Phymatotrichum omnivorum causes substantial losses in cotton lint yields on many soils of the Southwest. Surveys of the soil-plant ecosystems in cotton fields exhibiting Phymatotrichum root rot (PRR) on cotton and those having a history of no disease problem suggested a strong association between topographical elevations, particle size distribution and soils being suppressive or supportive of this pathogen. Aerial infrared photography and visual inspections were used to document PRR affected soils producing cotton and the nutritional status of grain sorghum crops seeded on identical soils. Results of these aerial and ground observations strongly indicated an association between levels of iron (Fe) deficiency chlorosis and other micronutrient deficiencies on this monocot and the severity of PRR incidence on cotton. Validation of field observations through soil sample analyses proved that at least two plant nutrients, iron (Fe) and magnesium (Mg) and possibly others including zinc (Zn) and Nickel (Ni) are usually present in short supply in these problem soils. Field studies were conducted evaluating various organic, biological, cultural and chemical methods for effects on the disease. Ammoniacal form of nitrogen reduced the severity of the disease while the nitrate form increased plant mortalities. Stem drenching with Fe chelate, propiconazole (fungicide) or lithium chloride were effective in suppressing PRR. Nickel applied as foliar spray or in the seedrow at planting appeared to reduced disease intensity. Additional materials evaluated in the field included the fungicides, cyproconazole and iprodione. These materials were evaluated under field conditions during this past season. Iron chelate (Fe-EDDHA) applied in the seedrow reduced plant kill to 36% compared to 61% for the control. Controlled-release propiconazole had the greatest effect with plant mortalities of only 10%. Cyproconazole appeared to perform similarly to propiconazole.