greater crop injury than the lower rate. At sites where there was a significant difference, the PPI application caused less crop injury than the PRE application. On the basis of these results, the PPI and PRE applications of S-metolachlor can be applied safely at the recommended label rate for the control of annual grass in black beans. However, the PPI and the PRE applications of imazethapyr alone and in tank mixture with S-metolachlor require careful application to avoid spray overlaps because there is potential for crop injury and yield reduction under some environmental conditions. Nomenclature: Imazethapyr; S-metolachlor; black bean, Phaseolus vulgaris L. ‘AC Harblack’, ‘Midnight Black Turtle’. Additional index words: Crop injury, crop tolerance, maturity, plant dry weight, plant height, yield. Abbreviations: DAE, days after emergence; PPI, preplant incorporated; PRE, preemergence.

Tolerance of White Beans to Postemergence Broadleaf Herbicides

Weed control in white beans is currently limited by the small number of registered herbicides. The tolerance of two white bean cultivars, ‘AC Compass’ and ‘OAC Thunder’, to various postemergence (POST) herbicides at the maximum use rate and twice the maximum use rate for soybean or corn was evaluated at two Ontario locations in 2001 and 2002. Generally, the two cultivars did not differ in their response to the POST herbicides. POST applications of imazamox plus fomesafen, imazamox plus bentazon, and cloransulam-methyl decreased plant height, shoot dry weight, and yield by as much as 29, 41, and 55%, respectively, and increased seed moisture content up to 3.9%. POST applications of thifensulfuron, chlorimuron, and bromoxynil decreased plant height as much as 57%, shoot dry weight by up to 71%, yield as much as 93% and increased seed moisture content up to 15.5%. Based on these results, AC Compass and OAC Thunder white beans do not possess sufficient tolerance to support the registration of imazamox plus bentazon, imazamox plus fomesafen, cloransulam-methyl, thifensulfuron, chlorimuron, and bromoxynil. Nomenclature: Bentazon; bromoxynil; chlorimuron; cloransulam-methyl; fomesafen; imazamox; thifensulfuron; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; white bean, Phaseolus vulgaris L. ‘AC Compass’, ‘OAC Thunder’. Additional index words: Crop tolerance, herbicide injury, postemergence herbicides, seed moisture content, white beans, yield. Abbreviations: DAP, days after planting; DAT, days after treatment; POST, postemergence.

Weed control in glufosinate-resistant corn (Zea mays).

Abstract: The development of glufosinate-resistant corn represents a new weed management system for corn growers. Field experiments were conducted from 1995 to 1997 at four locations in southwestern Ontario. The objective of this study was to determine the effect of timing of weed control relative to the growth stage of corn with glufosinate applied alone or in combination with residual herbicides. Control of all species tested improved with the addition of atrazine plus dicamba to glufosinate, applied from the two- to eight-leaf stage of corn growth. Based on a 90% weed dry matter reduction, glufosinate with atrazine plus dicamba controlled common ragweed, common lambsquarters, and pigweed species at the three-leaf stage of corn and yellow foxtail, barnyardgrass, and large crabgrass at the two-, four-, and eight-leaf stage of corn, respectively. Weed control with glufosinate alone was improved when applied at the later growth stages of corn. Glufosinate applied alone at the four-leaf stage of corn controlled common ragweed and common lambsquarters, whereas pigweed species were controlled effectively at the eight-leaf stage of corn growth. Corn grain yield was consistently higher when glufosinate was applied in combination with residual herbicides, compared to glufosinate alone. Glufosinate in combination with residual herbicides applied to corn at the three- to five-leaf stage may represent the best timing for weed control. Our data suggested that a tank mixture of glufosinate with other postemergence residual herbicides or a split application of glufosinate in combination with cultivation may be required for weed control in glufosinate-resistant corn. Nomenclature: Atrazine; dicamba; SAN 582 (proposed name, dimethenamid), 2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)-acetamide; glufosinate; metolachlor; redroot pigweed, Amaranthus retroflexus L. #3 AMARE; common lambsquarters, Chenopodium album L. # CHEAL; yellow foxtail, Setaria glauca (L.) Beauv. # SETGL; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCR; common ragweed, Ambrosia artemisiifolia L. # AMBEL; corn, Zea mays L. Additional index words: Integrated weed management. Abbreviations: DAE, days after emergence; DM, dry matter; HRC, herbicide-resistant crops; IWM, integrated weed management; POST, postemergence; PRE, preemergence.

