Herbicides in six families were evaluated for effects on growth and solerotial production by Phymatotrichum omnivorum, Dinitroaniline and s-triazine herbicides at 0.1 to 1.0 ppm stimulated solerotial formation in soil culture at 6 wks. At 9 wks differences were not as pronounced. In a cropping sequence test in infested soils treated with trifluralin or prometryne and planted to cotton there was 55-77% Phymatotrichum root rot (PRR) during the first growth cycle and 50-57% PRR after the second cycle. When cotton followed sorghum in soils treated with propazine or dicamba there was 0 to 8% PRR. Cotton grown in untreated soils had 78% PRR.