Lynette R. Brown

Response of Corn to Simulated Glyphosate Drift Followed by In-Crop Herbicides

Abstract 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

Tolerance of identity preserved soybean cultivars to preemergence herbicides

Belfry, K. D., Soltani, N., Brown, L. R. and Sikkema, P. H. 2015. Tolerance of identity preserved soybean cultivars to preemergence herbicides. Can. J. Plant Sci. 95: 719-726. Six field trials were conducted over a 3-yr period (2011 to 2013) near Exeter and Ridgetown, Ontario, Canada, to assess the tolerance of seven identity-preserved (IP) soybean cultivars to preemergence (PRE) herbicides applied at 2×the recommended dose. All cultivars demonstrated excellent tolerance to dimethenamid-P, pyroxasulfone, S-metolachlor, chlorimuron-ethyl, clomazone, cloransulam-methyl, flumetsulam and imazethapyr, showing 5% or less injury. At Exeter, linuron caused as much as 13 and 18% injury at 2 and 4 wk after soybean emergence, while injury due to metribuzin was as high as 22 and 47% for the same dates, respectively. At Exeter, linuron, metribuzin and S-metolachlor plus metribuzin reduced soybean height up to 17, 41 and 24%, respectively; soybean height was generally not affected at the Ridgetown sites. At Exeter, metribuzin reduced soybean yield up to 38% for cultivars S03W4, Madison and OAC Lakeview, while S23T5 was not significantly reduced. On the contrary, metribuzin yield loss at Ridgetown was nonsignificant. Results from this study suggest that PRE application of metribuzin at 2× field dose has potential to cause unacceptable injury and yield reduction in IP soybeans under some soil and climatic conditions and may vary according to cultivar.

Weed Management in Spring Seeded Barley, Oats, and Wheat with Prosulfuron

A limited number of preplant (PP) herbicides are available for spring seeded cereals in Ontario. Six field trials were conducted at the Huron Research Station, Exeter, Ontario, over a two-year period (Exeter, 2010 and 2011) to evaluate glyphosate, prosulfuron, and glyphosate plus prosulfuron applied PP for weed management in spring seeded no-till barley, oats, and wheat. There was no injury in barley, oats, and wheat with glyphosate, prosulfuron, and glyphosate plus prosulfuron applied preplant at the rates evaluated at 1, 2, and 4 weeks after crop emergence. Prosulfuron provided 49–99% control of AMBEL, 28% or less control of CONAR, 31–94% control of POLCO, 49–98% control of SINAR, and 46–79% control of SONAR. Prosulfuron in combination with glyphosate provided 73–98% control of AMBEL, less than 43% control of CONAR, 39–94% control of POLCO, 63–98% control of SINAR, and 60–85% control of SONAR. Prosulfuron reduced density of AMBEL 76% and SINAR 93% but had no significant effect on density of CONAR, POLCO, or SONAR. Prosulfuron in combination with glyphosate reduced biomass of AMBEL as much as 96% and SINAR 98% but had no significant effect on biomass of CONAR, POLCO, or SONAR. Yield of barley, oats, and wheat was not affected with glyphosate, prosulfuron, and glyphosate plus prosulfuron at the rates evaluated.

Long-spine sandbur [Cenchrus longispinus (Hack. in Kneuck.) Fernald] control in corn

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), nico...

Control of glyphosate-resistant Canada fleabane in soybean with preplant herbicides

Abstract: Thirteen herbicide tankmixes were evaluated during 2013–2015 for control of glyphosate-resistant (GR) Canada fleabane in soybean. Glyphosate + saflufenacil + s-metolachlor/metribuzin, glyphosate + amitrole, and glyphosate + metribuzin were the most efficacious, controlling 86%–92% of GR Canada fleabane, reducing density by 98%–99% and aboveground biomass by 96%–97%.

Simulated mesotrione drift followed by glyphosate, imazethapyr, bentazon or glyphosate plus chlorimuron in soybean.

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 a...

Control of glyphosate-resistant common ragweed in corn with preemergence herbicides

Abstract: Four field experiments were conducted during 2016 and 2017 to evaluate the efficacy of preemergence herbicides to control glyphosate-resistant common ragweed in corn. Dicamba, dicamba/atrazine, mesotrione + atrazine, isoxaflutole + atrazine, saflufenacil/dimethenamid-P, and S-metolachlor/mesotrione/bicyclopyrone/atrazine were the most efficacious herbicides, providing 94%–100% control of GR common ragweed and reducing density and biomass 98%–100%.

Weed control with postemergence glyphosate tank mixes in glyphosate-resistant soybean

Walsh, K. D., Soltani, N., Brown, L. R. and Sikkema, P. H. 2014. Weed control with postemergence glyphosate tank mixes in glyphosate-resistant soybean. Can. J. Plant Sci. 94: 1239-1244. Six field trials were conducted over a 3-yr period (2011, 2012 and 2013) in Ontario, Canada, to evaluate various postemergence (POST) glyphosate tank mixes for weed management in glyphosate-resistant (GR) soybean. Herbicide treatments included glyphosate applied alone or mixed with acifluorfen, fomesafen, bentazon and thifensulfuron-methyl. Glyphosate tank mixtures with acifluorfen, fomesafen, bentazon and thifensulfuron-methyl caused GR soybean injury of up to 21, 11, 4 and 14% at 7 d after treatment (DAT), which was reduced to 5, 0, 0 and 2% by 28 DAT, respectively. Velvetleaf, green pigweed, common ragweed and common lambsquarters control ranged from 55 to 95, 93 to 100, 70 to 92 and 81 to 98% at 28 DAT respectively. Relative to glyphosate alone, tank mixtures with thifensulfuron-methyl provided equivalent to increased weed control, while acifluorfen, fomesafen and bentazon provided equivalent to reduced weed control. All herbicide tank mixtures resulted in higher yields (3.8-4.0 t ha-1) than the untreated check (2.7 t ha-1), and were generally equivalent to glyphosate alone (4.1 t ha-1). Results from this study indicate that the glyphosate tank mixtures evaluated did not provide a benefit over glyphosate alone.