White mold incidence, severity and lima bean (Phaseolus lunatus) yield response to fungicide application timing in the mid-Atlantic region of the United States

Abstract

Sclerotinia sclerotiorum (Lib.) de Bary causes white mold on lima bean (Phaseolus lunatus), resulting in significant yield and quality loss. Fungicides are widely used to manage white mold, yet there are no application-timing guidelines for lima bean. The knowledge gap impedes research for effective fungicide efficacy and for integrated management that combines fungicides with biological and cultural practices. Trials to determine the optimum timing for fungicide application were conducted from 2014 to 2017 with Endura 70WG (0.76 kg ha−1; a.i. boscalid) at four locations in the mid-Atlantic region. Fungicides were applied (i) at approximately 20% bloom initiation when at least 20% of plants had opened flowers; (ii) approximately one week later at 100% bloom initiation when 100% of plants had opened flowers; (iii) approximately one week later when plants were in full bloom; (iv) approximately one week later when pods were developing; (v) a double application at 20% and 100% bloom initiation; and (vi) non-sprayed [non-treated control (NTC)]. White mold incidence as number of infected plants m−1 of row, white mold severity as percentage of infected tillers per plant m−1 of row and yield (kg) from 2.3 m2 subsection of row area were recorded. Double applications at 20% and 100% bloom initiation resulted in the greatest reduction in white mold incidence and severity in most environments. However, the Endura applications one and two weeks after 100% bloom initiation reduced disease incidence by 50% and 54% in 2016 and white mold severity between 63% and 79% in 2015 and 2016. This research will provide a foundation for the development of fungicide application guidelines, and for research on use of fungicides in integrated white mold management programs for lima bean.