Chemical control of the floating aquatic plants common duckweed (Lemna minor L.) and watermeal (Wolffia spp.)

Author(s): Turnage, G.

Floating plants are increasingly becoming widespread problems in waterways in the southern United States. Nuisance problems are often exacerbated with increased nutrient inputs into waterbodies from point and non-point sources. Common duckweed (Lemna minor L.) and watermeal (Wolffia spp.) are both floating aquatic plant species that can be problematic in southeastern waterbodies. Infestations of these species can reduce the use and aesthetics of waterbodies and can shade out submersed aquatic plants potentially causing oxygen depletions in which may result in fish kills. Duckweed and watermeal are some of the most difficult aquatic species to control due to their high rate of reproduction. Most management options utilizing chemical control methods produce inconsistent results when used on these species. This work analyzed the effects of the contact herbicide diquat and a new liquid formulation of the contact herbicide flumioxazin when used to control duckweed and watermeal. Each species was established in 20 40L aquaria in a greenhouse and were allowed to grow for one month prior to herbicide applications. Diquat was applied to each species at the maximum label rate while flumioxazin was applied to each species at low, medium, and high rates. All herbicides and rates reduced duckweed by four weeks after treatment (WAT) when compared to an untreated control. Diquat and the high and medium rates of flumioxazin reduced watermeal when compared to the untreated control at four WAT, however the low rate of flumioxazin did not.

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