The purpose of this study was to assess the biocontrol efficacy of the fungus Trichoderma virens in combination with fungicides against cotton (Gossypium hirsutum) seedling disease pathogens in the field under different soil and ambient environmental conditions. Cotton seed treated with fungicides and/or coated with a latex sticker and air-dried granules of T. virens was planted in field plots with a history of seedling disease in California (CA), Oklahoma (OK), Arkansas (AR), Louisiana (LA), Mississippi (MS) and Indiana (IN), and surviving seedlings counted. Seedling stands in CA from T. virens plus metalaxyl-treated seed plots were greater than the untreated control and most of the plots in which seed was treated only with fungicide. In AR and MS, T. virens plus metalaxyl treatments produced significantly better stands than the untreated controls. In some cases, this combination produced stands equal to those in fungicide-treated controls. In LA, OK, and IN, T. virens plus metalaxyl-treated seed resulted in stands equal to those in untreated controls, but less than those in the fungicide-treated controls. The addition of triademenol or fludioxonil to the seed treatment combinations did not improve stands above T. virens plus metalaxyl alone. The treatment of cotton seed with T. virens plus metalaxyl generally resulted in greater seedling stands than those in untreated controls and equal to those of the fungicide control, except where disease pressure is very heavy (IN) or light (LA and OK).
