Integrated Management of Tomato Late Blight [Phytophthora infestans (Mont.) de Bary] Through Host Plant Resistance and Reduced Frequency of Fungicide in Arbaminch Areas, Southern Ethiopia

A field experiment was conducted at Arbaminch Agricultural Research Center’s of Sub-center (Chano Mille) during 2016 and 2017 cropping seasons, with the specific objectives to: 1) evaluate the effect of varieties by fungicide application frequencies on Phytophthora infestans epidemics in different cropping seasons; 2) determine the effects of host plant resistance and fungicide on fruit yield and yield components of tomato; and 3) determine the economics of fungicide spray for the management of tomato late blight. The treatments consisted of four tomato varieties with different level of resistance to late blight and five foliar spray frequencies (ridomil), including unsprayed plots as a control and the treatments were laid out in a factorial arrangement in a randomized complete block design with three replications. Integration of varieties and fungicide spray frequencies at 10 day interval significantly reduced late blight epidemics and increased fruit yield in both cropping season. In both cropping season, severity was highest on the susceptible variety (Melkasholla with 56.17% in 2016 and 27.41% in 2017 cropping seasons). Disease severities as low as 25.92, 31.78, 38.71 and 44.51% were recorded on ARP tomato d2, Bisholla, Roma VF and Melkasholla varieties in 2016, respectively. Whereas disease severities of 30.21, 33.35, 34.28 and 43.23% were recorded on ARP tomato d2, Roma VF, Bisholla and Melkasholla varieties, respectively, in 2017 when ridomil was sprayed four times during the growing seasons. The highest mean AUDPC values of 826.43, 1011.12, 1134.25 and 1245.52%-days were recorded from unsprayed plots of ARP tomato d2, Roma VF, Bisholla and Melkasholla varieties, respectively, in 2016, while the lowest mean AUDPC values were recorded from plots treated with four time sprays for all varieties in both cropping seasons. In 2016 and 2017 cropping seasons, three times foliar applications with ridomil proved to be an effective treatment against late blight and gave the highest (44.16 and 38.25 t ha-1) marketable fruit yields over the control yields of 22.92 and 19.59 t ha-1-, respectively. Nevertheless, marginal analysis indicated that the highest 40.00 and 41.30% marginal rates of return in comparison with unsprayed plots were obtained where ridomil was sprayed two times for ARPT tomato d2 variety for both cropping seasons as compared to other spray frequencies. In conclusion, integration of varieties and two times for resistant and moderately reistant varieties and three times for susceptible varieties with ridomil foliar sprays were found to be effective treatments in reducing tomato late blight epidemics and increasing fruit yields. Thus, it is recommended to use this spray frequency as it gave the highest protection against late blight and the highest monetary benefit as compared to the other treatments and the control. However, further extensive studies have to be undertaken for developing concrete recommendation for stabilizing tomato production in the country. Keywords: AUDPC, cropping seasons, disease severity, marginal analysis, Phytophthora infestans, ridomil sprays, tomato varieties, yield.