Christy Shropshire

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.

Sensitivity of kidney beans (Phaseolus vulgaris) to soil applications of S-metolachlor and imazethapyr

Tolerance of Montcalm and Redhawk kidney beans to preplant incorporated (PPI) and preemergence (PRE) applications of S-metolachlor, imazethapyr and their tank mix at the maximum label rate in soybeans (1×) and twice that rate (2×) was studied at two Ontario locations (Exeter and Ridgetown) in 2001 and 2002. There were no differences between the two cultivars in their responses to the herbicide treatments. Visual evaluations of crop injury never exceeded 2% for any herbicide treatment. With the exception of a 7% height reduction after the PPI application of imazethapyr plus S-metholachlor at the 2× rate, none of the other treatments reduced plant height, dry weight, seed moisture content or seed yield. At sites where there was a significant difference, the PRE application caused more crop injury than the PPI application. These results indicate that there is an acceptable margin of crop safety for PPI and PRE applications of S-metolachlor and imazethapyr alone and in tank mix combination in kidney beans in ...

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.

Response of common lambsquarters (Chenopodium album) to glyphosate application timing and rate in glyphosate-resistant corn

Field studies were conducted over 3 yr at two locations to evaluate the effect of glyphosate rate and time of application on common lambsquarters control, density, dry weight, seed production, and the number of seedlings emerging from soil cores taken the year after herbicide application in glyphosate-resistant corn. Glyphosate was applied at 0, 112, 225, 450, 675, or 900 g ai/ha when common lambsquarters were at the two-, four-, or six-leaf stage of growth. Nicosulfuron was applied to all experimental areas to control annual grasses. Visual estimates of percent control increased, whereas density, dry weight, seed production, and seedlings emerging the year after treatment decreased as the rate of glyphosate was increased from 0 to 450 g/ha. Increasing the glyphosate rate above 450 g/ha had little effect on these parameters. Corn yield declined only at glyphosate rates below 450 g/ha. Time of application had no effect on common lambsquarters control and corn yield because little emergence occurred after the first glyphosate application. There was no interaction between glyphosate rate and time of application for any of the parameters evaluated. In these studies, the application of glyphosate at half the manufacturers registered rate provided control of common lambsquarters equivalent to the full-registered rate with no measured increase in weed seed production and no increase in weed seedlings emerging from soil cores the year after herbicide application. The results suggest that in some cases the use of reduced herbicide rates can provide excellent weed control and maintain crop yields, while reducing the cost of production and the environmental impact of herbicides. The use of extremely low rates (112 or 225 g/ha), however, resulted in reduced corn yields, increased common lambsquarters seed production and seedlings emerging the year after application, and possibly increased weed management costs in subsequent years. Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. #3 CHEAL; corn, Zea mays L. ‘Pride G4286’, ‘DeKalb 493RR’. Additional index words: Reduced rates, weed control, weed seed production. Abbreviation: DAA, days after application.

Giant ragweed (Ambrosia trifida L.) control in corn

Soltani, N., Shropshire, C. and Sikkema, P. H. 2011. Giant ragweed (Ambrosia trifidaL.) control in corn. Can. J. Plant Sci. 91: 577-581. Twelve field trials (five with PRE and seven with POST herbicides) were conducted over a 4-yr period (2006-2009) on various Ontario farms with heavy giant ragweed infestations (22 plants m-2) to determine the effectiveness of preemergence (PRE) and postemergence (POST) herbicides for the control of giant ragweed in corn. Atrazine, dicamba, dicamba/atrazine, isoxaflutole plus atrazine, mesotrione plus atrazine, saflufenacil, and saflufenacil/dimethenamid applied PRE provided 9-52, 60-80, 64-83, 44-77, 33-80, 36-80, and 43-63% control of giant ragweed, reduced giant ragweed density 55, 45, 59, 64, 68, 73, and 77% and reduced giant ragweed shoot dry weight 60, 89, 90, 87, 83, 81, and 78%, respectively. Atrazine, dicamba, dicamba/diflufenzopyr, dicamba/atrazine, 2,4-D/atrazine, bromoxynil plus atrazine, prosulfuron plus dicamba, primisulfuron/dicamba, mesotrione plus atrazine, topramezone plus atrazine, and bentazon/atrazine applied POST provided 46-94, 70-90, 69-84, 82-94, 56-83, 59-76, 66-84, 71-81, 49-81, 34-78, and 26-84% control of giant ragweed, reduced giant ragweed density by 65, 82, 71, 82, 76, 76, 59, 65, 59, 47, and 71% and reduced giant ragweed shoot dry weight by 97, 99, 97, 99.6, 98, 98, 95, 97, 95, 88, and 96%, respectively. Based on these results, dicamba/atrazine provided the best and most consistent control of giant ragweed in corn of the PRE and POST herbicides evaluated.

Dry Bean Response to Preemergence-Applied Kih-485

Three field trials were conducted over a 2-yr period (2004 and 2005) at Exeter and Ridgetown, Ontario to evaluate the tolerance of eight market classes of dry beans to KIH-485 applied PRE at 210 and 420 g ai/ha. KIH-485 PRE caused as much as 67% visual injury in small-seeded and 44% visual injury in large-seeded dry beans. KIH-485 applied PRE at 420 g/ha reduced plant height up to 47% at Ridgetown and 8% at Exeter in 2004, and reduced height of brown and white bean by 15 and 19%, respectively, but had no effect on the height of the other beans in 2005. Shoot dry weight was not affected at Exeter in 2004 but was reduced by 46% at Ridgetown in 2004 and 14% at Exeter in 2005. In 2004, seed moisture content increased by 5, 6, and 12% in black, otebo, and pinto beans, respectively. Seed yield was reduced up to 27% at Ridgetown and 11% at Exeter in 2004 but was not affected at Exeter in 2005. On the basis of this research, KIH-485 PRE causes unacceptable injury in some dry bean market classes. Nomenclature: KIH-485, dry bean, Phaseolus vulgaris L. black ‘AC Harblack’, brown ‘Berna’, cranberry ‘Hooter’, kidney ‘Montcalm’, otebo ‘Hime’, pinto ‘GTS 900’, white ‘OAC Thunder’, yellow eye ‘GTS 1701’