Evaluation of fungicidal spray schedules for angular leaf spot management in common beans.

Common bean (Phaseolus vulgaris) production in the tropics is usually limited by damage due to angular leaf spot (ALS) incited by Phaeoisariopsis griseola. Field trials were conducted during 2004 and 2005 in Dschang, Cameroon, to assess the economic efficacy of fungicide schedules on disease management. Each of the three cultivars received 7and 14-day, monitored sprays of thiophanate methyl (Topsin–M) or no sprays (control). Disease severity, plant growth and yield were evaluated. Economic assessments were used to determine the feasibility of the treatment options in regards to their associated costs and benefits. All fungicidal spray schedules significantly reduced ALS severity and increased leaf area index and grain yields. Seed yield increased by 66 – 80 % for monitored sprays, 83 – 159 % for fortnightly sprays and 95 – 184 % for weekly sprays. Although net returns were highest for Glp190 plots (US$ 347.6/ha) exposed to the fortnightly fungicidal spray schedules and Meringue (US$ 659.8/ha) and Ph653 (US$ 728.6/ha) plots that received nine weekly fungicide sprays, the highest returns to investment (142 – 439 %) were consistently recorded in plots that received the monitored spray schedule. Results suggest that monitoring disease progress in the field for spraying followed by routinely sprays may be the most economic disease management strategy for common bean ALS.