J. Aquat. Plant Manage. 56: 107–112 Evaluation of 12 foliar applied non-aquatic herbicides for efficacy against giant salvinia (Salvinia molesta) BRADLEY T. SARTAIN AND CHRISTOPHER R. MUDGE* ABSTRACT al. 1990), Australia (Forno and Harley 1979), and the United States (Johnson 1995). The first reported documentation of Registered aquatic herbicides are frequently used for giant salvinia established in the United States occurred in managing the invasive aquatic fern giant salvinia (Salvinia 1995 in South Carolina (Johnson 1995). Since 1995, it has molesta D.S. Mitchell). Unfortunately, there is a limited been found in an additional 11 states including Alabama, number of efficacious and economically feasible products Arizona, California, Florida, Georgia, Hawaii, Louisiana, available for large-scale management. Therefore, outdoor Mississippi, North Carolina, Texas, and Virginia (Thayer et mesocosm trials were conducted to evaluate nonaquatic al. 2018). registered herbicides for efficacy against giant salvinia. In Giant salvinia exhibits very rapid growth, with plant the first trial, metsulfuron and sulfometuron were the most biomass doubling under greenhouse conditions in only 2.2 d effective. Both treatments caused plants to become necrotic, (Cary and Weerts 1983). Conversely, field observations have lose buoyancy, and desiccate as early as 2 wk after treatment shown the amount of time for a twofold increase in plant (WAT) and 100% plant mortality was documented by 8 biomass to range from 1 to 8 d (Finlayson 1984, Room 1986). WAT. In addition, clomazone, halosulfuron, and bensulfur- In addition, it forms dense mats made of multiple plant on provided 69, 76, and 77% control, respectively. Herbi- layers that have been documented up to 1 m thick cide treatments that provided 30% control in Trial 1 (McFarland et al. 2004). Dense plant growth impedes (with the exception of clomazone) were re-evaluated in Trial navigation, irrigation, and recreational use of infested water 2 at additional rates. All herbicide treatments in Trial 2 bodies (Pimentel et al. 1999), leading to not only environ- significantly reduced giant salvinia biomass compared with mental impacts, but economic impacts and public health the nontreated reference. In addition, all three rates of concerns (McFarland et al. 2004). These negative impacts metsulfuron and sulfometuron provided 98 to 99% control. have led to situations where giant salvinia needs to be Although sulfometuron and metsulfuron did not provide intensively managed to limit its growth and spread to 100% giant salvinia control in Trial 2 at 12 WAT, no new surrounding water bodies. frond growth was observed and harvested material consisted Small-scale research and large-scale field operations have of small rhizome fragments that had little to no viability. shown that aquatic herbicides are capable of managing The results of these studies conclude that giant salvinia is giant salvinia infestations in the United States (McFarland et sensitive to low use rates of metsulfuron (21 g ai haÀ1) and al. 2004). Currently, 14 active ingredients are registered by sulfometuron (158 g ai haÀ1) and regrowth of treated plant the U.S. Environmental Protection Agency (USEPA) for use material is minimal. in or around aquatic sites; however, only 10 have activity on Key words: Louisiana, management, mesocosm, metsul- giant salvinia (Table 1) (Nelson et al. 2001, Glomski et al. furon, sulfometuron, Texas. 2003, Glomski and Getsinger 2006, Mudge and Harms 2012, Mudge et al. 2012, 2013, Glomski and Mudge 2013, Mudge INTRODUCTION 2016). To date, glyphosate and diquat applications are the most effective for giant salvinia control (Mudge et al. 2016), Giant salvinia (Salvinia molesta D.S. Mitchell) is a free- but other herbicides including carfentrazone-ethyl, flu- floating aquatic fern that originates from Brazil (Jacono mioxazin, bispyribac-sodium, penoxsulam, and toprame- 1999, Jacono and Pitman 2001, McFarland et al. 2004). Over zone have demonstrated varying levels of control when the past 80 yr, giant salvinia has spread outside of its native applied alone or in combination with other chemistries range in South America (Oliver 1993, Jacono and Pitman (Glomski and Getsinger 2006, Mudge and Harms 2012, 2001) to Africa (Mitchell and Tur 1975, Cilliers 1991), India Mudge et al. 2012, Glomski and Mudge 2013, Mudge 2016, (Cook 1976), Sri Lanka (Room 1990), Southeast Asia (Baki et Mudge et al. 2016). A combination of glyphosate (3.4 kg ae haÀ1), diquat (0.5 À1 First author: Graduate Research Assistant, Louisiana State University kg ai ha ), and two surfactants has been used almost School of Plant Environmental and Soil Sciences, Baton Rouge, LA exclusively for giant salvinia control by the Louisiana 70803. Second author: Research Biologist, U.S. Army Engineer Research Department of Wildlife and Fisheries (Mudge et al. 2016) and Development Center, Louisiana State University School of Plant Environmental and Soil Sciences, Baton Rouge, LA 70803. Correspond- as well as other federal and state agencies in Louisiana and ing author’s E-mail: [email protected]. Received for Texas. Despite this combination being effective against publication March 5, 2018 and in revised form April 9, 2018. giant salvinia, the continuous use of one herbicide or one J. Aquat. Plant Manage. 