Differential Response of Four Trifolium Species to Common Broadleaf Herbicides: Implications for Mixed Grass-Legume Swards

Clovers are commonly included as utility plants within mixed grass swards, such as pastures and roadside right-of-ways. As such, they provide supplemental nitrogen, quality forage, and insect habitat. Yet weed control within mixed swards is often hampered by the lack of selective herbicides that are tolerated by clovers. Differential tolerance of legumes to common row-crop and pasture herbicides has previously been reported, yet little information is available that is specific to clover species. Herbicide injury of clover is often inconsistent, hypothetically due to differential species tolerance. Field and greenhouse experiments were conducted with the objective of testing differential tolerance amongst four clover species. Our experiments suggest varying tolerances amongst clover species and common broadleaf herbicides. Only imazaquin control differed due to species; however, treatment by clover interactions were further demonstrated due to variable reductions in clover height. Imazaquin, 2,4-D, 2,4-DB, and triclopyr height reductions differed due to clover species. Differential clover response to herbicide treatment should be an important consideration when managing mixed grass–clover swards and should be accounted for in future research. On a more practical level, our experiments demonstrate a range of herbicides that effectively control clover species, including atrazine, dicamba, clopyralid, 2,4-D, triclopyr, metsulfuron, and trifloxysulfuron. However, results suggest that 2,4-DB, imazethapyr, and bentazon are candidate herbicides for weed control in scenarios in which clover is a desirable crop.Nomenclature: 2,4-D; 2,4-DB; atrazine; bentazon; clopyralid; dicamba; imazaquin; imazethapyr; MCPA; metsulfuron; triclopyr; trifloxysulfuron; ball clover, Trifolium nigrescens Viv.; crimson clover, Trifolium incarnatum L. TRFIN; small hop clover, Trifolium dubium Sibth. TRFDU; white clover, Trifolium repens L. TRFRE.