EFFECT OF SPRAY VOLUME AND PRESSURE ON POSTEMERGENCE JOHNSONGRASS (SORGHUM-HALEPENSE) CONTROL

Fenoxaprop, fluazifop/fluazifop-P, haloxyfop, and quizalofop at 0.14 k g ai ha-1 and sethoxydim at 0.28 kg ai ha-1 were applied broadcast ove r-the-top in spray volumes of 94 and 374 L ha-1, each at 138 and 345 k Pa, to control johnsongrass in soybeans over a 5-yr period. The two sp ray volumes provided equal control, but control was better when treatm ents were applied at 345 kPa than at 138 kPa. There were no significan t interactions among herbicides, spray volumes, or spray pressures. Mo st of the spray was deposited on the upper surface of the plant canopy . Less than 10% of the herbicide spray applied penetrated into the can opy onto water-sensitive spray cards located 10, 20, 30, or 40 cm abov e the ground.