s and multi-locations to come up with concrete and workable recommendations. Potato (Solanum tuberosum L.) is one of the most widely grown food security crops in Farta District. However, production and productivity of the crop is low due to lack of recommendation NPS fertilizer rates and late blight disease infestations. Thus, a field experiment was conducted in 2019 cropping season in Farta District, North west Ethiopia to determine the proper time spraying of mancozeb and application of the optimum rate of NPS blended fertilizer for management of late blight disease .Factorial combination of three levels of NPS Blended fertilizer (90,180 and 270 kg ha-1) and four times of Mancozeb 80% WP fungicide application (control unspray, spraying after 45,60 and 75 days of emergence ) were laid out in randomized complete block design (RCBD) with three replications.“Belete” potato variety was used as a testing crop. Results revealed that application of NPS blended fertilizer and time of mancozeb application as main factors very highly significantly (P <0.001) influenced almost all parameters of potato, except days to emergency. Their interaction influenced also days to flowering and maturity, stem number per hill, marketable yield, unmarketable yield and total yield of potato significantly. The maximum marketable tuber yield of potato was recorded with the spraying of Mancozeb 80% WP after 45 days of emergence and application of NPS blended fertilizer at the rate of 270 kg ha-1.Partial budget analysis results also confirmed that NPS blended fertilizer application at the rate of 270 kg ha-1 and Mancozeb 80% WP fungicide spraying after 45 days of emergence gave the maximum net benefit of Birr 254,973.20 Birr ha-1. Based on the results of the present study, hence, application of NPS blended fertilizer at the rate of 180 kg ha-1 and spraying of Mancozeb 80% WP fungicide after 45 days of emergence at its recommended rate of 2 kg ha-1 is suggested foreconomically feasible and profitable for the production of potato in the study area. Since the present study was conducted in a single season and one location, it is necessary however to carry out similar studies further in different season Key words: Blended fertilizer, fungicide spraying time, late blight disease, potato, productivity