Texas--or cotton--root rot fungus contaminates soils across Texas and the Southwestern United States. It affects thousands of plant species. Most damaging to cotton crops, the fungus also has a significant commercial impact on peach, rose, grape and apple crops, according to the "Texas Handbook Online." Texas root rot requires several approaches to minimize its effects.
Phymatotrichum omnivorum, the soil fungus responsible for Texas root rot, is most common in the black clay soils of Central Texas. As early as 1930, the disease was reported in 67 counties between the Red River on the Oklahoma border and the Rio Grande Valley in the southernmost part of the state.
Texas soil harbors three forms of the root rot fungus, according to the Texas A&M Department of Plant Pathology and Microbiology. The fungi's hyphae are strands that spread along plant roots to just beneath the soil surface, where they produce cotton-like, bark-destroying growths before entering the plant's vascular system. When the plant dies, fungal sclerotia grow inside the hypahe strands, where they can survive for years. In warm, wet conditions phymatotrichum also grows in spore mats on the soil surface. The light-colored mats have large, branched strands up to 16 inches across.
The hyphae on decayed plants spread through the soil to nearby plants, says the University of Arizona Cooperative Extension's plant pathologist Mary Olson. Although phymatotrichum doesn't produce airborne spores, infected plants moved from one location to another will also spread the disease. In cotton plantings, the fungus can spread as much as 30 feet in a single year.
Symptoms appear between June and September. The first symptom is leaf yellowing. Upper leafs wilt in one to two days after yellowing and lower leaves within three. Cotton plants die suddenly after their leaves have wilted. Their foliage does not drop. Trees and shrubs infected with the fungus may take longer to die.
No Texas root rot eradication program exists. However, multiple step strategy will limit its spread. It includes defining the fungus-infected areas, harvesting crops and shredding the plant stalks if appropriate. Plow the soil to a depth of 6 to 10 inches, wait two weeks, and then ready the soil for sorghum or corn planting the following season. Add the highest recommended amount of sorghum or corn fertilize and use ammonia to supply nitrogen. Following the sorghum or corn harvest, prepare the soil for an early spring planting of a rapidly maturing cotton variety. After the cotton harvest, repeat the cycle on fungus-infested areas.