Phymatotrichopsis Root Rot in Pecan

Phymatotrichopsis root rot (abbreviated as PRR) is commonly referred to as Cotton root rot, Phymatotrichum root rot, Texas root rot, or Ozonium root rot. This disease is caused by a soilborne fungus Phymatotrichopsis omnivora (abbreviated as PO) that attacks the roots of susceptible plants, causing sudden wilt and death. This pathogen has a wide host range and can attack more than 2,300 dicotyledonous (broadleaf) plant species including many ornamental and important agronomic crops (Lyda, 1978). In contrast, the fungus colonizes but does not kill monocotyledonous plants (grasses), which are highly tolerant or resistant to this pathogen. Phymatotrichopsis can be found in a wide range of soils, but is more prevalent in calcareous clay soils with a high pH range of 7.0 – 8.5. It is one of the most destructive fungal pathogens of pecan, pistachio, cotton, alfalfa, grape, fruit trees, shade trees, and ornamental plants like conifers. The economic losses attributable to this important disease are over hundreds of millions of dollars annually in the southwestern and south central United States (www.cotton.org).