Integrated Management of Angular Leaf Spot (Phaeoisariopsis griseola (Sacc.) Ferr.) on Snap Beans in Ontario

Abstract

Angular leaf spot (ALS) caused by the fungus Phaeoisariopsis griseola (Sacc.) Ferr. was first observed and confirmed on snap beans growing in three commercial fields in southern Ontario 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 in Ontario, and assessing the influence of bean varieties 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 varieties were compared for susceptibility to ALS in a growth room, and nine varieties were compared in a naturally-infested field from 2001-2003. Most varieties reacted similarly to P. griseola in both environments. For example, the varieties 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 plowing, crop rotation for two years, growing the least susceptible varieties, and applying a registered effective fungicide. Accepted for publication 13 October 2005. Published 29 November 2005.