The effect of temperature regimes on seedling diseases of grain sorghum (Sorghum bicolor(L.) Moench), was investigated in growth cabinets and for five planting dates in field trials. The period from planting to seedling emergence was increased by low pre-emergence temperatures (<13°C), with a concomitant increase in the incidence of pre-emergence damping-off and mesocotyl discolouration. Low post-emergence temperatures also promoted mesocotyl discolouration. Infection of the mesocotyl, as opposed to infection of the primary root, produced the primary post-emergence disease symptoms and was related to reduced seedling vigour and increased post-emergence damping-off. Seedlings grown in sterilized and unsterilized soil in growth cabinets, under conditions of varying day/night temperature regimes, were compared. Variation in pre-emergence damping-off, mesocotyl discolouration, post-emergence damping-off, seedling length and seedling mass could be attributed to low temperature and host predisposition to infection by soil-borne pathogens.