Submersed Herbicides and Thrips Biological Control Effectively Reduce Biomass of Alligatorweed (Alternanthera Philoxeroides), a Widespread Aquatic Invasive Plant

Schmid, S. A., Turnage, G., & Ervin, G. N. (2024). Submersed Herbicides and Thrips Biological Control Effectively Reduce Biomass of Alligatorweed (Alternanthera Philoxeroides), a Widespread Aquatic Invasive Plant. BioControl. 69(4), 471-481. DOI:10.1007/s10526-024-10262-5.

Alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.; Amaranthaceae] is a globally problematic, aquatic invasive weed with a long history as a target for control efforts. Although chemical and biological control methods have been widely studied to manage alligatorweed infestations, many research questions remain unanswered. This paper seeks to assess the efficacy of two understudied alligatorweed control methods: submersed herbicide applications and biological control with alligatorweed thrips (Amynothrips andersoni O'Neill 1968; Thysanoptera: Phlaeothripidae). These assessments were carried out in mesocosm experiments, in two stages. The first stage tested five herbicides applied as submersed injections at two different rates, and the second tested the same five herbicides alone and in combination with alligatorweed thrips biological control. The submersed herbicides used in this study were penoxsulam, bispyribac-sodium, imazamox, fluridone, and topramezone. The control effect of these treatments was measured as percent biomass reduction 12 weeks after treatment. These data showed that, with the exception of bispyribac-sodium, submersed herbicide application was generally successful at reducing alligatorweed biomass. Also, thrips biological control was broadly effective at reducing alligatorweed biomass. However, these data did not identify a specific herbicide whose control was significantly benefitted by thrips biological control at the rates these herbicides were applied. While the results of this study show promise for combining submersed herbicides and alligatorweed thrips for integrated alligatorweed management, questions remain regarding this combined control strategy including whether or not these results translate to the field.