Florpyrauxifen-benzyl (aquatic tradename ProcellaCOR) is an aquatic herbicide commonly used to control Eurasian watermilfoil (Myriophyllum spicatum) and other invasive aquatic plants. Previous studies have demonstrated effective Eurasian watermilfoil control under low aqueous concentrations (<10 µg L−1) and short exposure times (< 24 hr). Although florpyrauxifen-benzyl possesses an excellent environmental profile and its acute toxicity has been assessed in freshwater model organisms, there has been no work to examine toxicity of this herbicide in salmonids. Therefore, the objective of this study was to evaluate the acute toxicity to Endangered Species Act-listed Chinook salmon (Oncorhynchis tshawytscha). Chinook fry and smolts were exposed to florpyrauxifen-benzyl at 50 and 100 µg L−1 for 96 hr under a 24-hr static renewal protocol at 12 °C. Daily observations included fish startle response, position in the water column, and signs of overt toxicity. No adverse effects of the herbicide were observed at either concentration in both Chinook fry and smolts. Our results indicate that the maximum United States-labeled application rate of florpyrauxifen-benzyl (48 µg L−1 ai) did not result in overt toxicity to juvenile salmonids under the exposure scenarios used in this study.

A series of 10 water-exchange studies were conducted from 2019 to 2021 at two sites, Clover Island and Osprey Point, within the McNary Pool of the Columbia River on the Oregon-Washington border. Six of the studies incorporated a barrier curtain or bubble curtain, whereas the other four studies did not include any device to mitigate water exchange. Once annually, diquat aquatic herbicide was applied concurrently with rhodamine water tracing (RWT) dye at the Osprey Point site (2019–2021) to control flowering rush. An additional plot, Clover Island Reference, served as the nontreated control to the Osprey Point treatment plot. Pre- and posttreatment vegetation surveys were conducted in 2019, 2020, and 2021 to determine flowering rush control, treatment impacts to water quality, and nontarget species response. This study sought to (1) document the use of barrier curtains and bubble curtains as potential methods for reducing water exchange and increasing herbicide concentration exposure times within potential flowering rush treatment areas, (2) evaluate bulk water exchange and selective control of flowering rush under varying reservoir operations, and (3) use the results from these studies to provide guidance for managing submersed flowering rush infestations on the McNary Pool, Columbia River, and similar run-of-the-river impoundments.

Mesocosm experiments were conducted in 2020 and 2021 in Louisiana and Florida to evaluate the effects of foliar spray application factors on spray deposition patterns for applications to floating aquatic plants using tracer dye. In the first experiment, spray trajectory and associated impact angles were investigated. A forward spray trajectory angle of 90 degrees decreased spray loss by 22% to the water column when targeting waterhyacinth [ Eichhornia crassipes (Mart.) Solms], compared to downward 90 degrees and forward 45 degrees spray angles. However, no difference in spray loss was detected for waterlettuce ( Pistia stratiotes L.) among tested spray trajectory angles. The second experiment tested spray pattern (single-nozzle cone via spray-gun, single-nozzle straight stream via spray-gun, and multinozzle broadcast boom) effects on spray loss for applications to waterhyacinth, water lettuce, and giant salvinia ( Salvinia molesta D.S. Mitchell). For waterhyacinth, spray loss was greatest with single-nozzle cone (51%), followed by single- nozzle straight stream (34%), followed by broadcast boom (25%). However, spray loss for waterlettuce was greatest using single-nozzle straight-stream applications (61%) and lowest with broadcast boom (40%) and single-nozzle cone (35%) applications. Spray loss for giant salvinia was greatest for single-nozzle cone applications (32%) and least for broadcast boom applications (19%). A third experiment tested spray loss between broadcast boom and spray-to-wet spray-gun application techniques; no differences were observed between techniques in applications to waterhyacinth or waterlettuce. These results suggest that foliar spray loss when targeting common floating aquatic plants can be minimized by manipulating application parameters and likely requires species-specific considerations. These results require verification under operational field conditions to develop best management practices to reduce spray loss for foliar-applied aquatic herbicide applications.