Glyphosate-Resistant Giant Ragweed (Ambrosia trifida) Control in Dicamba-Tolerant Soybean

Abstract Glyphosate-resistant (GR) giant ragweed has been confirmed in Ontario, Canada. Giant ragweed is an extremely competitive weed and lack of control in soybean will lead to significant yield losses. Seed companies have developed new herbicide-resistant (HR) crop cultivars and hybrids that stack multiple HR traits. The objective of this research was to evaluate the efficacy of glyphosate and glyphosate plus dicamba tank mixes for the control of GR giant ragweed under Ontario environmental conditions in dicamba-tolerant (DT) soybean. Three field trials were established over a 2-yr period (2010 and 2011) on farms near Windsor and Belle River, ON. Treatments included glyphosate (900 g ae ha−1), dicamba (300 g ae ha−1), and dicamba (600 g ha−1) applied preplant (PP), POST, or sequentially in various combinations. Glyphosate applied PP, POST, or sequentially provided 22 to 68%, 40 to 47%, and 59 to 95% control of GR giant ragweed and reduced shoot dry weight 26 to 80%, 16 to 50%, and 72 to 98%, respectively. Glyphosate plus dicamba applied PP followed by glyphosate plus dicamba applied POST consistently provided 100% control of GR giant ragweed. DT soybean yield correlated with GR giant ragweed control. This is the first report in Canada of weed control in DT soybean, specifically for the control of GR giant ragweed. Results indicate that the use of dicamba in DT soybean will provide an effective option for the control of GR giant ragweed in Ontario. Nomenclature: dicamba; glyphosate; giant ragweed, Ambrosia trifida L.; soybean, Glycine max (L.) Merr.

Sensitivity of Leguminous Crops to Saflufenacil

Abstract There is little information on the tolerance of leguminous crops to saflufenacil. A field study was conducted three times over a 2-yr period (2006, 2007) in Ontario, Canada, to determine the tolerance of adzuki bean, cranberry bean, lima bean, processing pea, snap bean, soybean, and white (navy) bean to saflufenacil applied PRE at 100 and 200 g ai/ha. Saflufenacil caused 51 to 99% injury, reduced height 25 to 93%, reduced shoot dry weight 92 to 99%, and reduced seed yield 56 to 99% in adzuki bean, cranberry bean, lima bean, snap bean, and white bean. Injury was lower in soybean and processing pea. Saflufenacil caused 1 to 25% injury, reduced height 3 to 13%, reduced shoot dry weight 5 to 30%, and reduced seed yield 0 to 4% in soybean and processing pea. Cranberry bean, snap bean, white bean, and lima bean were the most sensitive crops to saflufenacil followed by adzuki bean. Soybean and processing pea were the most tolerant to saflufenacil. Based on these results, saflufenacil applied PRE can be safely used in specific cultivars of pea and soybean at the proposed rate of 100 g/ha. However, there is not an acceptable margin of crop safety for saflufenacil PRE at 100 or 200 g/ha in adzuki, cranberry, lima, snap, and white bean. Abstract Existe muy poca información sobre la tolerancia del cultivo de leguminosas hacia el saflufenacil. Un estudio de campo fue llevado al cabo tres veces durante un período de 2 años (2006, 2007) en Ontario para determinar la tolerancia del Vigna angularis L. ‘Erimo’, Phaseolus vulgaris L. ‘Etna’, Phaseolus lunatus L. ‘Kingston’, Lathyrus odoratus L. ‘Durango’, Phaseolus vulgaris L. ‘Matador’, Glycine max L. ‘DK 28-52R’, y Phaseolus vulgaris L. ‘OAC Rex’ al saflufenacil aplicado en pre-siembra a 100 y 200 g ia/ha. El saflufenacil causó de un 51 a un 99% de daño, redujo la altura de las plantas en un 25 a un 93%, disminuyó el peso seco de la parte aérea de un 92 a un 99%, así como también redujo la producción de semilla de un 56 a un 99% en Vigna angularis, Phaseolus vulgaris Etna, Phaseolus lunatus, Phaseolus vulgaris Matador, y Phaseolus vulgaris OAC Rex. El daño fue menor en Glycine max y en Lathyrus odoratus. El saflufenacil ocasionó del 1 al 25% de daño, redujo la altura de un 3% a un 13%, el peso seco de la parte aérea disminuyó de un 5 a un 30% y bajó el rendimiento de semilla de 0 a 4% en la soya y el chícharo. Phaseolus vulgaris Etna, Phaseolus vulgaris Matador, Phaseolus vulgaris OAC Rex, y Phaseolus lunatus fueron los cultivos más sensibles al saflufenacil seguidos por Vigna angularis. Glycine max y Lathyrus odoratus fueron los más resistentes al herbicida. Basándose en estos resultados, el saflufenacil aplicado en pre-siembra puede ser usado con seguridad en los cultivares específicos de Lathyrus odoratus y Glycine max a la dosis propuesta de 100 g ia /ha. Sin embargo, no existe margen aceptable de seguridad para el saflufenacil aplicado en pre-siembra a 100 o 200 g ia/ha en el cultivo de Vigna angularis, Phaseolus vulgaris Etna, Phaseolus lunatus, Phaseolus vulgaris Matador, y Phaseolus vulgaris OAC Rex. Nomenclature: Saflufenacil, adzuki bean, Vigna angularis L. ‘Erimo’, cranberry bean, Phaseolus vulgaris L. ‘Etna’, lima bean, Phaseolus lunatus L. ‘Kingston’, pea, Lathyrus odoratus L. ‘Durango’, snap bean Phaseolus vulgaris L. ‘Matador’, soybean, Glycine max L. ‘DK 28-52R’, white bean, Phaseolus vulgaris L. ‘OAC Rex’

