Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Turnage G., Thompson W.

Alligatorweed (Alternanthera philoxeroides) is the most widespread aquatic weed in Mississippi. Alligatorweed is capable of growing in aquatic, wetland, and terrestrial sites and switches growth form from a rhizomatous mat forming plant (aquatic) to a prostrate growth form with tap roots (terrestrial) which allows it to survive stressors such as drawdown or drought. Much is known regarding the impacts and control of alligatorweed in aquatic sites, however, less is known regarding control of alligatorweed in terrestrial sites. Muscadine Farms Wildlife Management Area (WMA) is a series of 90 ponds (each 6.1-8.1 hectares in size) that covers approximately 809 ha in the Mississippi flyway in western Mississippi; the WMA is primarily managed for waterfowl habitat. The terrestrial form of alligatorweed has infested many ponds in the WMA and displaced desirable vegetation utilized as waterfowl forage. In 2022, an herbicide trial was conducted and repeated two weeks later to assess the reduction of alligatorweed at Muscadine Farms by herbicides utilized for operational control of alligatorweed as well as newer herbicides labeled for use in aquatics in the last two decades. Herbicides were applied to 83.6 m-2 (9.1 by 9.1 m) plots at Muscadine Farms. High and low rates of imazapyr (8.2 and 4.1 kg a.e. ha-1), bispyribac-sodium (0.11 and 0.055 kg a.i. ha-1), topramezone (11.4 and 5.7 kg a.e. ha-1), florpyrauxifen-benzyl (0.02 and 0.01 kg a.i. ha-1), and fluridone (10.9 and 5.4 kg a.i./ha-1) were tested as stand-alone foliar herbicide treatments. Glyphosate (11.0 kg a.i. ha-1), triclopyr (11.7 kg a.e. ha-1), metsulfuron-methyl (0.036 kg a.i. ha-1), and two-way tank mixes of the three were also tested as foliar treatments. All herbicide applications included a 0.5% v:v MSO surfactant and were applied at a 467.7 L ha-1 (50 gal ac-1) diluent rate. Each treatment was replicated four times. This is the first report of alligatorweed control by bispyribac-sodium (88 to 94% reduction), topramezone (76% reduction), florpyrauxifen-benzyl (85% reduction), or fluridone (76 to 93% reduction) suggesting that these herbicides may provide another alligatorweed control option for resource managers. A follow up trial found that disking or mowing alone provided 99 and 72% reduction (respectively) of alligatorweed biomass suggesting these may be suitable non-chemical control techniques for alligatorweed in terrestrial systems.