The inert fluorescent dye rhodamine water tracer (RWT) has been widely used in freshwater aquatic systems for many years to quantify bulk water exchange patterns and as a tracer for submersed herbicide movement. The dye is well-suited for tracer work due to its high solubility and detectability in water (<0.01 μg/L). Federal guidelines limit the aqueous concentration 0f RWT to <10 μg/L at drinking water intakes. The dye has proven to be harmless to aquatic organisms and humans in low concentrations and is relatively inexpensive. Since 1991, RWT has been used by Engineer Re-search and Development Center (ERDC) researchers to simulate aqueous herbicide applications in large, hydrodynamic systems in over 12 states. Such simulations have improved the effectiveness of herbicide treatments by linking in situ water exchange processes with appropriate herbicide selection and application rates. Understanding these parameters can be critical for mitigating herbicide exposure in environmentally sensitive settings and around potable water and irrigation intakes. A data-based estimate of water exchange patterns usually results in successful submersed herbicide applications—both with target-plant efficacy and limited injury to nontarget vegetation. Using RWT dye to simulate submersed herbicide applications is an important predictive and real-time tool in both experimental and operational settings.

Four demonstration plots were selected at Roanoke Rapids Lake, NC to evaluate water exchange and aqueous herbicide residues in stands of submersed aquatic vegetation (SAV) following treatment with rhodamine wt dye and florpyrauxifen-benzyl to control monecious hydrilla. Florpyrauxifen-benzyl (Procellacor™ SC) was applied in combination with Rhodamine WT (RWT) at two of the plots. Dye measurements and herbicide residue samples were collected at specific time intervals to draw comparisons between herbicide and RWT dye dissipation. The two additional plots served as reference plots to the treatment plots. Pre- and post-treatment vegetation surveys were conducted to evaluate monoecious hydrilla control and non-target species response. RWT dye and herbicide residue data indicated rapid water exchange was occurring with each treatment plot. As a result, florpyrauxifen-benzyl concentration and exposure times (CETs) towards monoecious hydrilla were not sufficient to achieve adequate control by 4 weeks after treatment (WAT). To reduce the impact of hydraulic complexity and improve herbicide efficacy, treatments should coincide with minimal reservoir discharge events to extend herbicide CET relationships. Evaluations of florpyrauxifen-benzyl on late season, mature plants may have impacted herbicide efficacy. Evaluations should be conducted earlier in the growing season, on young, actively growing plants, to discern potential differences in efficacy due to treatment timing and phenology. More information on herbicide concentration and exposure time relationships for monoecious hydrilla should be developed in growth chamber and mesocosm settings to improve species selective management of monoecious hydrilla in hydrodynamic reservoirs.