White Bean Sensitivity to Preemergence Herbicides

White bean producers have a limited number of herbicide options available for annual grass and broadleaf weed control. Tolerance of two white bean cultivars to preemergence (PRE) applications of S-metolachlor, S-metolachlor + imazethapyr, flumetsulam + S-metolachlor, cloransulam-methyl, clomazone, clomazone + imazethapyr, and clomazone + S-metolachlor at the maximum labeled rate in soybean (1×) and twice the labeled rate (2×) were studied at two Ontario locations (Exeter and Ridgetown) in 2001 and 2002. S-Metolachlor, clomazone, and clomazone + S-metolachlor generally had no negative effect on plant height, dry weight, maturity, and yield. S-Metolachlor + imazethapyr and clomazone + imazethapyr reduced plant height, dry weight, and yield as much as 21, 42, and 24%, respectively. Flumesulam + S-metolachlor and cloransulam-methyl reduced plant height, dry weight, and yield as much as 39, 58, and 43%, respectively. White beans are tolerant to PRE applications of S-metolachlor, clomazone, and clomazone + S-metolachlor. White beans are sensitive to PRE applications of S-metolachlor + imazethapyr, flumetsulam + S-metolachlor, clomazone + imazethapyr, and cloransulam-methyl. Nomenclature: Clomazone; cloransulam-methyl; flumetsulam; imazethapyr; S-metolachlor; soybean, Glycine max (L.) Merr; white bean, Phaseolus vulgaris L. Additional index words: Dry beans, herbicide tolerance, preemergence herbicides, white beans. Abbreviations: DAE, days after emergence; PRE, preemergence; 1× rate, the maximum recommended herbicide labeled rate in soybean; 2× rate, twice the maximum recommended herbicide labeled rate in soybeans.

Response of Corn to Preemergence and Postemergence Applications of Saflufenacil

Abstract 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. Nomenclature: BAS 800H; saflufenacil; corn, Zea mays L.

Environmental Impact of Glyphosate-Resistant Weeds in Canada

Abstract Glyphosate-resistant (GR) giant ragweed, horseweed, and common ragweed were confirmed in southwestern Ontario, Canada in 2008, 2010, and 2011, respectively. In the western prairie provinces of Alberta and Saskatchewan, GR (plus acetolactate synthase inhibitor-resistant) kochia was discovered in 2011. This symposium paper estimates the environmental impact (EI) of the top herbicide treatments or programs used to manage these GR weed species in the major field crops grown in each region. For each herbicide treatment, EI (per ha basis) was calculated as the environmental impact quotient (EIQ), which quantifies the relative potential risk of pesticide active ingredients on human and ecological health based on risk components to farm workers, consumers, and the environment, multiplied by the application rate (kg ai ha−1). Total EI is defined as EI (per ha basis) multiplied by the application area (i.e., land area affected by a GR weed). It was assumed that all herbicide treatments would supplement the continued usage of glyphosate because of its broad spectrum weed control. For the control of these GR weeds, most treatments contain auxinic or protoporphyrinogen oxidase (PPO)-inhibiting herbicides. The majority of auxinic herbicide treatments result in low (EI ≤ 10) to moderate (11 to 20) EI, whereas all treatments of PPO inhibitors have low EI. Total EI of GR horseweed and kochia will generally be greater than that of giant or common ragweed because of rapid seed dispersal. For recommended herbicide treatments to control GR weeds (and herbicide-resistant weeds in general), EI data should be routinely included with cost and site of action in weed control extension publications and software, so that growers have the information needed to assess the EI of their actions. Nomenclature: Glyphosate; common ragweed, Ambrosia artemisiifolia L. AMBEL; giant ragweed, Ambrosia trifida L. AMBTR; horseweed, Conzya canadensis (L.) Cronq. ERICA; kochia, Kochia scoparia (L.) Schrad. KCHSC, synonym: Bassia scoparia (L.) A.J. Scott.