Field performance of a red clover germplasm selected for increased tolerance to 2,4-D

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Abstract
This study compared the field performance of red clover germplasm UK2014, selected for 2,4-D tolerance, to Kenland, a standard variety grown in the transition zone of the United States. UK2014 and Kenland were seeded in the spring of 2017 and 2018. Single applications of 0, 1.12, or 2.24 kg ae ha−1 2,4-D-amine were made in June, August, or October. One week after the treatments, yields were determined. Visible herbicide injury ratings were made prior to harvest and regrowth was visibly assessed 1 wk after harvest. Red clover stands were visibly assessed the following spring. Kenland, across all application timings, was injured by 2,4-D more than UK2014, with mean injury ratings of 39% and 63% compared with 26% and 37% at 1.12 and 2.24 kg 2,4-D ae ha−1, respectively. At equivalent rates, Kenland regrowth was less than UK2014 at all application timings. UK2014 regrowth after 2,4-D treatment ranged from 65% to 91%, whereas Kenland regrowth ranged from 12% to 72%. Applications of 2,4-D in October were the most damaging to stands of both UK2014 and Kenland the following spring, but Kenland stands were reduced much more than those of UK2014. Kenland and UK2014 had similar season total yields when not treated with 2,4-D (means of 7,550 and 7,880 dry matter kg ha−1, respectively in 2017 and 5,280 dry matter kg ha−1 for both in 2018). Kenland season total yield in 2017 was reduced by both 2,4-D rates applied in June or August and at all timings in 2018. UK2014 season total yield in 2017 was reduced only when 2.24 kg 2,4-D ae ha−1 was applied in August. In 2018, 2.24 kg ae ha−1 2,4-D resulted in reduced UK2014 season total yield across application timings. UK2014 has greater 2,4-D tolerance than Kenland, but additional selection might be beneficial.

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