Abstract

Preemergent herbicides that effectively control hairy bittercress are not labeled for use on creeping phlox. Studies were conducted to determine preemergent herbicide injury to creeping phlox varieties ‘Crimson Beauty’, ‘Emerald Blue’ and ‘Fort Hill’, and optimal herbicide rates for bittercress control. Barricade (prodiamine) applied at 0.55 kg ai/ha (0.5 lb ai/A) and Surflan (oryzalin) applied at 1.1 kg ai/ha (1.0 lb ai/A) severely injured creeping phlox. Injury was less severe from applications of Dimension (dithiopyr) at 0.83 kg ai/ha (0.75 lb ai/A), Gallery (isoxaben) at 0.55 kg ai/ha (0.5 lb ai/A), Image (imazaquin) at 0.55 kg ai/ha (0.5 lb ai/A), and Treflan (trifluralin) at 2.2 kg ai/ha (2.0 lb ai/A). Minimal to no injury was found with Pennant (metolachlor) at 2.2 kg ai/ha (2.0 lb ai/A) and Snapshot TG (isoxaben + trifluralin) at 2.8 kg ai/ha (2.5 lb ai/A). Two applications of Gallery at 0.28, 0.55 and 1.1 kg ai/ha (0.25, 0.50 and 1.0 lb ai/A), Pennant at 1.2, 2.2 and 4.4 kg ai/ha (1,2 and 4 lb ai/A), RegalKade (prodiamine) at 0.28, 0.55 and 1.1 kg ai/ha (0.25, 0.50 and 1.0 lb ai/A), and Snapshot TG at 1.4, 2.8 and 5.5 kg ai/ha (1.3, 2.5 and 5.0 lb ai/A) did not affect growth of phlox varieties at 27 weeks after treatment (WAT). However, visual injury to varieties ‘Crimson Beauty’ and ‘Fort Hill’ was detected at a greater frequency than injury to ‘Emerald Blue’. Gallery and Snapshot TG applied at 0.28, 0.55 and 1.1 kg ai/ha (0.25, 0.50 and 1.0 lb ai/A) and 1.4, 2.8 and 5.5 kg ai/ha (1.3, 2.5 and 5.0 lb ai/A), respectively, and RegalKade applied at 1.1 kg ai/ha (1 lb ai/A) provided excellent bittercress and yellow woodsorrel control at 8 and 12 WAT. Pennant did not control either weed species at the high rate. In a greenhouse study, Gallery applied at 0.14 kg ai/ha (0.13 lb ai/A) effectively controlled bittercress through 8 WAT, but Snapshot applied at the same rate of isoxaben did not control bittercress. Results indicate that Snapshot TG may be safely applied to creeping phlox at rates of 1.38 to 2.75 kg ai/ha (1.25-2.5 lb ai/A) for preemergent bittercress control. Gallery may also be used safely and effectively at rates of 0.14 to 0.28 kg ai/ha (0.13 to 0.25 lb ai/A).