56: 2018 107 À1 TABLE 1. REGISTERED AQUATIC HERBICIDES THAT ARE EFFICACIOUS ON GIANT SALVINIA. TABLE 2. HERBICIDE RATES (GAIHA ) APPLIED TO THE FOLIAGE OF GIANT SALVINIA 1 AND THE NUMBER OF WEEKS UNTIL PLANTS DOCUMENTED 25% VISUAL INJURY IN Herbicide Mode of Action Application Method HERBICIDE SCREENING TRIAL 1. Bispyribac-sodium ALS inhibitor Foliar/subsurface Rate1 25% Visual Injury Carfentrazone-ethyl PPO inhibitor Foliar/subsurface À1 Herbicide Treatments gaiha WAT Copper Not classified Foliar/subsurface Diquat Photosystem I inhibitor Foliar/subsurface Bensulfuron 70 2 Endothall Not classified Foliar/subsurface Clomazone 1,393 2 Flumioxazin PPO inhibitor Foliar/subsurface Flumiclorac 60 1 Fluridone Carotenoid biosynthesis Subsurface Glufosinate 882 1 inhibitor Halosulfuron 290 2 Glyphosate EPSP synthase inhibitor Foliar Metsulfuron 42 2 Penoxsulam ALS inhibitor Foliar/subsurface Florpyrauxifen-benzyl 117 N/A Topramezone Carotenoid biosynthesis Foliar Rimsulfuron 35 N/A inhibitor Saflufenacil 150 1 1Abbreviations: ALS ¼ acetolactate synthase, PPO ¼ protoporphyrinogen oxidase, Sethoxydim 526 N/A EPSP ¼ enolpyruvyl shikimate-3-phosphate. Sulfometuron 315 2 Trifloxysulfuron 21 3 1 spray mixture will be detrimental if giant salvinia were to Abbreviations: WAT ¼ weeks after treatment, N/A ¼ not applicable; indicates that plant injury never exceeded 25%. develop resistance to either herbicide in the future (Mudge et al. 2016). Although herbicide resistance in aquatic weed management has been limited to fluridone-resistant hydrilla additional rates. Giant salvinia used in this research was (Hydrilla verticillata L.f. Royle) (Michel et al. 2004) and diquat- collected from cultures maintained at LSU Aquaculture. resistant landoltia duckweed [Landoltia punctata (G. Meyer) In both trials, plants were cultured in 76-L plastic D.H. Les and D.J. Crawford] (Koschnick et al. 2006), over 250 containers (49.5 cm diam by 58.4 cm height) filled with 60 herbicide-resistant plant species have been documented L of pond water (pH 8.5). Before planting, pond water was amended with sphagnum peat moss (14 g) to lower the pH to globally at a rate of 11 new cases per year (Heap 2014, Heap , 7.0. Equal amounts of fresh plant material, enough to 2017). Best management practices that promote the cover approximately 85% of the water surface, were placed rotation of herbicides are encouraged to decrease the in each 76-L container. In addition, 2.1 g of Miracle-Grot1 chances of establishing resistant plant populations. As a water-soluble lawn food (24–8–16) was applied to each result of the overuse of two active ingredients and a limited container at planting and every 2 wk throughout both trials number of efficacious aquatic herbicides, it is important to to encourage plant growth. Plants were allowed to acclimate evaluate other potential chemistries (i.e., herbicides with to container conditions for 2 wk before herbicide applica- different modes of action) and/or nonaquatic herbicides. tion. At herbicide application, plants had reached ca. 100% Herbicide screenings for giant salvinia have been limited coverage, with mean dry weights of 33.76 6 1.59 and 28.72 because it is considered a regional weed compared with 6 2.03 g for trials 1 and 2, respectively. Culture and more widespread invasive aquatic species such as hydrilla planting techniques were adapted from previous giant and Eurasian watermilfoil (Myriophyllum spicatum L.). Re- salvinia research (Nelson et al. 2007, Mudge et al. 2012, gional weed problems represent a small market for the Mudge et al. 2016). herbicide industry and essentially it is not economically Herbicides evaluated during trials 1 and 2 included beneficial to develop new chemistries for a regional weed acetolactate synthesis inhibitors (ALS): bensulfuron,2 hal- species. Products including bispyribac, carfentrazone, flu- osulfuron,3 metsulfuron,4 rimsulfuron,5 sulfometuron,6 tri- mioxazin, imazamox, penoxsulam, and topramezone were floxysulfuron;7 protoporphyrinogen oxidase inhibitors screened, developed, and registered for aquatic use after (PPO): saflufenacil8 and flumiclorac;9 carotenoid biosynthe- fluridone-resistant hydrilla was discovered in the late 1990s sis