Hydrilla (Hydrilla verticillata) is a highly invasive, submersed aquatic plant in the United States that includes three subspecies: H. v. verticillata primarily found in the southern United States, H. v. peregrina common in the mid-Atlantic to northern latitudes, and H. v. lithuanica, which was reported in Hartford County, CT, in 2016. This study aimed to determine whether a chilling period is necessary to break dormancy in H. v. lithuanica turions. Results showed no significant differences in sprouting in turions exposed to different chilling durations of 2, 4, 8, and 16 days at 4 degrees C until 4 days after removal from cold treatment. By the end of the study, turions chilled for >= 8 days exhibited significantly higher sprouting (>97%) compared to the nonchilled control (73%). Additionally, time to 50% sprouting was reduced in chilled turions (2.6 to 3.7 days) compared to nonchilled turions (6.9 to 10.9 days). These results indicate that H. v. lithuanica has a flexible dormancy strategy and high sprouting potential after brief chilling, warranting early season management and posing a risk to regions with variable winters.
Since its introduction in the 1990s, giant salvinia (Salvinia molesta D.S. Mitchell) has rapidly spread to become a serious ecological threat to water bodies across the United States. Overland boat transport is a known vector for aquatic invasive species; however, giant salvinia survival under boat trailer conditions is currently unknown. Therefore, an experiment was conducted and repeated to evaluate giant salvinia survival following desiccation under simulated overland boat trailer conditions. Giant salvinia plants were subjected to four environmental conditions: open-air, plastic boat bunks, wood boat bunks, and carpeted boat bunks for durations of 0.5 to 16 d. Following desiccation periods, moisture loss and survival data were recorded. In open-air conditions, plants did not survive following 12 hr of desiccation. Plants on plastic boat bunks survived 1.5 and 1.9 times longer than on wood or carpeted boat bunks, respectively, in run 1. However, no differences in survival between boat bunk types were observed in run 2, potentially because of higher ambient humidity than in run 1. In run 1, ET90 (estimated exposure time to reach 90% mortality) values for carpet, wood, and plastic boat bunks were 2.7, 3.2, and 5.4 d, respectively. Likewise in run 2, ET90 values for carpet, wood, and plastic boat bunks were 4.6, 5.1, and 5.4 d, respectively. Regardless of run or environment, 100% mortality occurred after 8 d of exposure. These results indicate that giant salvinia may require at least 8 d of desiccation in boat-trailer conditions to prevent spread to new aquatic systems.
Giant salvinia (Salvinia molesta D. S. Mitchell) has established and rapidly spread throughout the southeastern United States, requiring the launch of recurring management programs within infested systems. However, the development of a maintenance control approach similar to aquatic plant management programs in Florida has not yet ensued for giant salvinia. A yearlong mesocosm experiment was conducted to evaluate five management action thresholds (plant percent area coverages [PAC] of 0, 5, 25, 50, or 100 PAC) on overall giant salvinia density, sedimentation, and herbicide input. The 5, 25, 50, and 100 PAC spray treatments required 0.27 to 0.90 g ai year(-1) of total herbicide during experimentation, which equates to 0.9 to 3.0 kg ai ha(-1) per year at operational scale. The amount of herbicide applied increased as the PAC action thresholds increased, though treatment frequency was higher at the lower PAC action thresholds (13.5 and 2.8 applications for 5 and 100 PAC action thresholds, respectively). At experiment conclusion, no differences in ending plant biomass existed among the 0 PAC nontreated plants and the <= 50 PAC treatments. When plants went unmanaged, biomass increased 8 to 82 times that of the herbicide-managed plants. While fewer differences were observed among the treatments concerning mesocosm sediment accumulation, maintaining plants at lower PAC levels resulted in less sedimentation. This research supports the use of maintenance control via frequent herbicide applications to maintain giant salvinia populations at low densities to lessen deleterious impacts, minimizing longterm sediment accumulation, while also reducing herbicide
Invasion by curly-leaved pondweed (Potamogeton crispus L.) (CLP) in North America threatens aquatic ecosystems by displacing native aquatic plants and degrading ecosystem services. We evaluated the role of native plants in limiting CLP invasion at restoration sites and the phenology of CLP at midlatitude United States with a 16-mo outdoor mesocosm experiment and plant surveys at the restored Provo River Delta, Utah (PRD). Mesocosm tanks utilized propagule-containing soil from the PRD to replicate restoration site conditions. Two native species-horned (Zannichellia palustris L.) and sago pondweed [Stuckenia pectinata (L.) Borner]-and CLP were added in six treatments: the three species added on their own, each native species with CLP, and an unplanted control (just PRD soil). Surveys were also conducted at the PRD in 2023 and 2024 to document passive recolonization and CLP invasion. The emergence of abundant plant propagules within experimental tanks limited CLP cover, with an average CLP peak cover of < 8% and no difference in CLP cover between tanks with and without native cuttings. We suspect that abundant native propagule banks also limited CLP invasion at the PRD, with an increase in range, but no increase in the number of survey plots (13 of 75) containing CLP from 2023 to 2024. Finally, observed CLP phenology, with a late spring peak and midsummer senescence, was similar to that observed in the northern United States, suggesting management practices from northern regions could be helpful at mid-latitude sites. Managers should support the establishment of native plants at restoration sites to limit CLP invasion.
