Symptom Identification of Pecan Phymatotrichopsis Root Rot

Commonly known as cotton root rot or Texas root rot. PRR is caused by the soilborne fungus Phymatotrichopsis omnivora. PRR is geographically limited to the southwest and parts of the south central US and northern Mexico. The fungus persists as sclerotia (1 to 5 mm in diameter) and mycelial strands (rhizomorph) for decades in the soil, in particular calcareous clay soils (pH range of 7 to 8.5). The fungus forms spore mats (white to tan in color and 2 to 16 inches in diameter) on the soil surface during warm, rainy weather. The spores are sterile. Spread directly to adjacent plants by fungal strands that grow through the soil. Affected areas often appear as circular patterns of dead trees. All pecan varieties are susceptible. PRR affects over 2,000 species of dicots (broadleaf plants), but does not affect monocots (grasses).