Forage Legume Response to Dicamba and 2,4‐D Applications1

AbstractWeed control options in pastures containing legumes are limited due to herbicide selectivity. A field study was conducted for 2 years in northeast Mississippi on a Leeper fine sandy loam (fine, montmorillonitic, nonacid, thermic Vertic Haplaquept) soil to evaluate tolerance of subterranean (Trifolium subterraneumL.), white (T. repensL.), crimson (T. incarnatumL.), red (T. pratenseL.), and arrowleaf (T. vesiculosumSavi) clovers and vetch (Vicia sativaL.) to dicamba (3,6‐dichloro‐o‐anisic acid), 2,4‐D [(2,4‐dichlorophenoxy) acetic acid], and a 3:l (W:W) mixture of 2,4‐D + dicamba. Stands of all clover species were generally reduced where dicamba at 0.56 kg ha−1and where 2,4‐D + dicamba at 0.42 + 0.14 or 0.84 + 0.28 kg ha−1were applied. Forty‐five days after herbicide application legume yields, with the exception of crimson clover, were reduced at least 24% when treated with dicamba. Yields of all clover species were severely reduced where 2,4‐D + dicamba was applied ranging from 50% for subterranean to 84% for red clover. Subterranean clover yield was not affected and white clover yield was only slightly reduced (28%) where 2,4‐D at 1.12 kg ha−1was applied; yields of other clover species were markedly reduced. Vetch was killed with all herbicides applied. To determine residual activity, bermudagrass [Cynodon dactylon(L.) Pers.] sod was treated with dicamba and 2,4‐D + dicamba 120, 90, 60, 30, and 15 days prior to overseeding crimson and white clover on 1 October. The study was conducted for 2 years on a Leeper fine sandy loam soil. Application time of dicamba at 0.28 kg ha‐1and 2,4‐D + dicamba at 0.42 + 0.14 kg ha−1did not affect crimson or white clover yields measured in mid‐May. However, crimson and white clover yields were reduced an average of 39 and 55% where dicamba was applied at 0.56 and 1.12 kg ha−1, respectively, and 37% when 2,4‐D + dicamba was applied at 1.68 + 0.56 kg ha−115 days prior to overseeding compared to 30 days. Selective broadleaf control can be obtained by using 2,4‐D at 1.12 kg ha−1in pastures containing subterranean and white clover. Dicamba at 0.56 kg ha−1or 2,4‐D + dicamba at 1.68 + 0.56 kg ha−1should be applied to warm‐season grass pasture at least 30 days prior to overseeding in order to avoid residual activity on overseeded legumes.