Fusarium root rot complex is a major soybean disease in Canada and the United States. Since 2006, four Fusarium species, F. oxysporum Schlechtendahl emend. Snyder & Hansen, F. graminearum Schwabe, F. avenaceum (Corda: Fr.) Sacc., and F. tricinctum (Corda) Sacc., have frequently been isolated from soybean roots in eastern Ontario, Canada. The objective of the current study was to screen 57 soybean cultivars that are commercially available in Canada for resistance to these four Fusarium root rot pathogens under greenhouse conditions. Based on root rot severity and reductions in seedling emergence, plant height and root dry weight, F. avenaceum was the most pathogenic species, followed by F. graminearum. The pathogenicity of F. oxysporum on soybean cultivars was not significantly different from that of F. tricinctum, but was significantly lower than that of F. graminearum. In replicated experiments, six, nine, eleven and seven cultivars were consistently rated as the most resistant to F. avenaceum, F. graminearum, F. oxysporum and F. tricinctum, respectively. Cultivar Maple Amber was resistant to all four Fusarium species based on root rot severity, while cultivar Altona was resistant to F. avenaceum, F. oxysporum and F. tricinctum. Four cultivars, 9004, AC Harmony, Lanark and Maple Arrow, each showed resistance to two different Fusarium species.Key words: Soybean, Glycine max, Fusarium root rot, Fusarium oxysporum, F. graminearum, F. avenaceum, F. tricinctum

Herbicide dose optimisation, i.e. maximising weed control and crop yield with herbicide dose, is an important part of integrated weed management strategies. However, the adoption of optimised dose technology and variable rate application has been limited because of the relatively long period between herbicide treatment and the time when efficacy can be visually assessed. Herbicide dose optimisation could therefore benefit from simple methods that allow early prediction of plant mortality. Early prediction would allow better management decisions, e.g. timely retreatment in case of uncontrolled weeds. The focus of this study was the relationship between leaf photosynthesis soon after herbicide treatment and subsequent plant mortality, with the aim of determining whether the former could predict the latter. Data from 28 glasshouse experiments were analysed. In these experiments, herbicides from five modes of action groups were tested on five plant species. Leaf photosynthesis was measured with two mobile meters up to 1 week after herbicide treatment. Leaf photosynthesis was affected by plant species, leaf number, herbicide species, dose and time. Large changes in leaf photosynthesis were observed with photosynthesisinhibiting herbicides, intermediate changes were noted with glyphosate, glufosinate-ammonium and sulcotrione, and no changes were detected with MCPA. Threshold values associated with plant mortality were then determined. These values can be used to assess the risk of uncontrolled weeds treated with variable herbicide doses.

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