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White mold incidence, severity and lima bean yield response to fungicide application timing in the Mid-Atlantic Region

Habtamu Demissie: PhD Student at the University of Maryland

<div><em>Sclerotinia sclerotiorum</em> (Lib.) de Bary causes white mold disease, which results in high yield loss on lima bean. Fungicides with active ingredients boscalid (Endura 70W) or thiophanatemethyl (e.g. Topsin M) are currently used to manage white mold, yet no specific application guidelines exist for lima bean in the Mid-Atlantic region. Efficacy trials were conducted from 2014 – 2017 with Endura (0.76 kg ha<sup>-1</sup>) fungicide at four locations in Delaware. Treatments included fungicide application timing at 20% flowering; one week later; two weeks later; three weeks later; at 20% flowering plus one week later (double treated); and non-sprayed. Disease incidence (DI) was measured as the number of infected plants m<sup>-1</sup> section of row. Disease severity (DS) was rated as percentage of infected tillers per plant within each m section. Lima bean yield was recorded as kg from 6 m<sup>2</sup> subsection of row area. All data were analyzed using Proc GLM in SAS. Both DI (<em>P</em><0.0005) and DS (<em>P</em><0.0002) were significantly influenced by fungicide application timings and years. There were significant (<em>P</em><0.0001) interactions between the application timing and years. Double treated was the best application timing, and significantly reduced the DI and DS compared to the non-sprayed plots and those sprayed three weeks after 20% flowering. Yield was significantly (<em>P</em><0.0001) different between locations and years. There was significant (<em>P<</em>0.015) but weak negative correlation (r = - 0.187) between DI and yield.</div>