The biomass, duration, and concentration (BDC) model predicts responses of harmful algae and cyanobacteria to algaecides. This laboratory study identified algaecide formulations that may be effective and assessed effects of exposure duration and biomass on responses of Microseira wollei from Lake St. Clair, MI. A copper algaecide resulted in the greatest decreases in weight. Exposures may need to be increased (within label rates) to adjust for short contact times. Biomasses ranging two orders of magnitude did not negatively impact efficacy. The BDC model offers a powerful tool for designing M. wollei management strategies while adapting to dynamic biomass and exposure conditions.
Managing harmful algal blooms (HABs) is increasingly complex given the diversity of nuisance algal issues and apparent stochastic nature of HAB distributions over space and time. While remote and field-based sensors (e.g., satellites, in situ sondes, autonomous sampling devices) have advanced HAB monitoring, uncertainty remains in how to integrate data for management decisions. This exploratory study reviewed literature on sensor use for HAB management and engaged experts in HAB management to identify data required for decision-making. Only 2.5% of reviewed studies (n =199) reported remote and field-based sensors used directly for management. Of the few studies available, data were used to prioritize waterbodies potentially needing management, provide early warning systems to initiate more frequent monitoring prior to management, and evaluate effectiveness of management efforts. Expert input provided opinions, perceptions, and examples of how remote sensing and field-based sensor technologies may support HAB management (e.g., when, where, and what to manage and management effectiveness) and identified key data gaps to expand application. Emerging sensor technologies may be useful to identify HAB taxa and horizontal and vertical distribution in the water body. Applying sensor-based data requires integration with traditional methods, real-time use, improved data analysis tools, and clearer communication of uncertainty. As remote sensing and field-based sensor technologies advance, their role in the HAB management decision process will continue to expand, providing critical support for the protection of aquatic health and human safety.
Eurasian watermilfoil (Myriophyllum spicatum; EWM) is an invasive aquatic species that poses significant ecological and economic challenges in freshwater ecosystems such as Bear Lake, a freshwater lake on the Utah-Idaho border. While EWM growth dynamics have been studied across eutrophic lakes, data remain limited for Bear Lake, where unique water chemistry may influence plant growth, herbicide behavior, and effectiveness. This study evaluated the EWM growth and the efficacy of two herbicides, florpyrauxifen-benzyl (FPB) and 2,4-dichlorophenoxyace-tic (2,4-D) acid, in Bear Lake water compared to dechlorinated tap water. EWM shoot fragments were propagated in both water types, and growth parameters-including plant height, shoot number, and biomass-were assessed monthly for 3 mo. Additionally, herbicide degradation was monitored over 72 h (2,4-D) and 384 h (FPB), while efficacy trials assessed biomass reduction after 24-and 48-h exposure times to 2 mg a.e. L-1 (2,4-D) or 0.02 mg a.i. L-1 (FPB). Results indicate that EWM exhibited significantly enhanced growth in Bear Lake water, with higher shoot and biomass production than tap water. Herbicide degradation patterns were similar across water types. In tap water, both FPB and 2,4-D achieved significant biomass reductions after 24 h of exposure compared to Bear Lake water. However, efficacy after 48 h exposure was not statistically different between the two water types. These findings underscore the impact of Bear Lake's unique water chemistry on EWM growth and herbicide efficacy, highlighting the necessity of adapting management strategies to account for specific environmental conditions in nutrient-rich freshwater systems.
