Technical Abstract: Pythium species cause a number of diseases on corn. Among the Pythium diseases, root rot presents the least conspicuous aboveground symptoms. Broadly defined, root rot also includes feeder root necrosis. At least 16 species of Pythium are known to cause root rot of corn. These include P. acanthicum, P. ad¬haerens, P. angustatum, P. aphanidermatum, P. arrhenomanes, P. graminicola, P. helicoides, P. irregulare, P. paroecandrum, P. pulchrum, P. rostratum, P. sylvaticum, P. splendens, P. tardicrescens, P. ultimum, and P. vexans. They generally overwinter in soil as oospores that germinate producing mycelium and sporangia. The sporangia may then produce zoospores. Mycelium, sporangia and/or zoospores all can infect corn roots causing root rot. Management of the disease include improving soil drainage, avoiding planting corn in soils, and the use of fungicides in seed treatments. However, Pythium spp. and isolates of a given species vary in their sensitivity to different fungicides. Appropriate rotation or combinations of fungicides with different modes of action should be practiced to improve control efficacy and prevent development of fungicide resistance in Pythium spp. No resistance is known in corn hybrids and rotation has not been effective in managing Pythium root rot of corn.