The impact of three pre-plant herbicides, trifluralin, pendimethalin and prometryn, on the incidence and the development of Rhizoctonia solani-induced cotton seedling damping-off was investigated in the controlled environmental chamber and in the field. In the controlled environmental chamber experiments, trifluralin, pendimethalin and prometryn were applied to the soil at 1.8, 2.4, and 3.6 μg a.i. g-1 soil, respectively (equivalent to the respective recommended field concentrations of 0.7, 0.9, and 1.3 kg a.i. ha-1). In the controlled environmental chamber experiments, where soil was infested at planting, application of prometryn, but not pendimethalin or trifluralin, to the soil caused a significant (P < 0.05) increase in damping-off incidence. In controlled environmental chamber experiments where soil was infested after emergence, damping-off increased significantly (P < 0.05) in the presence of pendimethalin and prometryn, but not trifluralin. In a field experiment conducted in Safford, Arizona, pre-plant application of pendimethalin or prometryn, but not trifluralin, caused significant (P < 0.05) increases in disease incidence. In another field experiment in Tucson, Arizona, a significant (P < 0.05) increase in disease incidence was observed in plots treated with prometryn, but not in plots treated with pendimethalin or trifluralin. In both controlled environmental chamber and field experiments, application of selected herbicides had significant effects on disease development as judged by the slope of disease progress curves.