Invasive emergent and floating macrophytes can have detrimental impacts on aquatic ecosystems. Management of these aquatic weeds frequently relies upon foliar application of aquatic herbicides. However, there is inherent variability of overspray (herbicide loss) for foliar applications into waters within and adjacent to the targeted treatment area. The spray retention (tracer dye captured) of four invasive broadleaf emergent species (water hyacinth, alligatorweed, creeping water primrose, and parrotfeather) and two emergent grass-like weeds (cattail and torpedograss) were evaluated. For all species, spray retention was simulated using foliar applications of rhodamine WT (RWT) dye as a herbicide surrogate under controlled mesocosm conditions. Spray retention of the broadleaf species was first evaluated using a CO2-pressurized spray chamber overtop dense vegetation growth or no plants (positive control) at a greenhouse (GH) scale. Broadleaf species and grass-like species were then evaluated in larger outdoor mesocosms (OM). These applications were made using a CO2-pressurized backpack sprayer. Evaluation metrics included species-wise canopy cover and height influence on in-water RWT concentration using image analysis and modeling techniques. Results indicated spray retention was greatest for water hyacinth (GH, 64.7 & PLUSMN; 7.4; OM, 76.1 & PLUSMN; 3.8). Spray retention values were similar among the three sprawling marginal species alligatorweed (GH, 37.5 & PLUSMN; 4.5; OM, 42 & PLUSMN; 5.7), creeping water primrose (GH, 54.9 & PLUSMN; 7.2; OM, 52.7 & PLUSMN; 5.7), and parrotfeather (GH, 48.2 & PLUSMN; 2.3; OM, 47.2 & PLUSMN; 3.5). Canopy cover and height were strongly correlated with spray retention for broadleaf species and less strongly correlated for grass-like species. Although torpedograss and cattail were similar in percent foliar coverage, they differed in percent spray retention (OM, 8.5 & PLUSMN; 2.3 and 28.9 & PLUSMN;4.1, respectively). The upright leaf architecture of the grass-like species likely influenced the lower spray retention values in comparison to the broadleaf species.

The purpose of this study was to investigate the minimum exposure time requirements for submersed treatments of diquat to effectively control flowering rush (Butomus umbellatus L.). Identifying these parameters will provide critical information for the operational management of this species in high water exchange scenarios.

Large-scale cyanobacterial harmful algal blooms (cHABs) in Lake Okeechobee, Florida, and connected waterways routinely impair water resources. This study conducted a field demonstration of a peroxide-based algaecide in 2020 in the Pahokee Marina on Lake Okeechobee to evaluate the algaecide’s suitability for near-future operational implementation. Within minutes of treatment, rapid oxidation of cHAB cells occurred in the form of bleaching and cell lysis. On average, levels in the treatment area decreased by 4 hours after treatment (HAT) and remained low out to 24 HAT: chlorophyll decreased 87%, phycocyanin decreased 85%, total microcystin levels decreased from 50 μg L−1 to 4 μg L⁻¹ at 4 HAT and then increased to 11 μg L⁻¹ by 24 HAT, hydrogen peroxide concentrations averaged 6.1 mg L⁻¹ 0.5 HAT and then dropped below detection limits by 24 HAT, and Microcystis spp. cell densities decreased at 4 HAT in all but four sampling sites. However, inflows of cHAB-infested lake water in some portions of the treatment area resulted in lack of control at these sites. Because of their vulnerability to influxes of cHABs from surrounding nontreated waters via water-exchange processes driven by wind-induced surface currents, future applications must therefore consider treatment area size.

Current dam discharge patterns in Noxon Rapids Reservoir reduce concentration and exposure times (CET) of herbicides used for aquatic plant management. Herbicide applications during periods of low dam discharge may increase herbicide CETs and improve efficacy. Applications of rhodamine WT dye were monitored under peak (736 to 765 m³ s⁻¹) and minimum (1.4 to 2.8 m³ s⁻¹) dam discharge patterns to quantify water-exchange processes. Whole-plot dye half-life under minimal discharge was 33 h, a 15-fold increase compared with the dye treatment during peak discharge. Triclopyr concentrations measured during minimum discharge within the treated plot ranged from 214 ± 25 to 1,243 ± 36 μgL⁻¹ from 0 to 48 h after treatment (HAT), respectively. Endothall concentrations measured during minimum discharge in the same plot ranged from 164 ± 78 to 2,195 ± 1,043 μgL⁻¹ from 0 to 48 HAT, respectively. Eurasian watermilfoil (Myriophyllum spicatum L.) occurrence in the treatment plot was 66%, 8%, and 14% during pretreatment, 5 wk after treatment (WAT), and 52 WAT, respectively. Myriophyllum spicatum occurrence in the nontreated plot was 68%, 71%, and 83% during pre-treatment, 5 WAT, and 52 WAT, respectively. Curlyleaf pondweed (Potamogeton crispus L.) occurrence in the treatment plot was 29%, 0%, and 97% during pretreatment, 5 WAT, and 52 WAT, respectively. Potamogeton crispus increased from 24% to 83% at 0 WAT to 52 WAT, respectively, in the nontreated plot. Native species richness declined from 3.3 species per point to 2.1 in the treatment plot in the year of treatment but returned to pretreatment numbers by 52 WAT. Native species richness did not change during the study in the nontreated reference plot. Herbicide applications during periods of low flow can increase CETs and improve control, whereas applications during times of high-water flow would shorten CETs and could result in reduced treatment efficacy.

