Cotton Root Rot
Cotton Root Rot (Phymatotrichopsis omnivora) is a very interesting soil-borne fungal disease. It is one of the more serious diseases because it can infect over 2,000 species of plants and there is no treatment. Monocotyledonous plants such as asparagus fern, lillies and grasses have field resistance but cotton, many types of crops, fruit, nut and shade trees are susceptible.
The conditions needed for this fungus to grow are very particular. Cotton root rot primarily occurs in the south and southwestern part of the United States as well as Mexico. It prefers very alkaline, calcareous, clay loam soil with a pH range of 7.0 to 8.5. The symptoms often become most obvious during the mid-to-late summer months, June through September, when soil temperatures reach at least 82.
Plant death can occur quickly but is typically slower in large trees. Yellowing of the plant occurs once infection has set in, then wilting, then browning and lastly death. The plant will retain its leaves once dead. Roots can be mushy and appear brownish to bronze with wooly strands of the fungus that may appear on the surface of the root. Sometimes after a rainfall or heavy irrigation, white fungal mats will develop on the soil surface.
Caution should be taken when removing infected plants. Tools should be thoroughly sanitized after use of removal to avoid contamination. An infected plant can create a new infection when moved to a new area, so caution should be used when handling infected plants as well as wood.
The fungus can survive for many years in the soil. This type of rot produces sclerotia, which are seed like pods that have been found up to 7’ below the surface of the ground. The sclerotia germinates and produces strands of the fungus that grow through the soil, eventually contacting plant roots. Then strands of the fungus colonize roots and use their nutrients to create more sclerotia. Soil excavation and removal is recommended for infected areas.
There is no effective control of this disease. If an infection is suspected, a person with experience in identifying this disease should be called to assess and diagnose and handle the affected plants. Be on the lookout this time of year (August) when conditions are favorable.