Effect of integrated management on purple blotch (Alternaria porri (Ellis) Cif.) progression and bulb yield of onion at Arba Minch in Southern Ethiopia

Abstract

A field experiment was conducted at Arba Minch area, southern Ethiopia during the 2018 and 2019 cropping seasons to determine the integrated effects of varieties and fungicide spray frequencies on onion purple blotch (PB) epidemics, bulb yields, and economic returns. Fifteen treatment combinations consisting of three onion varieties and five fungicide spray frequencies were arranged in a factorial experiment in a randomized complete block design with three replications. Integrating varieties with fungicide spray frequencies significantly reduced onion PB epidemics and increased bulb yields and economic returns. Due to four times spray of ridomil gold (RG) at 14-day interval, PB severities as low as 35.7, 42.2, and 58.9% were recorded on Nasik-Red, Bombay-Red, and Adama-Red varieties, respectively. The lowest area under the disease progress curve of 625.3, 706.7, and 1131.1%-days was also recorded on Nasik-Red, Bombay-Red, and Adama-Red varieties, respectively, due to four sprays of RG at a 14-day interval. Three times spray of RG at 10-day interval gave the highest bulb yields of 33.4, 38.9, and 23.7 t ha-1 on Nasik-Red, Bombay-Red, and Adama-Red varieties, respectively. The results showed the existence of variability in onion genetic resistance that was complemented by fungicide spray frequencies against PB epidemics to increase bulb yields. The use of Bombay-Red variety along with three and four-time spray frequency of RG was found to be the most effective option in reducing PB epidemics and increasing onion bulb yields. However, the use of Bombay-Red variety along with three-time spray frequency of RG could be recommended, because of its highest economic returns, to farmers in the study areas and elsewhere with similar agro-ecologies to manage PB and sustain onion production and productivity in the country.