Foliar delivery of herbicides is a common means for plant management in aquatic environments. Though this technique is decades old, little is known about vegetative spray retention relative to this application method. A more complete understanding of maximizing herbicide retention could lead to improved plant management while simultaneously decreasing pesticide load in aquatic environments. Therefore outdoor mesocosm experiments were conducted in 2020 to evaluate the effect of adjuvant type on foliar spray retention in waterhyacinth [Eichhornia crassipes (Mart.) Solms]. Additionally, the effect of carrier volume on spray retention in waterhyacinth, waterlettuce (Pistia stratiotes L.), and giant salvinia (Salvinia molesta D.S. Mitchell) was documented. Spray deposition did not differ among the nine adjuvants tested; however, spray retention was reduced 6% to 11% when an adjuvant was excluded from the spray solution. The effect of carrier volume on spray retention in waterhyacinth, waterlettuce, and giant salvinia was also investigated. Decreases in spray retention were most sensitive to increased carrier volume in waterhyacinth, followed by giant salvinia and waterlettuce. Among species, spray retention potential, as determined by intercept estimates, was greatest in waterlettuce and giant salvinia regardless of carrier volume. Asymptotes estimates for waterhyacinth, waterlettuce, and giant salvinia were 33%, 46%, and 79% spray retention, respectively. In other words, spray retention was the lowest and remained relatively constant at these values for the high carrier volumes tested (935 and 1,870 L ha-1), which were likely due to the presence of pubescence on leaves and flatter leaf architecture represented by waterlettuce and giant salvinia compared to the glabrous vertical leaves of waterhyacinth. Future research will evaluate these concepts under field conditions.

A 72 h small-scale trial was conducted in enclosed mesocosms in the Lake Okeechobee waterway to evaluate the effectiveness of a USEPA-registered peroxide-based algaecide (formulated as sodium carbonate peroxyhydrate) for controlling a natural cyanobacteria population. Mesocosms were initially subjected to either no algaecide or the maximum label rate of 10 mg H2O2·L−1. A subset of mesocosms were then subjected to a sequential application of 5 mg H2O2·L−1 at 48 h after initial treatment. Following application, peroxide concentrations rapidly decreased and were undetectable by 48 h. At 24 h after treatment, significant decreases in all biomass indicators were observed (compared to untreated mesocosms), including extracted chlorophyll a, microscopic counts (total phytoplankton and total cyanobacteria), and cyanobacteria-specific 16S rRNA gene copies by over 71%. Although peroxide treatment reduced cyanobacteria biomass, there was no change in overall community structure and the remaining population was still dominated by cyanobacteria (>90%). After 48 h exposure, some biomass recovered in single application mesocosms resulting in only a 32–45% reduction in biomass. Repeated peroxide dosing resulted in the greatest efficacy, which had a sustained (60–91%) decrease in all biomass indicators for the entire study. While a single application of the peroxide was effective in the first 24 h, a sequential treatment is likely necessary to sustain efficacy when using this approach to manage cyanobacteria in the field. Results of this study support that this peroxide-based algaecide is a strong candidate to continue with scalable field trials to assess its potential future utility for operational management programs in the Lake Okeechobee waterway.

