Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Ervin G.N., Turnage G., Calhoun K.

Resource managers of public lands, such as national wildlife refuges, manage their lands not only for the resident fish and wildlife species, but also for patrons who utilize those resource areas. Occasionally, the dominance of problematic native plant species interferes with the intended uses of these areas. One example of this is when dense growth of aquatic vegetation blocks access to or effective use of waterbodies. In Mississippi and adjacent states, native plant species, such as Nelumbo lutea or Limnobium spongia, sometimes reach nuisance levels; however, few methods are currently known that allow the control of problematic native plant species such as these.

Our work is aimed at evaluating several chemicals for their potential to manage these plants in a way that mitigates their negative impacts on recreational use, while also minimizing potential negative impacts on water quality and desirable native plant species. We are conducting mesocosm studies to evaluate six systemic herbicides and one contact herbicide (at two dosage levels each) for their potential to control four target plant species (the above-mentioned two plus Nymphaea odorata and Brasenia schreberi).

During the first 3 weeks after treatment (WAT), we observed rapid response to some of the herbicides and dosages being evaluated. At that point, all three modes of action included in the study had shown at least 50 percent mortality on all four of the species included in the study, with only two chemical species combinations not reaching 50 percent mortality within 3 weeks. In fact, 2,4-D, Glyphosate, Triclopyr, and Flumioxazin all caused 50 percent mortality of three of the species during the first week, with other chemicals causing 50 percent mortality of the fourth species within the first WAT. At 8 WAT, we still saw continued control of all species except fragrant water lily, based solely on leaf count data. Additionally, we found that, although some herbicides caused a pulse of nitrate concentrations at 4 weeks after achieving 50% mortality, those nutrient concentrations recovered to levels comparable to untreated tanks over the ensuing 4 weeks. We did not find any other evidence of potential negative impacts on water quality in any of the treatments.