Variable Response of Creeping Bentgrass Cultivars to Metamifop.

Experiments were conducted at the Plant and Soil Science greenhouse facility in Lubbock, TX on bentgrass cultivars seeded on August 26, 2011. Herbicides were applied on December 1, 2011 and consisted of metamifop at 200, 300, 400, and 500 g ai ha^-1. A sequential application of each treatment was made December 22, 2011. Percent bentgrass phytotoxicity was recorded weekly on a scale of 0 to 100%. Clipping weights were recorded 3 and 6 WAIT. Metamifop at 200 to 300 g ai ha^-1 exhibited 0 to 7% bentgrass phytotoxicity 3 WAIT, regardless of cultivar. Metamifop at 400 to 500 g ai ha^-1 exhibited 11 to 21% phytotoxicity on ‘L-93’ and ‘Penn A-4’, while phytotoxicity on all other cultivars was ≤ 9% 3 WAIT. Phytotoxicity observed on ‘L-93’ and ‘Penn A-4’ in response to metamifop at 400 to 500 g ai ha^-1 coincided with large reductions in biomass (71 to 84%) compared to the untreated checks 3 WAIT. All bentgrass cultivars exhibited ≤ 11% phytotoxicity in response to metamifop at 200 g ai ha^-1 6 WAIT. Bentgrass cultivars responded differently to applications of metamifop at 300 g ai ha^-1 6 WAIT. Phytotoxicity was only 10% for ‘Crystal Bluelinks’, 19% for ‘Seaside II’, 20% for ‘SR7200’, and 29% for ‘T-1’. Phytotoxicity was 44 to 78% for the remaining cultivars 6 WAIT. ‘Seaside II’, ‘SR7200’, ‘T-1’, and ‘Crystal Bluelinks’ exhibited 22 to 35% phytotoxicity in response to metamifop at 400 g ai ha^-1 6 WAIT, while all other cultivars exhibited 68 to 88% phytotoxicity. ‘Seaside II’, ‘SR7200’, and ‘Crystal Bluelinks’ exhibited 48 to 50% phytotoxicity in response to metamifop at 500 g ai ha^-1 6 WAIT, while all other cultivars exhibited 66 to 86% phytotoxicity. High levels of phytotoxicity 6 WAIT coincided with large amounts of biomass reduction when compared to the untreated checks.