Diseases of Pima cotton (Gossypium barbadense) ; upland cotton (G. hirsutum)
Cotton root rot
Root rot of cotton is caused by the soilborne fungus Phymatotrichopsis omnivora (Phymatotrichum omnivorum). The first symptom of infection is wilting of the upper leaves (photo 1). Disease may develop in the field in small areas or in large, circular areas in which most plants die (photo 2). P. omnivora infects roots of mature plants and causes rotting of the entire tap root. It grows as mycelial strands on the root surface and is readily identified by microscopic observation of its cross-shaped hyphae (photo 3) that are found emerging from strands. There is no resistance to root rot in cotton, and there are no controls other than long term rotations with immune crops such as winter grains and sorghum. For more information concerning cotton root rot on other hosts (see Cotton Root Rot bulletin Az1150).
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October 13, 2008