In 2018, field trials evaluated water-exchange processes using rhodamine WT dye to provide guidance on the effective management of flowering rush (Butomus umbellatus L.) at McNary Dam and Reservoir (Wallula Lake, 15,700 ha). Additional evaluations determined the effectiveness of BubbleTubing (hereafter referred to as bubble curtain) at reducing water exchange within potential flowering rush treatment areas. Dye readings were collected from multiple sampling points at specific time intervals until a dye half-life could be determined. Whole-plot dye half-lives at sites without bubble curtain ranged 0.56–6.7 h. In slower water-exchange sites (≥2.6 h dye half-life), the herbicide diquat should have a sufficient contact time to significantly reduce flowering rush aboveground biomass. Other sites demonstrated very rapid water exchange (<1.5 h dye half-life), likely too rapid to effectively control flowering rush using chemical treatments without the use of a barrier or curtain to slow water exchange. At one site, the use of the bubble curtain increased the dye half-life from 3.8 h with no curtain to 7.6 and 7.1 h with a bubble curtain. The bubble curtain’s ability to slow water exchange will provide improved chemical control and in-crease the potential for other chemical products to be effectively used.

This study conducted small-scale trials under various concentration and exposure time (CET) scenarios to determine florpyrauxifen-benzyl activity on dioecious hydrilla and hybrid watermilfoil and determine impact on water stargrass and elodea. Hydrilla treated with 12, 24, or 36 μg active ingredient (a.i.) L⁻¹ florpyrauxifen-benzyl and exposed for 12, 24, or 48 hr under outdoor mesocosm conditions was reduced in biomass by 30-75% at 8 weeks after treatment (WAT). An additional hydrilla trial at the same herbicide concentrations, but under longer exposures (24, 72, or 168 hr), resulted in 33–85% plant control. Under indoor conditions, hybrid watermilfoil dry weight decreased 98–100% with subsurface applications of florpyrauxifen-benzyl under CET scenarios of 3–12 μg a.i. L⁻¹ at 3–24 hr exposure times in a growth chamber trial. Under shorter exposure periods (0.5–4 hr) in a follow-up trial, low doses (3–9 μg a.i. L⁻¹) achieved 50–100% control of hybrid watermilfoil. In the same trial, the nontarget species water stargrass and elodea proved relatively tolerant to the florpyrauxifen-benzyl at doses up to 6 μg a.i. L⁻¹ (4 hr exposure) and 9 μg a.i. L⁻¹ (1 hr exposure). These small-scale trials demonstrate florpyrauxifen-benzyl’s potential to selectively manage invasive species.

BACKGROUND Mesocosm experiments were conducted to evaluate the effect of floating plant density on over-the-top spray solution loss to the column using a tracer dye. Experiments quantified in-water rhodamine water tracer (RWT) dye concentration after foliar treatment at 935 L ha(-1) to waterhyacinth [Eichhornia crassipes (Mart.) Solms], waterlettuce (Pistia stratiotes L.) and giant salvinia (Salvinia molesta D.S. Mitchell) at 0, 25, 50 and 100% area covered (PAC). RESULTS As expected, spray loss to the water surface decreased with increasing plant density in all species. However, each species exhibited an unique relationship between density and percentage spray loss. The plant material required to result in 50% spray loss (ED50) was 32, 62 and 55 PAC for waterhyacinth, waterlettuce and giant salvinia, respectively. Greater ED50 estimates in waterlettuce and giant salvinia were attributed to plant architecture and leaf orientation compared to waterhyacinth, which grows more vertically and has a greater overall surface area to intercept and retain spray solution. However, when treated at 100 PAC, waterhyacinth and waterlettuce resulted in 20-25% spray loss, whereas giant salvinia resulted in only 10% loss. Consequently, giant salvinia exhibited a near 1:1 relationship between spray loss and PAC (slope = -0.93). CONCLUSION These data suggest that potential herbicide spray loss, as affected by plant density, is largely species-specific and dependent on leaf morphology and plant architecture. Further research will confirm these findings under field conditions as well as to identify other parameters that might affect spray loss when treating floating and emergent plants.