Waterhyacinth [Pontederia (Eichhornia) crassipes] is one of the most problematic aquatic weeds in the world, with millions of dollars spent each year to manage populations. A wide range of mechanical or manual, chemical, and biological control strategies have been implemented across waterhyacinth's invaded range, but elevated levels of eutrophication, negative public perception toward herbicides, and the potential for development of herbicide resistance confound the problem. Integrated pest management (IPM) uses a combination of control strategies to provide avenues for more efficient and effective control of waterhyacinth but requires research to ensure that different methods are integrated effectively. This study aimed to investigate the relationship between reduced rate herbicide treatments and biological control agents for integrated waterhyacinth management. For this, the effects of high, medium, and low rates of penoxsulam, as well as maximum and half label rates of diquat, glyphosate, and carfentrazone were combined with herbivory pressure from the biological control agents Neochetina eichhorniae and Megamelus scutellaris in an outdoor mesocosm trial. Dry weights of water-hyacinth at the end of the study were generally lower where herbivory was present, but the extent of the efficacy of IPM depended on the type and rate of herbicide being used. Overall, medium rates of penoxsulam with insect herbivory had similar waterhyacinth dry biomass at the end of the study to high rates of penoxsulam. Half rates of diquat and glyphosate with herbivory were similar to those without herbivory, but many of the treatments were so effective at reducing waterhyacinth biomass that insect survival was low. Hence, investigations of lower herbicide rates and higher insect densities could elucidate promising results. Studies such as these are important to develop techniques for optimal integration of differing control methods for waterhyacinth and other invasive species.
Giant salvinia (Salvinia molesta D. S. Mitchell) presents numerous challenges to water resource management. Innovative chemical control methods, such as unoccupied aerial application systems (UAAS), allow for remote herbicide delivery at very-low-volume (VLV) applications. However, UAAS tank capacities (10 to 40 L) are quite limited compared to standard spray equipment (>= 189 L), which ultimately confines operational functionality. A greenhouse trial investigated the efficacy of diquat, flumioxazin, and glyphosate at varying carrier volumes (23 to 935 L-1) to guide UAAS treatment operations. Results indicated VLV applications (23 L ha(-1)) were most effective with diquat, which reduced plant biomass >= 98% at 4 wk.
Invasive species are one of the foremost threats to global biodiversity, and predicting where they can inhabit is of primary concern for researchers and resource managers. Ecological niche models (ENMs) are a useful tool for addressing this problem. This study focuses on Cyperus blepharoleptos (Cuban bulrush), an aquatic sedge that is invasive in the southeastern United States. To model the ecological niche of C. blepharoleptos, 1,137 records were compiled from North and South America and partitioned into training and testing data. Five BioClim variables (BIO1, BIO7, BIO12, BIO14, and BIO15) were selected as environmental variables for modeling. Conservative and speculative ENMs were constructed for C. blepharoleptos using maximum entropy (Maxent). The ENMs were then used to predict habitat suitability, recent climate, and best-case future climate (high greenhouse gas mitigation) for 2040, and worst-case future climate for 2040 (low mitigation). Recent climate predictions suggest suitable habitat in the Southeast in areas currently uninvaded, namely Georgia, South Carolina, North Carolina, Arkansas, and eastern Texas. Under future climate scenarios, suitable habitat is predicted to expand into Tennessee, Oklahoma, and Virginia. Ultimately, future climate scenarios predict between a 110% and 160% increase in niche area over recent climate predictions. These predictions are compared to previous studies and future research directions are discussed.
Eelgrass (Zostera marina) forms extensive seagrass meadows in coastal embayments at northern latitudes globally and provides habitat for a wide range of species. Eelgrass abundance has been monitored with a point-sampling survey at Izembek and Kinzarof lagoons, in southwest Alaska, since 2007, to provide annual estimates of above-ground biomass and detect change over time. We conducted a power analysis to determine if the current sampling effort would provide sufficient statistical power to have an 80% chance of detecting a >= 25% decline in lagoon-wide mean eelgrass biomass over 5 yr. We found that the current monitoring scheme is unlikely to meet that goal, but the same rate of decline (-5.6% per year) could be detected in 10 yr. We also found that additional sampling per year would not help detect a trend in eelgrass-when-present. Results from other studies suggest that eelgrass presence can change substantially from year to year, and thus continuing to monitor the current sample size ('100 points in Izembek Lagoon, 50 in Kinzarof Lagoon) would be useful to monitor changes in presence. Further evaluation of satellite imagery, when available, could also inform changes in the sampling frame if the extent of eelgrass meadows in each lagoon changes. Continued monitoring of eelgrass in this area could inform management of eelgrass itself or of other species of interest that rely on eel-grass, such as Pacific black brant (Branta bernicla nigricans), under continuing environmental or ecological changes.
