Effect of Spray Volume and Pressure on Postemergence Johnsongrass (Sorghum halepense) Control

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Abstract
Fenoxaprop, fluazifop/fluazifop-P, haloxyfop, and quizalofop at 0.14 kg ai ha−1and sethoxydim at 0.28 kg ai ha−1were applied broadcast over-the-top in spray volumes of 94 and 374 L ha−1, each at 138 and 345 kPa, to control johnsongrass in soybeans over a 5-yr period. The two spray volumes provided equal control, but control was better when treatments were applied at 345 kPa than at 138 kPa. There were no significant interactions among herbicides, spray volumes, or spray pressures. Most of the spray was deposited on the upper surface of the plant canopy. Less than 10% of the herbicide spray applied penetrated into the canopy onto water-sensitive spray cards located 10, 20, 30, or 40 cm above the ground.