Aquatic herbicides are one of the most effective and widespread ways to manage nuisance vegetation in the US After the active ingredient is selected, often there are numerous proprietary and generic branded products to select from. To date, limited efforts have been made to compare the efficacy of brand name and generic herbicides head to head; therefore, at tot al of 20 mesocosm trials were conducted to evaluate various 2,4 -D, glyphosate, imazapyr, and triclopyr products against alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.), southern cattail (hereafter referred to as cattail, Typha domingensis Pers.), and creeping water primrose (hereafter referred as primrose, Ludwigia peploides (Kunth) P.H. Raven). All active ingredients were applied to foliage at broadcast rates commonly used in applications to public waters. Proprietary and generic 2,4 -D, glyphosate, imazapyr, and triclopyr were efficacious and provided 39 to 99% control of alligatorweed, cattail and primrose in 19 of the 20 trials. There were no significant differences i n product performance except glyphosate vs. alligatorweed (trial 1, Rodeo vs. Roundup Custom) and glyphosate vs. cattail (trial 1, Rodeo vs. Glyphosate 5.4). These results demonstrate under small -scale conditions, the majority of the generic and proprietary herbicides provided similar control of emergent vegetation, regardless of active ingredient

This research evaluated low concentrations and short exposure times of the recently registered aquatic herbicide florpyrauxifen-benzyl (4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)-5-fluoro-pyridine-2-benzyl ester) on the target plant Eurasian watermilfoil (Myriophyllum spicatum L., hereafter referred to as EWM) as well as selectivity towards the nontarget submersed species Illinois pondweed (Potamogeton illinoensis Morong), elodea (Elodea canadensis Michx.), and coontail (Ceratophyllum demersum L.)

The nonnative Brazilian egeria (Egeria densa Planch.) is the dominant submersed plant in the Sacramento-San Joaquin River Delta, displacing native plant species and degrading habitat for endangered fish species. A mesocosm study was conducted at the U.S. Department of Agriculture (USDA) facility in Davis, CA to determine efficacy of aquatic herbicides on egeria. Fifty mesocosm tanks of 167 L capacity were planted with four 4.2-L pots of egeria. Four tanks each were treated with bispyribac sodium (45 mu g L-1), carfentrazone-ethyl (200 mu g L-1), ethylenediamine chelate of copper (1,000 mu g L-1), diquat (390 mu g L-1), dipotassium salt of endothall (5,000 mu g L-1), dimethylalkylamine salt of endothall (5,000 mu g L-1), florpyrauxifen-benzyl (50 mu g L-1), flumioxazin (400 mu g L-1), fluridone (60 mu g L-1), imazamox (500 mu g L-1), penoxsulam (60 mu g L-1), and four tanks were left as an untreated reference. All were single treatments, static exposures for 10 wk. At the end of 10 wk, all pots were harvested, and the shoots were dried at 70 C for 48 h. All herbicides produced some statistically significant reduction in biomass. Copper, diquat, endothall dimethylalkylamine, and fluridone produced > 90% control. Carfentrazone (69%) and the potassium salt of endothall (62%) provided greater than 50% control, with other herbicides producing somewhat less than 50% control. Field demonstration has substantiated some of these findings. A study of three treatment plots in 2016 found an 85% reduction in biomass in fluridone-treated plots, compared to a 26% increase in biomass in untreated plots. A field trial on two plots treated with diquat found 98% and 80% control, respectively. A field trial with the dipotassium salt of endothall resulted in 43% control after one treatment.

