Proceedings of the 2020 Mississippi Water Resources Conference

Year: 2020 Authors: Lazaro-Lobo A., Turnage G., Ervin G.N.

Limnobium spongia is a free-floating aquatic plant that can produce extensive floating mats and can cause negative ecological, social, and economic impacts. Literature describing effective control measures for L. spongia and possible changes in water quality following herbicide treatment of aquatic plants is minimal. We conducted a mesocosm study to assess the effect of seven herbicides at low and high doses in an effort to control L. spongia while minimizing negative impacts on water quality attributes. We found that low and high doses of imazamox, imazapyr, and flumioxazin herbicides effectively controlled L. spongia initially and during the next growing season, whereas 2,4-D at both rates, as well as high doses of glyphosate and triclopyr initially controlled the species but failed to contain the regrowth of the species during the next summer. Low doses of glyphosate and triclopyr gave poor control of L. spongia, and none of the florpyrauxifen-benzyl rates had any effect on the plants. Furthermore, we found that the increment in light availability after the herbicide-induced death of L. spongia promoted the growth of algae and other photosynthetic organisms in the mesocosms. This led to an increase in dissolved oxygen availability and water column pH. Decreases in plant cover in the mesocosms was correlated with increased electrical conductivity and nitrate concentrations during the first 4 months of the experiment, which potentially could lead to eutrophication issues during plant control efforts at a larger scale, without adequately short residence times in treated water bodies.