Integrated management of angular leaf spot (Phaeoisariopsis griseola (Sacc.) Ferr.) on snap beans in Ontario.
Angular leaf spot (ALS) caused by the fungus Phaeoisariopsis griseola was first observed and confirmed on snap beans (Phaseolus vulgaris) growing in 3 commercial fields in southern Ontario, Canada during the 2000 growing season. The potential impact of this disease on the bean industry in Ontario is not known but this disease is severe in many other regions. The objective of this study was to develop a disease management strategy for ALS in Ontario by investigating the survival of P. griseola and assessing the influence of bean cultivars and fungicides on disease development. P. griseola survived at least one winter on crop debris in Ontario and survived better on the soil surface in comparison to burial in soil at depths of 5 or 25 cm. Fifteen snap bean cultivars were compared for susceptibility to ALS in a growth room, and 9 cultivars were compared in a naturally-infested field from 2001-03. Most cultivars reacted similarly to P. griseola in both environments. For example, the cultivars Carlo, Storm, and Bush Blue Lake 47 were least susceptible, whereas Gold Rush was most susceptible in field and growth room experiments. Boscalid, pyraclostrobin, pyramethanil, vinclozolin, and thiophanate-methyl were tested for effectiveness in managing ALS under field conditions. Overall, pyraclostrobin was most effective. Results indicate that an effective disease management strategy for ALS in snap bean in Ontario should include burying infested plant debris through deep ploughing, crop rotation for 2 years, growing the least susceptible cultivars, and applying a registered effective fungicide.