Flowering rush (Butomus umbellatus L.) possesses a dynamic ability to establish and thrive in the littoral zones of quiescent and flowing water systems, either as an emergent plant along shorelines (up to 1.3 m) or as a submersed plant in deeper water (up to 6 m) (Countryman 1970, Madsen et al. 2016c). Once established, flowering rush can form monotypic stands that crowd out desirable native vegetation, limit recreational water use, reduce water flow, and impact native fish species (Boutwell 1990, Parkinson et al. 2010). Subsequently, its ability to grow in a variety of habitats and conditions has led to its spread and establishment in water bodies where a high rate of water exchange can occur over a relatively short period of time. This presents a unique challenge for the management of this species using submersed herbicide applications because water exchange can be too rapid to maintain adequate herbicide concentrations in potential treatment areas (Getsinger et al. 1996). One such waterbody is the McNary Reservoir (Wallula Lake; 15,378 ha) on the Columbia River in the tricities area of Washington State. McNary is a run-of-the-river reservoir, and as such acts as a hydrodynamic system—with constantly flowing water. Flowering rush was first reported in the upper portion of the reservoir at the mouth of the Yakima River in 2008. As of 2019, the plant has been documented at numerous locations within the reservoir, in small, isolated patches and stands , 1 ha in size. The majority of the flowering rush in these locations never breaks the water surface and remains in the submersed growth habit. In the shallow littoral zones (1 to 2 m) adjacent to the reservoir shoreline, flowering rush grows in mixed stands of other submersed species (e.g., elodea, milfoils, pondweeds); however, in deeper areas (2 to 6 m) there is limited competitive pressure from other submersed plants. This dynamic reservoir system presents a complex matrix to determine which treatment options will be best to control flowering rush—particularly using herbicides in short concentration exposure time (CET) settings. Water exchange evaluations at multiple flowering rush sites during 2018 and 2019 demonstrated that rhodamine WT (RWT) dye dissipated quickly, and dye half-lives ranged between 0.5 and 8.0 h. Currently, there are limited strategies for providing long-term selective control of flowering rush, particularly in hydrodynamic systems. Attempts to mechanically harvest flowering rush in Detroit Lakes, MN, during the 1990s and 2000s were ineffective (Marko et al. 2015) and likely resulted in its spread throughout the watershed due to the displacement of rhizomes and rhizome buds, which are an important factor for flowering rush dispersal (Hroudova et al. 1996). Turnage et al. (2019b) documented mechanical clipping of flowering rush shoots to be an effective management technique; however, it did not provide any additional level of control in comparison to sequential herbicide applications. Inefficiencies associated with timely removal and disposal of clipped/harvested vegetation and high operating costs (Bryant 1970, Bryant 1974, Culpepper and Decell 1978, Haller 2009) further limit the use of mechanical control for large-scale flowering rush management operations. At present, there are no biological control agents available for flowering rush. Small-scale research and field demonstrations have documented some success with submersed treatments of contact herbicides, but multiple treatments are often necessary to provide acceptable levels of control (Poovey et al. 2012, Poovey et al. 2013, Madsen et al. 2016a,b, Parsons et al. 2019, Turnage et al. 2019a,b). Water exchange evaluations with RWT dye, in conjunction with endothall (dipotassium salt, 3 mg L1 ) or diquat (0.37 mg L1 ) treatments targeting flowering rush at Detroit Lakes, MN, revealed that dye concentrations dissipated quickly (half-life: 2 to 12 h) out of treatment plots (Skogerboe 2010). Subsequently, endothall treatments were not effective at reducing above- or belowground biomass following a single treatment; however, two sequential diquat treatments (0.37 mg L1 ) were deemed effective at reducing aboveground biomass (Madsen et al. 2012). Additional larger scale field demonstrations at Detroit Lakes, MN, ultimately showed that multiple diquat treatments annually were effective in reducing above- and belowground biomass as well as rhizome bud density with minimal adverse effects on native plant communities (Madsen et al. 2013, Madsen et al. 2016b, Turnage et al. 2016). These findings indicate that sequential contact herbicide treatments on an annual basis can contribute to long-term flowering rush control by reducing vegetative growth and exhausting energy reserves (i.e., roots, rhizomes). To date, small-scale research evaluating contact herbicides under short (e.g., less than 6 h) CETs for the management of flowering rush is lacking, because much of the available literature has primarily focused on submersed species such as hydrilla (Hydrilla verticillata L.f. Royle) and Eurasian watermilfoil (Myriophyllum spicatum L.) (Netherland et al. 1991, Poovey and Skogerboe 2003, Glomski et al. 2005, Skogerboe et al. 2006, Mudge and Theel 2011). In addition, a commercially available premix formulation of diquat plus endothall (hereafter referred to as diquat plus endothall) has not been previously evaluated for flowering rush control. Therefore, the objective of this study was to evaluate maximum concentrations of the herbicides diquat, endothall, and diquat plus endothall, across a range of short exposure times, for managing flowering rush. It is hypothesized that the diquat and diquat plus endothall treatment will perform similarly, because the diquat concentration is essentially equivalent when each is applied at the maximum labeled rate. However, diquat plus endothall labeling allows for drip or metered applications in nonirrigation, flowing water sites (United Phosphorous Inc. 2017); whereas other available aquatic use diquat products do not have the necessary labeling language for these applications. Thus, providing these data is beneficial for resources managers because it offers supporting documentation to pursue proper permitting and the development of appropriate management plans linked to water exchange processes specific to the targeted treatment area, particularly in sites where a drip or metered application might be warranted.

