Evaluation of foliar herbicide and surfactant combinations for control of giant salvinia at three application timings

摘要

The invasive aquatic fern, giant salvinia (Salvinia molesta Mitchell) continues to spread throughout Louisiana, Texas, and the Gulf Coast Region. Most infestations in Louisiana are chemically managed throughout the growing season with a combination ofthe aquatic herbicides glyphosate and diquat plus two adjuvants (nonionic surfactant with buffering agents and a nonionic organosilicone surfactant). Heavy reliance on one spray mixture is of concern to natural resource managers because of the possibility of developing herbicide resistance. In addition, it is unknown whether combinations of other herbicides and adjuvants or surfactants can provide improved efficacy at certain times of the year (i.e., seasonal differences) compared with the primary treatment used operationally. Therefore, three mesocosm trials were conducted in the spring, summer, and fall to evaluate the efficacy of various combinations of glyphosate, carfentrazone-ethyl (hereafter, called carfentra-zone), diquat, endothall, flumioxazin, and adjuvants on giant salvinia. All treatments involving glyphosate + carfentra-zone or flumioxazin, as well as endothall + flumioxazin, resulted in giant salvinia injury 1 d after treatment. Glyphosate alone required 4 d to produce injury symptoms.All treatments, regardless of application time, were efficacious against giant salvinia 7 wk after treatment and reduced plant dry weight by 65 to 99% compared with the nontreated control. In general, fall herbicide treatments were less efficacious thanthe spring or summer treatments, and a great amount of regrowth also occurred following this application. The substitution of carfentrazone or flumioxazin for diquat into the glyphosate spray mixture, as well as other surfactants or adjuvants, providedsimilar control to the herbicide mixture used operationally in Louisiana. Based on these data, the new mixtures evaluated in the spring and summer can be viable alternatives to manage salvinia during the growing season. Further research is needed to evaluate other mixes for the fall when plant growth is decreasing.