Fungicide Evaluation for the Management of Stemphylium Leaf Blight (Stemphylium vesicarium) on Onion (Allium cepa L.)

Onion (Allium cepa L.) is among the most important cash crops in Ethiopia. Over 97% of the harvest is meant for sales; it is commercially driven. Despite this huge economic value, its production and productivity are hampered by disease and insect pests. Stemphylium leaf blight (Stemphylium. vesicarium Wallr E.G.(Simmons), among others, is a newly recurring foliar disease that caused significant yield loss since its recognition in the country. Yet, there is no well-established management option. Therefore, this study was conducted to evaluate fungicides as an urgent means to mitigate its impact.  A field experiment consisting of 12 selected fungicides along with unsprayed control were evaluated at Melkassa agricultural research center in 2020 and 2021.  Percent disease index (PDI) and area under disease progress curve (AUDPC) were used to measure the disease suppression effect of the fungicides. The potential onion bulb yield loss due to the disease was estimated. Essence 38 WG highly suppressed the disease (PDI=51.54%, 44.00%) in 2020 and 2021 years, respectively, where consistently highest onion bulb yield of 359.56 Ql/ha and 257.58 Ql/ha was attained from. It was found at par with Diprocon (PDI=53.53% in 2020 and 48.0% in 2021). The apparent infection rate was steady in Essence 38 WG, Diprocon 30 EC and Rova 75% WP sprayed plots. The disease progress curve attained sigmoid shape in most of the tested products.  The disease could cause an estimated potential onion bulb yield loss of 31.9% to 39.0% if not managed. Therefore, this huge yield loss could be reduced if the above promising fungicides are augmented with other disease management options, for instance, resistant varieties like Nafis red which the research system is currently pushing to popularize to end users.