Effects of temperature, sunlight, soil incorporation and surface irrigation on the phytotoxicity of oryzalin (3,5-dinitro-N4,N4 -dipropylsulfanilamide) were studied. The activity of oryzalin applied 4 to 6 weeks prior to planting was enhanced by covering the soil with plastic as measured by the inhibition of grain sorghum [Sorghum bicolor (L.) Moench. 'Sexauer G-701′] root growth. Growth chamber studies demonstrated that oryzalin phytotoxicity to grain sorghum was greater at 20 and 25 C than at 30C. The control of foxtail millet [Setaria italica (L.) Beauv. #5 SETIT] bristly foxtail [Setaria verticillata (L.) Beauv. # SETVE], redroot pigweed (Amaranthus retroflexus L. # AMARE), and smooth pigweed (Amarantbus hybridus L.), and injury to grain sorghum increased as the thoroughness of mechanical incorporation of oryzalin into soil increased. The phytotoxicity of surface-applied oryzalin increased with increasing amounts of irrigation water until it equaled the level of a preplant-incorporated treatment.
