Saflufenacil/dimethenamid-P is a relatively new prepackaged herbicide mixture that has the potential to provide enhanced weed control in soybean when tank-mixed with reduced doses of imazethapyr. Six field experiments were conducted over a 3-yr period (2011, 2012, and 2013) near Ridgetown and Exeter, Ontario, Canada, to determine the dose of imazethapyr, applied PRE, that must be added to saflufenacil/dimethenamid-P (245 g ai ha−1) to provide effective weed control in soybean. The predicted dose of imazethapyr PRE for 80% control of common lambsquarters, common ragweed, green foxtail, and velvetleaf 8 wk after soybean emergence (WAE) was 66, 180, 137, and 48 g ai ha−1, respectively. In contrast, when tank-mixed with saflufenacil/dimethenamid-P (245 g ha−1), the dose of imazethapyr PRE needed for 80% control of common lambsquarters, common ragweed, green foxtail, and velvetleaf was reduced to 11, 80, 48, and 18 g ha−1, respectively. The control of common lambsquarters, common ragweed, green foxtail, and velvetleaf was improved by 21, 23, 34, and 27%, respectively when saflufenacil/dimethenamid-P (245 g ha−1) was added to imazethapyr PRE. Imazethapyr at 104 g ha−1resulted in soybean yield that was 95% of the weed-free control; however, when tank-mixed with saflufenacil/dimethenamid-P (245 g ha−1) only 54 g ha−1of imazethapyr was required for the same yield level. Based on this study, PRE application of saflufenacil/dimethenamid-P with reduced doses of imazethapyr has the potential to improve soybean yield and provide acceptable weed control (≥ 80%); however, the extent that imazethapyr dose can be reduced is dependent upon weed community composition.

Camelina sativa (L.) Crantz is a biofuel crop with application on the Great Western Plains of North America that is being developed using genetic engineering. Before release of genetically engineered cultivars, the potential for pollen‐mediated gene flow (PMGF) needs to be assessed to determine if they can coexist with conventional cultivars without causing market harm. Medium‐scale field experiments (40‐m diameter) were conducted in 2011 and 2012 to quantify PMGF using a seed‐expressed florescent marker and bar gene that confers resistance to glufosinate [2‐amino‐4‐(hydroxymethylphosphinyl) butanoic acid] in Alberta, Canada. More than 17 million seeds were screened to quantify outcrossing. Pollen‐mediated gene flow best fit an exponential decay model in which the highest average PMGF (0.78%) occurred adjacent to the donor crop and rapidly declined to 0.09% by 20 m. Pollen‐mediated gene flow was leptokurtic, with a 50% reduction in gene flow 1.5 m from the pollen source. No directional trends were detected, suggesting wind dispersal was not influencing experimental results. The risk of PMGF at longer distances is minimal, but not zero, in this primarily self‐pollinating species.

Camelina [Camelina sativa (L.) Crantz.] is an oilseed currently being developed for production of industrial bioproducts. To determine whether camelina is persistent or weedy in agricultural areas experiments were conducted in 2008 through 2011. A three‐part study quantified camelina seed loss at the time of harvest, persistence of seed in the soil, and density and persistence of volunteer populations in subsequent crops. In this small‐seeded crop, seed losses at harvest ranged from 1202 to 43,430 viable seeds m−2 (12.0 to 434.3 kg ha−1). Viable seed persisted less than 15 mo at all depths, sites, and years. Seeds persisted longer on the soil surface while seed buried at 3 and 10 cm depleted more rapidly. The days to 50% seed extinction (EX50) ranged from 25 d for all burial depths at one site in 2009 to 66 d for surface seeds in 2008. Eleven commercial fields planted to camelina in 2009 were surveyed for the presence and persistence of volunteer populations throughout the 2010 and 2011 growing seasons. Initial surveys showed variable densities (9 to 4839 plants m−2); however, populations sharply declined over time and were nearly extinct after 2 yr under conventional production practices. While camelina has high fecundity and large seed losses at harvest, it has limited seed bank persistence and is unlikely to become a weed of agricultural areas.

Glyphosate-resistant (GR) giant ragweed (Ambrosia trifida L.) was first identified in Canada in 2008 and has since been found throughout southwestern Ontario. Six field trials were conducted over a two-year period (2012, 2013) on Ontario farms with GR giant ragweed to evaluate the efficacy of linuron applied pre-plant (PP) in soybean (Glycine max (L.) Merr.). The dose required for 50%, 80%, and 95% GR giant ragweed control was 1238, 2959, and 6018 g·ai·ha −1 four weeks after application (WAA), respectively. The linuron dose needed for 50%, 80%, and 95% reduction in density was 1554, 3181, and 5643 g·ai·ha −1 and 1204, 2496, and 4452 g·ai·ha −1 for dry weight, respectively. Application of 7874 g·ai·ha −1 linuron was needed to obtain soybean yields that were 90% of the weed-free control; approximately 3.5 times the maximum field recommended dose. To achieve 95% and 98% yields, greater than 8640 g·ai·ha −1 linuron was required. Application of linuron plus glyphosate PP in soybean will help to control GR giant ragweed as well as reduce GR selection pressure.

No abstract