Evaluation of Fungicides with the Combinations of Potato (Solanum tuberosum L.) Varieties to Manage Late Blight (Phytophthora infestans (Mont) de Bary) in Highlands of Guji Zone, Southern Ethiopia

Potato late blight (Phytophthora infestans (Mont.) de Bary) is one of the most devastating plant diseases world-wide and is feared globally by farmers and industry. There is little information on the type of fungicide to be sprayed to control late blight for optimum production of the crop in the study area. Therefore, an experiment was conducted at Bore Agricultural Research Center, Southern Ethiopia during the 2015 and 2017 cropping season to evaluate fungicides with the combination of Potato varieties to manage late blight and to assess the cost and benefits of different fungicides on Gudanie and Jalenie potato varieties. The treatments consisted of two (2) Potato varieties Gudanie and Jalenie currently under production but differ in their late blight reaction and three (3) fungicides Ridomil Gold MZ 63.5%WP, Mancozeb 80% WP2 and Matico and one (1) unsprayed treatments were used as experimental materials. The experiment was laid out as a Randomized Complete Block Design (RCBD) in a 4 x 2 factorial arrangement and replicated three times per treatment. The improved potato varieties called Gudanie and Jalenie were planted as the test crop in a plot size of 3 m * 2.1 m with intra and inter-row spacing of 0.30 and 0.75 m respectively. Data were collected on growth, yield, yield components and disease incidence and severity. The two years combined data analysis results revealed that the interaction effect of fungicides and potato varieties had influenced significantly (P<0.05) response on days to 50% flowering, 50% maturity, plant height, number of tubers per hill, stem number per plant, marketable tuber yield and unmarketable tuber yield and total tuber yield. However, interaction effect of fungicides and potato varieties had non-significant (P>0.05) effect on days to50% emergency and average tuber weight. The two year data analysis the highest (47.34 t ha-1and 46.31 tha-1) marketable tuber yield was obtained from Gudanie variety with Ridomil Gold fungicide spraying at Bore on-station and Ana sora on-farm both locations respectively. The result of 2015 year disease data indicates that maximum (59.52% and 3.67) disease incidence and severity, respectively was recorded by unsprayed treatment of Jalenie variety and also the second year maximum (45.24 % and 2.83) disease incidence and severity by treatment Gudanie variety unsprayed fungicides, respectively. However, the minimum (5.48% and 1.16) disease incidence and severity of late blight was recorded by spraying Ridomil Gold on both Gudanie and Jalenie varieties in 2015 cropping season, respectively. In general, spraying of Ridomil Gold fungicide was more effective by reducing the disease severity and increasing tuber yield. The partial budget analysis revealed that application of Ridomil Gold on Gudanie variety resulted the highest net benefits of Birr 244,462.50 and 235,352 ha-1 with an acceptable marginal rate of returns (MRR) of 2549.00 and 2698% . Thus, application of Ridomil Gold on Gudanie variety led to optimum marketable tuber production and economic returns. Therefore, the farmers’ in highlands of Guji zone and similar agro-ecology can produce healthy and maximum potato crop of Gudanie by spraying Ridomil Gold fungicide with the recommended rates and frequency. Keywords: Disease severity and incidence, Sprayed and Unsprayed plot, Marketable tuber yield and Partial budget analysi