Field studies were conducted to determine the effect of green foxtail density and location on the yield of potato under dryland conditions. Total and marketable tuber yields were reduced by green foxtail densities of less than 75 plants m-2. Marketable yields were affected more by increasing green foxtail density than were total yields. Increasing weed density reduced both the number and size (tuber weight) of marketable tubers but not the specific gravity or the sucrose content of the tubers at harvest. Green foxtail growing between crop rows was as competitive with potato as plants growing within the row. The effect of weed competition on total and marketable tuber yields was more pronounced in drought years than years with normal precipitation.