Flowering rush is an invasive aquatic plant in North America that has deleterious effects on native ecosystems. There are two cytotypes, a triploid and diploid, and multiple genotypes are contained within the diploid cytotype currently established in the United States. Despite its presence in river drainages connected to estuarine areas, documentation on the salinity tolerance of flowering rush is scarce. Currently, information is limited to anecdotal reports suggesting intolerance to saline conditions. A better understanding of the salinity tolerance of this species is essential to providing insight into its invasive range and better informing management efforts. The following study investigated the sprouting and growth of vegetative propagules from four genotypes of flowering rush when exposed to a range of salinities (0 to 35 parts per thousand [ppt]). Sprouting (experiment 1) and growth (experiment 2) were assessed through benchtop and mesocosm experiments, respectively. Sprouting varied among cytotypes, with triploids tolerating higher salinity levels than diploids. Diploid genotypes showed a decrease in sprouting at concentrations > 5 ppt, while triploid sprouting was equivalent to the control up to 15 ppt. Propagules remained viable following salinity exposures, indicating that populations can likely persist after high-saline events. In the growth study, there was no genotype effect but a significant salinity treatment effect. When averaged across genotypes, mean relative daily growth rate was significantly lower for all treatments when compared to the control, and no differences were detected among treatment at doses > 10 ppt. This study corroborates previous classification of this species as a glycophyte or intolerant to saline conditions.
Mosquito fern (Azolla caroliniana) is a free-floating aquatic fern capable of covering water bodies and outcompeting submersed macrophytes, potentially leading to a loss of biodiversity. Limited evidence suggests that mosquito fern can be controlled with the contact herbicide diquat; however, peer-reviewed literature regarding effects of other contact herbicides labeled for use in aquatic environments on mosquito fern is lacking. The purpose of this work was to conduct two trials to determine the effects of foliar (trial 1) and submersed (trial 2) applications of contact herbicides on mosquito fern. In trial 1, foliar applications of the contact herbicides flumioxazin (0.42 and 0.21 kg ai ha(-1)), carfentrazone-ethyl (0.21 and 0.11 kg ai ha(-1)), endothall (2.39 and 1.20 kg ai ha(-1)), diquat (4.52 and 2.26 kg ai ha(-1)), and copper (1.47 and 0.74 kg ai ha(-1)) were administered and biomass assessed 8 wk after treatment (WAT). In trial 2, submersed applications of flumioxazin (0.4 and 0.2 mg ai L-1), carfentrazone-ethyl (0.2 and 0.1 mg ai L-1), endothall (5.0 and 2.5 mg ai L-1), diquat (0.37 and 0.19 mg ai L-1), and copper (1.0 and 0.5 mg ai L-1) were administered and assessed 8 WAT. Foliar treatments were applied at a target diluent rate of 935.4 L ha(-1); all foliar herbicide treatments included a 1% v:v nonionic surfactant. At 8 WAT, all foliar treatments reduced mosquito-fern biomass compared with nontreated plants, but only high rates of flumioxazin, carfentrazone-ethyl, and both diquat rates reduced biomass 100%. All submersed herbicide treatments except copper reduced mosquito-fern biomass by 8 WAT, but diquat was the only treatment to provide 100% biomass reduction. To our knowledge, this is the only work to document mosquito fern biomass reduction by the herbicides flumioxazin, copper, carfentrazone-ethyl, or endothall. This work should be validated on field populations of mosquito fern before recommendation for operational use.
Limited effective and scalable techniques are available to offset harmful algal blooms proactively. Because light is an influential component of many physiological processes in photoautotrophs, limiting availability could alter growth rates and composition of the algal assemblage. In this research, the U.S. Environmental Protection Agency registered product Aquashade (R) was evaluated, comprised of two colorants, erioglaucine and tartrazine, which are designed to absorb specific light wavelengths upon application to water resources. This study was undertaken using 1 and 2 mg/L Aquashade in South Florida, United States. Our initial data show that Aquashade was able to decrease total algal abundance and decrease cyanobacterial proportion of the algal assemblage at 1 month after treatment (MAT) in mesocosm trials in two Florida ponds. Sustained decreases in cyanobacteria were measured through 4 MAT, although these levels were similar to control mesocosms where there was a shift to more beneficial planktonic green algae possibly due to temperature. Managing intensity and specificity of available light wavelengths can provide water resource managers with an additional avenue toward altering phytoplankton assemblage composition.