US Environmental Protection Agency (USEPA) approved algaecides and herbicides are frequently utilized to manage nuisance algae and aquatic macrophytes. However, there is limited information available on the effectiveness of these products for the management of starry stonewort. Thus, the goal of this research was to discern effective chemical control products for later growth stages of starry stonewort using mesocosm studies. Eleven treatments were evaluated using various combinations of four copper-based products, endothall, diquat, and carfentrazone – all with USEPA registrations for use in aquatic sites. To assess treatment efficacy, water quality, photophysiology, biomass changes, and bulbil viability were evaluated. Nine of the eleven treatments yielded lower dissolved oxygen concentrations and higher specific conductance when compared to the control. Photophysiological response varied by condition, but seven of eleven treatments resulted in significantly lower fluorescent and maximum fluorescent yield. Five of these also exhibited significantly lower average photosynthetic yields, with combination treatments resulting in more drastic decreases. Ten of the eleven treatments had significantly less biomass compared to the control when measured via wet weight; however, only four treatments were significant when measured via dry weight. Lastly, all conditions utilizing copper-based products significantly reduced bulbil viability while non-copper products had no impact.

Herbicide selection is key to efficiently managing nuisance vegetation in our nation’s waterways. After selecting the active ingredient, there still remains multiple proprietary and generic products to choose from. Recent small-scale research has been conducted to compare the efficacy of these herbicides against floating and emergent species. Therefore, a series of mesocosm and growth chamber trials were conducted to evaluate subsurface applications of the following herbicides against submersed plants: diquat versus coontail (Ceratophyllum demersum L.), hydrilla (Hydrilla verticillata L.f. Royle), southern naiad (Najas guadalupensis (Sprengel) Magnus), and Eurasian watermilfoil (Myriophyllum spicatum L.); flumioxazin versus coontail, hydrilla, and Eurasian watermilfoil; and triclopyr against Eurasian watermilfoil. All active ingredients were applied at concentrations commonly used to manage these species in public waters. Visually, all herbicides within a particular active ingredient performed similarly with regard to the onset and severity of injury symptoms throughout the trials. All trials, except diquat versus Eurasian watermilfoil, resulted in no differences in efficacy among the 14 proprietary and generic herbicides tested, and all herbicides provided 43%–100% control, regardless of active ingredient and trial. Under mesocosm and growth chamber conditions, the majority of the generic and proprietary herbicides evaluated against submersed plants provided similar control.