The effect of foliar fungicide application timing on the control of dry bean anthracnose

Abstract

Gillard, C. L., Ranatunga, N. K. and Conner, R. L. 2012. The effect of foliar fungicide application timing on the control of dry bean anthracnose. Can. J. Plant Sci. 92: 109–118. Anthracnose caused by Colletotrichum lindemuthianum is a major disease of dry bean (Phaseolus vulgaris L.), reducing seed quality and yield. A study carried out in 2005 and 2006 at Exeter, ON, and at Morden, MB, determined that a sequential application of fungicide at the correct time is crucial for the effective management of the disease. The effect of the fungicides azoxystrobin and pyraclostrobin at four single foliar application timings at 5th trifoliolate (A), 1st flower (B), full flower (C) and 10 d after full flower (D) and at three sequential timings (A+C, B+C, and B+D) were evaluated under low and high disease pressure conditions. Data were collected on leaf vein and pod infection, plant maturity, dockage, pick, seed weight, yield and return on investment. Results were analyzed using analysis of variance (ANOVA) and contrast comparisons were carried out for various treatment combinations. Differences between the two fungicides for leaf symptoms were not apparent under low disease pressure, but occurred early in plant development under high disease pressure. Pyraclostrobin-treated plots produced a higher yield under high disease pressure and better quality seeds at both high and low disease pressure conditions. A single fungicide application at the A timing gave higher yield under low disease pressure, while timings B and C gave a higher yield under high disease pressure. A sequential application often provided greater anthracnose control and improved yield and seed quality, compared with single application timings. For the sequential application timings, the highest yields occurred at the A+C timing under low disease pressure, and at the A+C or B+C timing under high disease pressure.