Tolerance of direct-seeded leafy greens to herbicides applied before or after crop emergence

Field experiments were conducted in 2005 and 2006 to determine the tolerance of direct-seeded Brassica rapa L. ‘Alamo’, Brassica juncea (L.) Czernj. & J. M. Coulter var. crispifolia L. H. Bailey ‘Southern Curled Giant’, Brassica oleracea var. acephala ‘Blue Knight’, and Brassica oleracea L. var. acephala DC ‘Top Bunch’ to selected residual herbicides applied before or after crop emergence. Ten herbicides were applied at a single dose prior to crop emergence, and eight of the same herbicides were applied post-emergence relative to the crops. To allow assessment of tolerance and prevent yield loss from weed interference, the test area was kept free of weeds by cultivation and hand-weeding. Of the herbicides applied prior to crop emergence, pendimethalin at 560 g a.i./ha, thiobencarb at 1120 g a.i./ha, quinclorac at 140 g a.i./ha, and prodiamine at 515 g a.i./ha caused less than 10% injury to all crops and did not reduce density, height, or fresh weight of any of the four crops. The crops were generally more tolerant to the herbicides when applied after crop emergence than before emergence. None of the crops were injured more than 10% by S-metolachlor at 500 g a.i./ha, pendimethalin at 560 g/ha, thiobencarb at 1120 g/ha, dimethenamid at 448 g a.i./ha, and prodiamine at 515 g/ha when applied after crop emergence.