Diseases of ash (
Cotton (Texas) root rot
Cotton or Texas root rot is caused by the soilborne fungus Phymatotrichopsis omnivora also called Phymatotrichum omnivorum.
Ash trees, Fraxinus velutina and Fraxinus velutina ' Fan-Tex', are native to the southwestern U.S., but are moderately susceptible to cotton (Texas) root rot. The first symptom of infection is wilting of the leaves and/or a fast decline (photo 1 ). Disease may develop quickly in summer months and trees can die with leaves still on the plant in a few days. 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 the 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 qualified person make a confirmed diagnosis 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)
Links for more information:
http://ag.arizona.edu/pubs/diseases/az1124/#prrhttp://cals.arizona.edu/pima/gardening/aridplants/Fraxinus_velutina.html http://cals.arizona.edu/pima/gardening/aridplants/Fraxinus_velutina_Fan-tex.html
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January 15, 2007