Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Turnage G., Wersal R., Madsen J.

Torpedograss (Panicum repens) is a perennial invasive aquatic plant species native to South America that is spreading across the southeastern US. Torpedogass can survive in terrestrial and aquatic environments rooted to hydrosoil or form large floating islands (tussocks) that can limit human and wildlife uses of waterbodies. Portions of tussocks can break off, float away, and start new torpedograss infestations in other locations thereby making the problem worse. Limited data exist concerning submersed chemical control (herbicides) methods that are effective at controlling torpedograss. This work was conducted to investigate short- and long-term submersed chemical control options of torpedograss grown in outdoor mesocosms near Starkville, MS. Nine herbicides labeled for use in aquatic environments and a non-treated reference were evaluated. Eight weeks after treatment (WAT), harvested plants were separated into root/rhizome and shoot/leaf tissues, placed in labeled paper bags, dried in a forced air oven for five days at 70C, then weighed. None of the herbicides significantly reduced root/rhizome tissues for torpedograss eight WAT, however penoxsulam, topramezone, flumioxazin, and carfentrazone-ethyl had reduced root/rhizome tissue by 52 WAT (57%, 64%, 97%, and 62% reduction, respectively). Triclopyr, diquat, flumioxazin, and carfentrazone-ethyl had reduced shoot/leaf tissue at eight WAT (57%, 47%, 98%, and 49% reduction, respectively). At 52 WAT, penoxsulam, topramezone, flumioxazin, and carfentrazone-ethyl had reduced shoot/leaf tissues by 49%, 66%, 97%, and 57%, respectively. While no herbicide treatment reduced root/rhizome biomass below pre-treatment levels, flumioxazin did reduce shoot/leaf tissues below pre-treatment levels. This work suggests that submersed applications of penoxsulam, topramezone, flumioxazin, or carfentrazone-ethyl can provide long-term control of torpedograss populations.