Invasive White Sweetclover (Melilotus officinalis) Control With Herbicides, Cutting and Flaming

Authors: Conn, Jeffery; Seefeldt, Steven

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2009
Publication Date: 7/20/2009
Citation: Conn, J.S., Seefeldt, S.S. 2009. Invasive White Sweetclover (Melilotus officinalis) Control With Herbicides, Cutting and Flaming. Journal of Invasive Plant Science and Management. 2:270-277.

Interpretive Summary: White sweetclover is spreading in urban areas, roadsides and glacial floodplains in Alaska and effective methods are needed to limit competition and to eradicate new populations. White sweetclover is a biennial and populations can contain either all 1st-year, all-2nd-year or mixed-age plants. We studied the effectiveness of the herbicides chlorsulfuron, 2,4-DB, clopyralid, dicamba + diflufenzopyr, triclopyr, and 2, 4-D for controlling seedling white sweetclover using greenhouse studies. All herbicides except 2,4-DB reduced dry matter of seedlings at rates below recommended doses. Based on these results, we studied the ability of chlorsulfuron, clopyralid, triclopyr and 2,4-D to control established white sweetclover plants in the field. Efficacy of flaming and cutting were also investigated. In the field, none of the herbicides reduced white sweetclover biomass in 2006, but in 2007, all the herbicides reduced biomass, especially chlorsulfuron and 2,-D at recommended rates (17.6 and 1600 g ai/ha) with 97% and 90% control. Clopyralid and triclopyr at recommended rates (210 and 1260 g ai/ha) and at 1/2X reduced viable seed production, but only chlorsulfuron at 17.6 g ai/ha eliminated viable seed production. Flaming killed 1st –year white sweetclover but some 2nd year plants resprouted and viable seed was produced. Cutting white sweetclover at either 2.5 or 10 cm height above ground did not effectively control of 1st-year plants due to regrowth from below the cut. Density and viable seed production of 2nd-year plants was reduced by cutting at 2.5 cm but not by cutting at 10 cm above the ground.

Technical Abstract: White sweetclover is invading Alaska natural areas and control methods are needed. Chlorsulfuron, 2,4-DB, clopyralid, triclopyr, and 2, 4-D controlled white sweetclover seedlings below recommended rates. None of the herbicides reduced established white sweetclover biomass in 2006, but all herbicides did in 2007, especially chlorsulfuron at 17.6 g ai/ha and 2,4-D at 1600 g ai/ha providing 97% and 90% control. Both clopyralid and triclopyr at recommended rates (210 and 1610 g ai/ha) and at ½ rates caused reductions in viable seed production but only chlorsulfuron at 17.6 g ai/ha (recommended rate) eliminated seed production. Flaming killed 1st year plants but some 2nd year plants resprouted and produced viable seed. Cutting at 2.5 or 10 cm height did not control 1st-year plants due to regrowth and 2nd year plant density and seed production was reduced by cutting at 2.5 cm but not by cutting at 10 cm.