Diseases of pecan (
Cotton (Texas) root rot
Cotton or Texas root rot is caused by the soilborne fungus Phymatotrichopsis omnivora also called Phymatotrichum omnivorum. Pecan is moderately susceptible in Arizona. The first symptom of infection is wilting of the leaves or a fast decline. Disease may develop quickly in summer months and trees die in a few days with leaves still on the plant. P. omnivora infects roots of yong trees as well as mature plants and causes rotting of the roots. It grows as mycelial strands (photo 1 ) on the root surface and is readily identified by microscopic observation of its cross-shaped hyphae (photo 2 ) that are found emerging from strands.
In Arizona, records of cotton (Texas) root rot on pecan are more common in newly planted trees during the first 5 years, especially in high risk areas such as the Santa Cruz and Verde River Valleys. Mature trees seem to be fairly tolerant in most locations in Arizona.
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)
1
2 
April 2, 2007