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Conflict in land use between corn(Zea mays L.)as a grain crop and flue-cured tobacco(Nico-tiana tabacum L.)as an economic crop is severe because of limited arable land in mountainous regions.A field study was conducted to deter-mine the optimal planting time for corn as a relay crop in a flue-cured tobacco system to obtain high corn productivity and ensure the quality and yield of tobacco.Four relay-intercropping planting dates(10,17,24,and 31 d after tobacco apex excision)and corn monoculture(17 d after tobacco apex excision)were evaluated on the incidence and severity index of diseases and yield of corn at Chuxiong,Yunnan,China in 2010 and 2011.The incidence and severity index of corn common rust(Puccinia sorghi)were reduced 60.3 to 67.8%and 69.2 to 78.9%,respectively,by relay intercropping compared with monoculture corn.Grain yield,economic value,land equiva-lency ratio(LEr),and relative value total(rVT)of relay-intercropped corn and the net return of the whole relay-intercropping system gener-ally decreased when the relay-intercropping timing of corn was delayed.All LEr values and some of the rVT values for relay-intercropped corn were >1.Net return of the whole tobacco and corn relay-intercropping system was 18.5 to 21.0 times greater than that under monoculture corn.relay-intercropped corn after flue-cured tobacco is an economically viable cropping sys-tem in Yunnan and similar regions,with an opti-mal relay-intercropping date between 10 and 17 d after tobacco apex excision.