Darren E. Robinson

Barley seeding rate influences the effects of variable herbicide rates on wild oat

Abstract Field experiments were conducted at Vegreville, Alberta, in 1997, 1998, and 1999 and in Lacombe, Alberta, in 1997 and 1998, to determine if barley row spacing (20 and 30 cm) and seeding rate (75, 125, and 175 kg ha−1) influenced the effects of variable tralkoxydim rates on barley seed yield, net economic returns, and wild oat seed production. In most cases, barley seed yield was unaffected by row spacing or seeding rate. Where no herbicide was applied, the presence of wild oat reduced barley yield at each location each year. When the herbicide was applied at 50, 75, or 100% of the recommended rate, barley yields were not affected by the presence of wild oat. Results were more variable at 25% of the recommended rate, especially at Lacombe, where yield losses occurred both years at this rate. The lowest net economic returns consistently occurred in the absence of herbicide application; however, the influence of herbicide rate on net returns varied among years and locations. Net returns were either higher at the lower herbicide rates or were unaffected by herbicide rate. Seeding rate and herbicide rate affected wild oat seed production at each location each year and also the amount of seeds in the soil seedbank at Vegreville in 1999. Row spacing had little or no effect on wild oat seed production. There was a consistent and highly significant seeding rate by herbicide rate interaction on wild oat seed production. The effects of tralkoxydim on wild oat seed production, especially at relatively low rates, were superior at the higher barley seeding rates. The results suggest that seeding barley at relatively high rates can result in optimum barley yields, undiminished economic returns, and effective wild oat management when tralkoxydim is used at lower than recommended rates. Nomenclature: Bromoxynil; glyphosate; MCPA; tralkoxydim; barley, ‘Falcon’, Hordeum vulgare L.; wild oat, Avena fatua L. AVEFA.

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.

The Critical Weed-Free Period in Carrot

Abstract Seeding date and the duration of weed emergence influenced the duration of the critical weed-free period in carrot. The critical weed-free period extended up to 930 growing degree days (GDD), when carrot was seeded in late April. In contrast, the critical weed-free period was short and lasted 414 to 444 GDD, when seeded in mid to late May and weed biomass was less than 650 g m−2. It is important for growers to scout fields for weeds until 930 GDD to protect the yield potential of the carrot crop in earlier planted crops; however, for carrot planted in mid to late May, weeds emerging after 444 GDD did not reduce yield. A useful strategy to reduce reliance on herbicide application would be to delay planting until late in May. Nomenclature: Carrot, Daucus carota L.

Atrazine Accentuates Carryover Injury from Mesotrione in Vegetable Crops

Abstract Trials were established in 2003, 2004, and 2005 in Ontario to determine the effects of residues of mesotrione, atrazine, and mesotrione plus atrazine 1 and 2 yr after application on broccoli, carrot, cucumber, onion, and potato. One yr after mesotrione application, injury was 43, 37, 18, 24, and 0% in broccoli, carrot, cucumber, onion, and potato, respectively. The addition of atrazine to mesotrione in the year before planting increased injury to 55, 53, 30, 42, and 3% in broccoli, carrot, cucumber, onion, and potato, respectively. Plant dry weight and yield were also decreased by mesotrione residues the year after application in all crops except potato. The addition of atrazine to mesotrione accentuated the reduction in dry weight and yield in broccoli, carrot, cucumber, and onion. There was no injury, or reductions in dry weight or yield in any crop planted 2 yr after application of mesotrione alone or in tank mix with atrazine. A recropping interval of 2 yr is recommended following applications of mesotrione or mesotrione plus atrazine for broccoli, carrot, cucumber, and onion. Potato can be safely planted the year following application of mesotrione plus atrazine. Nomenclature: Atrazine; mesotrione; broccoli, Brassica oleracea var. italica Plenck.; carrot, Daucus carota L.; cucumber, Cucumis sativus L.; onion, Allium cepa L.; potato, Solanum tuberosum L;

Weed Populations, Sweet Corn Yield, and Economics Following Fall Cover Crops

Abstract The effectiveness of cover crops as an alternative weed control strategy should be assessed as the demand for food and fiber grown under sustainable agricultural practices increases. This study assessed the effect of fall cover crops on weed populations in the fall and spring prior to sweet corn planting and during sweet corn growth. The experiment was a split-plot design in a pea cover–cover crop–sweet corn rotation with fall cover crop type as the main plot factor and presence or absence of weeds in the sweet corn as the split-plot factor. The cover crop treatments were a control with no cover crop (no-cover), oat, cereal rye (rye), oilseed radish (OSR), and oilseed radish with rye (OSR+rye). In the fall, at Ridgetown, weed biomass in the OSR treatments was 29 and 59 g m−2 lower than in the no-cover and the cereal treatments, respectively. In the spring, OSR+rye and rye reduced weed biomass, density, and richness below the levels observed in the control at Bothwell. At Ridgetown in the spring, cover crops had no effect on weed populations. During the sweet corn season, weed populations and sweet corn yields were generally unaffected by the cover crops, provided OSR did not set viable seed. All cover crop treatments were as profitable as or more profitable than the no-cover treatment. At Bothwell profit margins were highest for oat at almost Can

Occurrence and distribution of glyphosate-resistant giant ragweed (Ambrosia trifida L.) in southwestern Ontario

600 ha−1 higher than the no-cover treatment. At Ridgetown, compared with the no-cover treatment, OSR and OSR+rye profit margins were between Can

Control of Glyphosate-Resistant Horseweed (Conyza canadensis) with Dicamba Applied Preplant and Postemergence in Dicamba-Resistant Soybean

1,250 and Can

Response of Pinto and Small Red Mexican Bean to Postemergence Herbicides

1,350 ha−1 and between Can

Effect of Perennial Ryegrass Overseeding on Weed Suppression and Sward Composition

682 and Can

Sweet Corn (Zea mays) Cultivar Sensitivity to AE F1303601

835 ha−1, respectively. Therefore, provided that OSR does not set viable seed, the cover crops tested are feasible and profitable options to include in sweet corn production and provide weed-suppression benefits. Nomenclature: Cereal rye, Secale cereale L.; oat, Avena sativa L.; oilseed radish, Raphanus sativus L. var. oleoferus Metzg. Stokes; pea, Pisum sativum L.; sweet corn, Zea mays L.