Flooding soil with 5 to 10 cm of water for 7 to 14 days killed all freshly planted johnsongrass (Sorghum halepense (L.) Pers.) rhizomes in greenhouse and field experiments. A delay in flooding until culms emerged greatly reduced control. Flooding the soil in which 4-week-old johnsongrass plants grew had little effect at 15 C, but plants were killed after 8 weeks of flooding at 40 C. Death of buds on immersed johnsongrass rhizomes occurred more rapidly at 40 C than at 10, 20, 25, or 30 C. Flooding for 8 days at 40 C killed all rhizomes, but 16 days of flooding were required to kill all rhizomes at 30 C. Few buds were killed when flooded at 10 or 20 C, but germination was delayed. Immersing rhizomes in water and soil provided better control than immersing them in water without soil.