Submitted to: Proceedings Mint Industry Research Council
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2000
Publication Date: 1/1/2001
Citation: BOYDSTON, R.A., BAKER, R., BIRCH, L.M. WEED RESEARCH IN MINT IN WASHINGTON STATE. PROCEEDINGS MINT INDUSTRY RESEARCH COUNCIL, LAS VEGAS, NV. JAN 2001. Interpretive Summary: Peppermint and spearmint are oil crops that are important to the economy of the Pacific Northwest. Weeds infest mint fields and cause oil yield loss and reduce the quality of mint oil. Mint is grown without tillage to reduce the spread of Verticillium in fields. Thus most weed control in mint is accomplished with herbicides and crop rotation. Herbicide resistant weeds and certain weed species are becoming more difficult to control in mint with currently registered herbicides. Research by ARS scientists has identified herbicides that selectively control several weed species that are not currently controlled well with herbicides labeled for use in mint. Fluroxypyr and pyrithiobac are two herbicides found to be selective in mint and both suppress field bindweed. Several other herbicides were identified that will aide growers in preventing herbicide resistant weed populations from developing since their mode of action is unlike that of currently labeled mint herbicides. IR-4 trials were initiated with flumioxazin and sulfentrazpne to collect residue data needed for registration of these herbicides in spearmint and peppermint.
Technical Abstract: Weeds cause oil yield loss and reduce the quality of mint oil. Weed control is a primary concern of mint producers. Sulfentrazone and clomazone herbicide combinations applied preemergence were safe on native spearmint. Fluroxypyr at 0.25 and 0.38 lb ai/acre applied at three growth stages of native spearmint caused excessive crop injury, but when applied at lower rates, spearmint recovered. Fluthiamide and azafenidin applied preemergenc to native spearmint caused excessive crop injury, but flumioxazin did not. Paraquat applied in March to 770 Scotch spearmint controlled common groundsel both alone and in combination with pendimethalin or terbacil. A new formulation of pendimethalin (3.8 lb ai/gal) injured 770 Scotch spearmint less than the Prowl 3.3 lb ai/gal formulation. Injury increased with increasing pendimethalin rate and when applied later in the spring to emerged spearmint. Sulfentrazone and two formulations of pendimethalin applied preemergence to newly planted peppermint controlled annual weeds well with minimal crop injury. Sulfentrazone also suppressed yellow nutsedge. Bentazon and pyridate applied postemergence to newly planted peppermint controlled small pigweed and common lambsquarters equal to bromoxynil while injuring peppermint less than bromoxynil. Pyrithiobac applied postemergence to native spearmint and peppermint suppressed field bindweed without severely stunting the mint. IR-4 residue studies were completed with sulfentrazone at three locations to establish a tolerance for this herbicide in spearmint and peppermint.