Diseases of oleander (
Cotton (Texas) root rot
Root rot of oleander is caused by the soil borne fungus Phymatotrichopsis omnivora (Phymatotrichum omnivorum). Oleanders are very susceptible to cotton (Texas) root rot (photo 1). The first symptom of infection is wilting of the leaves or a fast decline. Disease may develop quickly in summer months and plants die with leaves still on the plant. P. omnivora infects roots of mature plants and causes rotting of the entire tap root. It grows as mycelial strands (photo 2) 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 cotton (Texas) root rot, and there are no prevention or control measures that are consistently effective. It is very important that a confirmed diagnosis be made by a qualified person since other problems such as poor irrigation can cause similar symptoms. If cotton (Texas) root rot is diagnosed, tolerant and immune plants only should be replanted in the area (see Cotton Root Rot bulletin AZ1150).
February 21, 2013