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Title: WEED CONTROL RESEARCH IN MINT

Author
item Boydston, Rick
item BAKER, R - WSU - PROSSER

Submitted to: Mint Industry Research Council 2002 Research Reports
Publication Type: Proceedings
Publication Acceptance Date: 11/1/2002
Publication Date: 1/1/2003
Citation: BOYDSTON, R.A., BAKER, R. WEED CONTROL RESEARCH IN MINT. MINT INDUSTRY RESEARCH COUNCIL 2002 RESEARCH REPORTS, LAS VEGAS, NV. P. 21. JAN 2003.

Interpretive Summary: Weeds lower mint oil yield and quality. Weed control represents a major production cost and investment of time for growers. The goal of this research is to develop improved weed control methods in spearmint and peppermint and to identify promising new herbicides on spearmint and peppermint. Several herbicides were identified that were safe on mint while controlling several problem weeds. Flufenacet was selective on spearmint and warrants further testing on peppermint and spearmint. Clomazone and sulfentrazone controlled two common broadleaf weeds, kochia and pigweed, equal to or better than a standard treatment of pendimethalin. Flumioxazin and sulfentrazone controlled prickly lettuce, marestail, and common groundsel well when split applied to dormant mint in the fall and spring. MCPB applied twice at 0.25 lb ae/a to Scotch spearmint infested with field bindweed increased oil yield of mint compared to nontreated checks. Western salisfy often escapes control by herbicides in mint fields but was controlled with clopyralid oxyfluorfen, terbacil, flumioxazin and sulfentrazone when applied at specific growth stages in greenhouse tests. Western salsify was susceptible to all five herbicides at the one leaf stage of growth.

Technical Abstract: The presence of weeds reduces the quality and quantity of mint oil produced and weed management is important to mint producers. The goal of this research is to develop improved weed control methods in spearmint and peppermint and to identify promising new herbicides on spearmint and peppermint. Flufenacet applied preemerngece caused minor injury to spearmint and was least injurious of four herbicides tested in native spearmint. Clomazone and sulfentrazone controlled kochia and redroot pigweed equal to or better than pendimethalin in peppermint. Pendimethalin, flumioxazin, and sulfentrazone applied in fall, spring dormant, and after first cutting caused only minor injury to spearmint and peppermint and controlled weeds to varying degrees. Split applications of sulfentrazone improved prickly lettuce control and split applications of flumioxazin improved marestail control. A split application of flumioxazin or sulfentrazone in fall and spring resulted in the greatest spearmint yield of spearmint oil. MCPB suppressed field bindweed well when applied twice at either 0.25 or 0.5 lb ai/a. MCPB at 0.25 lb ae/a increased oil yield of Scotch spearmint (2nd cutting) compared to untreated field bindweed infested checks or spearmint treated with 0.5 lb ae/a MCPB or 2,4DB ester at 0.5 lb ae/a. Salsify emergence from planted seed peaked 1 to 2 months after planting in October or July and very few seed were viable after six to twelve months in the soil. Salsify was susceptible to several herbicides applied in the preemergence up to the 4-lf stage of growth, including sulfentrazone, oxyfluorfen, clopyralid, and flumioxazin.