Submitted to: Washington Mint Drops
Publication Type: Popular Publication
Publication Acceptance Date: November 3, 2003
Publication Date: December 5, 2003
Citation: BOYDSTON, R.A. WEED CONTROL IN MINT - TWO NEW PRODUCTS SOON TO BE AVAILABLE. WASHINGTON MINT DROPS, P. 3. FALL 2003. Interpretive Summary: Producers of peppermint and spearmint must control weeds to prevent losses in oil quality and quantity. Two new herbicides have been tested and will soon be labeled for use in peppermint and spearmint production. Clomazone is a chlorophyll pigment inhibitor, and turns susceptible emerging weeds white. Sulfentrazone targets cell membranes and susceptible weeds emerge and die shortly thereafter. Both herbicides should be applied prior to mint and weed emergence in the spring. Clomazone primarily control annual grass weed species including barnyardgrass, crabgrass, and green foxtail. Sulfentrazone primarily controls broadleaf weed species including kochia, lambsquarters, Russian thistle, common groundsel, and nightshade species. Since the two herbicides control a somewhat different spectrum of weeds they make excellent tank mix partners for broad spectrum weed control in mint. If winter annual weeds are present at the time of application, paraquat should be tank mixed with clomazone and sulfentrazone to control emerged weeds. These two herbicides being a different mode of action than most currently labeled mint herbicides, can be used in rotation other herbicides differing in mode of action to help prevent herbicide resistant weeds from developing in mint rotations.
Technical Abstract: Weeds in spearmint and peppermint lower oil yield and quality. Two new herbicides will be available for growers for use in peppermint and spearmint production in the spring of 2004. Both herbicides should be used only on dormant mint prior to the emergence of weeds. Clomazone, a photosynthesis pigment inhibitor, controls many annual grass and broadleaf weeds, which emerge white and die after several days. Clomazone use rates will be between 0.25 to 0.5 lb ai/a in mint. Clomazone is primarily a grass herbicide, but also has activity on some broadleaf weeds, including common lambsquarters, kochia, and smartweed. Annual grass weeds that clomazone controls are barnyard grass, crabgrass, and green foxtail. Clomazone can persist enough to injure wheat planted in the fall after a spring application. Potato, field corn and sweet corn can be planted 9 months after clomazone application while 12 months is recommended before planting wheat, and 16 months before planting onions. If winter annual weeds are present at the time of application, paraquat should be tank mixed with clomazone for control. Sulfentrazone is primarily a broadleaf herbicide and it particularly strong on pigweed and nightshade species and also suppresses yellow nutsedge well. Several other key weeds that sulfentrazone controls are Russian thistle, kochia, smartweed, and common groundsel. Sulfentrazone mode of action is similar to that of oxyfluorfen, and it controls weeds by inhibiting an enzyme involved in chlorophyll synthesis, ultimately destroying cell membranes. Being a different mode of action than terbacil, sulfentrazone will control terbacil resistant pigweed and lambsquarters biotypes. Sulfentrazone use rates will depend on soil texture, organic matter, and soil pH so adjust rates to soil descriptions on the label. For most Washington soils, rates will range from 0.094 to 0.25 lb ai/a. Sulfentrazone is moderately persistent in the soil and can injure sensitive crops, such as sugarbeets if planted within 24 months after application. Plant back restrictions for sweet corn is 18 months, field corn 10 months, and wheat 4 months.