Efficacy and economics of fungicide spray in the control of late blight of potato in Ethiopia

During the 1996 and 1997 seasons research was done at Holetta on the economic benefits of integrated management of late blight using genetic resistance and chemical (preventive and /or contact) methods. Varieties Tolcha (tolerant to late blight) and AL-624 (susceptible to late blight) were studied with five chemical controls during crop development. The chemical control started immediately after the first disease symptom was observed (41days after crop emergence) and chemical control was repeated after every 7 days for contact fungicides and 21 days for preventive fungicide. In 1997 AL-624 and Tolcha received 4 -5 and 2 applications, respectively, of the protectant fungicide whereas the preventive fungicide was applied 3 and 2 times on the susceptible and tolerant variety, respectively. In 1996 all contact fungicides were applied 5 times and the preventive fungicide 2 times on AL-624 while on Tolcha it was applied 3 and 1 time, respectively. Results showed that the use of preventive fungicide like Ridomil MZ 63.5% WP and contact fungicide such as Brestan 10, Chlorothalonil and Dithane M-45 can earn potato producers above the acceptable level (100%) of marginal rate of return (MRR). Thus, both genetic resistance and chemical control provide economic options for management of late blight. Key Words: Economic benefit, fungicides, genetic resistance, Phytophthora infestans, Solanum tuberosum (African Crop Science Journal 2001 9(1): 245-250