Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Schmid S., Turnage G., Ervin G.

Alligator weed (Alternanthera philoxeroides) was first introduced into the United States in 1897 from Argentina and has since become a widespread invasive species that threatens global water resources. In infested systems, alligator weed can form dense mats that displace native plants and interfere with natural ecosystem processes. Alligator weed has been a persistent problem in Mississippi and is the most commonly surveyed aquatic plant in the state. Foliar herbicide applications are commonplace for reducing alligator weed biomass, and although the plant has shown high susceptibility to these methods, its extensive stolon network facilitates robust and rapid regrowth. However, many herbicides labeled for use in aquatics can be applied directly to the water column as a submersed injection; this method allows herbicides to be taken up by roots rather than foliage and may provide more efficacious biomass reduction than foliar herbicide applications. For this study, we compared the efficacy of five herbicides (bispyribac-sodium, fluridone, imazamox, penoxsulam, and topramezone) applied as submersed injections at maximum and half-maximum label rates to reduce alligator weed grown in outdoor and greenhouse mesocosms. Our results identify multiple highly successful control methods to be tested on field populations of alligator weed and tested as part of an integrated control strategy. Aside from chemical control, the alligator weed flea beetle (Agasicles hygrophila) has been used as a biocontrol agent in the U.S. but it is very intolerant to cold climates. Therefore, a secondary biocontrol agent, the alligator weed thrips (Amynothrips andersoni), may be of use as part of an integrated control strategy as it is more cold tolerant. However, research on the thrips is diminutive compared to the flea beetle. Our future work will assess these chemical control strategies integrated with alligator weed thrips with a goal of developing an effective integrated pest management plan for alligator weed in Mississippi.