Phymatotrichum root rot is considered to be one of the most serious plant diseases with respect to host range and crop destruction. Over 2000 species of dicotyledonous plants can be affected by this disease.  This disease was first described on cotton by Pammel late in the 19th century and was called Ozonium root rot.  Since that first description, Phymatotrichum root rot has been identified by several names including cotton root rot and Texas root rot.  The causal agent of this disease is the fungus Phymatotrichum omnivorum (Shear) Duggar [syn. Phymatotrichopsis omnivora (Duggar) Hennebert.]