Submitted to: Washington Mint Drops
Publication Type: Popular Publication
Publication Acceptance Date: 10/22/2004
Publication Date: 11/8/2004
Citation: Boydston, R.A. 2004. Postemergence broadleaf weed control with low rates of spartan and callisto in mint. Washington Mint Drops. Washington Mint Growers Association. Fall issue:2-5. Interpretive Summary: Controlling broadleaf weeds in mint after the weeds and mint have emerged has always been a challenge. Growers must weigh the risk of herbicide damage to the mint against the risk of leaving uncontrolled weeds to compete with mint. Weeds resistant or tolerant to herbicides currently labeled in mint are becoming prevalent in mint growing regions. This research evaluated low rates of sulfentrazone and mesotrione herbicides for postemergence control of broadleaf weeds in mint when applied alone and in tank mixes with other herbicides labeled in mint. Low doses of sulfentrazone and mesotrione initially injured both peppermint and spearmint, but mint regrew normally and yielded more oil than in plots where weeds were not controlled. Tank mixes of bentazon with sulfentrazone reduced injury to the mint. Tank mixes of bromoxynil with mesotrione greatly increased injury to the mint. These two herbicides could be useful in managing broadleaf weeds that currently are tolerant or resistant to currently labeled herbicides used in mint.
Technical Abstract: Postemergence broadleaf weed control with herbicides is difficult in peppermint and spearmint due to a narrow margin of herbicide selectivity between mint and broadleaf weeds. Research was conducted to evaluate mint tolerance to two postemergence applied herbicides, sulfentrazone and mesotrione, applied at low doses alone and in various tank mixes. Initial native spearmint injury after treating with sulfentrazone alone or in tank mixes ranged from 4 to 39%, but both peppermint and native spearmint recovered several weeks after application. Bentazon applied with sulfentrazone acted as a safener, reducing the mint injury. Pigweed control with low dose tank mixes of sulfentrazone was similar to that obtained with pyridate. Oil yield of native spearmint treated with sulfentrazone at 0.016 lb ai/a alone or in tank mixes was not reduced compared to mint treated with pyridate and tended to be greater than oil yield in plots where pigweed was not controlled. Mesotrione applied at 0.032 lb ai/a alone and in tank mixes initially injured mint from 25 to 70%, but both peppermint and native spearmint recovered several weeks after application. Greatest mint injury occurred in tank mixes with bromoxynil. Pigweed control with mesotrione alone or in tank mixes ranged from 98 to 100%. Oil yield of native spearmint treated with mesotrione tank mixes with bentazon or terbacil was greater than oil yield in plots where pigweed was not controlled. Given the excellent pigweed control observed in these two trials, the two herbicides have potential to be used in mint at low rates without sacrificing mint oil yield.