Phymatotrichopsis root rot

Phymatotrichopsis root rot, frequently referred to as Texas root rot or cotton root rot, is a devastating soil-borne disease caused by the fungus Phymatotrichopsis omnivora. This pathogen attacks the vascular tissue of plant roots, effectively cutting off the supply of water and nutrients, which typically leads to the rapid death of the host plant.

The fungus exhibits a remarkably broad host range, infecting over 2,000 species of dicotyledonous plants. Key agricultural crops susceptible to this disease include cotton, alfalfa, grapes, various fruit trees, and numerous vegetable crops. Monocotyledonous plants, such as cereal grains and corn, remain immune to this specific pathogen.

Symptoms of the infection usually appear suddenly during the warm season. Leaves show signs of wilting, followed by yellowing and necrosis, while remaining attached to the stems. A diagnostic feature is found beneath the soil surface: the root bark appears rotted and is covered with distinct, tan-colored mycelial strands that resemble fungal cobwebs.

The development and spread of Phymatotrichopsis omnivora are highly dependent on environmental conditions. It thrives in alkaline, calcareous soils where temperatures are consistently high (above 25°C). The fungus survives in the soil for many years in the form of sclerotia, which are dormant, hardened structures that allow it to persist even in the absence of a host.

Management of this root rot is challenging due to the fungus's ability to survive deep within the soil profile. Prevention remains the primary strategy. Recommended practices include:

• Utilizing crop rotation with resistant monocots like wheat or corn.
• Improving soil structure and drainage.
• Removing and destroying infected plant debris.
• Applying deep plowing to disturb the fungal mycelium.