Triclopyr was first registered for use in aquatics as the water-soluble triethylamine salt formulation for the control of emersed, submersed, and floating plants. Recently, the oil- and water-soluble triclopyr acid formulation was registered for aquatic use, which allows for basal bark applications to woody plants in sites where standing water is present. Although this has greatly increased applicator flexibility to use basal bark treatments in and around water, field observations of injury to the nontarget species red maple (Acer rubrum L.) and sugarberry (Celtis laevigata Willd.) have been reported following applications to nearby Schinus terebinthifolia during periods of inundation. However, sensitivity of these species to triclopyr that has moved into the water following basal bark treatment is not well understood. Therefore, in-water dose-response studies were conducted in 2021 and 2022 to assess sensitivity of the nontarget species A. rubrum, C. laevigata, and buttonbush (Cephalanthus occidentalis L.), to seven triclopyr concentrations ranging from 0.008 to 125 mg L-1 with an exposure time of 21 d. The effective dose for 50% defoliation (ED50) at 49 d after treatment was 0.15, 0.385 and 1.49 mg L-1 for C. laevigata, A. rubrum, and C. occidentalis, respectively. Longer-term ED50 values for reduction in live cambium tissue were 0.925, 1.408, and 2.519 mg L-1 for A. rubrum, C. laevigata, and C. occidentalis, respectively. Effective doses for 15% defoliation and cambium loss were lower across species and ranged from 0.011 to 1.168 mg L-1 . These data indicate the potential for nontarget damage when triclopyr is present in the water. Additionally, the triclopyr acid concentration ranges tested that resulted in nontarget damage also fall within triclopyr label recommendations for in-water applications of 0.75 to 2.5 mg L-1 . These suggest caution for wetland and aquatic applicators using the triclopyr acid formulation when these desirable nontarget species are present.
People use search engines (e.g., Google) to find online information related to specific questions about aquatic plant management (APM). How people search about APM (e.g., what key words they use and what web sites they click on) is critical information to guide professionals from science-based institutions about best practices for educational programming to reach audiences searching the internet for solutions to control aquatic invasive species. This study examined 113 of the most searched key words relating to APM, and from these key words, 1,130 web sites were categorized into either institutional/governmental, commercial, or mixed purpose/ other. Web-site quantity and web-site rank were recorded for each key word from Google, which controls the vast majority of the search-engine market in the United States. Our results showed there were significantly more commercial web sites present in the first 10 search results and that commercial web sites had the highest rankings overall compared to other categories. Key words that are scientific, specific, or about invasive species were more likely to result in institutional/ governmental web sites. However, key words that are vernacular terms, are negatively framed, or are related to control/ management were more likely to result in commercial web sites. Considering many APM web sites from institutional entities such as universities and government agencies are educationally motivated with an emphasis on science, the use of vernacular, negatively framed, or control/management terms in key-word searches for APM information would likely not result in finding these web sites. Overall, our results highlight likely communication gaps for scientific institutions that can provide useful insight for the creation of web sites, outreach materials, and promotional strategies to target an APM audience.
Failure of biological control to adequately suppress target weeds is sometimes due to thermal limitations of introduced agents. However, adaptation of biological control agents to local climates after release may provide a resource for improving performance of the agents in regions where control has been poor. To date, Cyrtobagous salviniae has not provided adequate control of Salvinia molesta in the northern extent of its invasive range in the United States. This has spurred interest in improving control by identifying and leveraging spatial variation in thermal biology of the agent. To compare cold tolerance of C. salviniae populations, we used a modification of the upper limit of chill injury zone (ULCIZ) metric that we term short-exposure chill injury temperature (SECIT). SECIT reflects the relationship between temperature, exposure duration, and mortality and provides a tool for extracting substantial information about an organism's cold tolerance while reducing the overall effort associated with a comprehensive ULCIZ. Four populations of C. salviniae were sourced from across a latitudinal gradient at field sites in Louisiana and Texas, and SECIT was modeled through a two-factorial assay of chill temperature and exposure durations. SECIT results were then used to predict the estimated mortality of each population based on historical weather data. Differences in SECIT were detected among the four populations (lowest/most cold tolerant:-3.01 C; highest/least cold tolerant:-1.12 C) and when used to estimate mortality based on historical cold events reflects an approximately 183,000 km(2) (36.5%) difference in marginally to highly suitable area of S. molesta-infested watersheds in the southeastern United States. These results demonstrate the utility of SECIT to compare cold tolerance between populations of a biological control agent and provide information that can be used to inform management of aquatic weeds using biological control.
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.
Biological control of giant salvinia (Salvinia molesta Mitchell) with the salvinia weevil (Cyrtobagous salviniae Calder & Sands) is considered the cornerstone of giant salvinia control programs in the southern portion of the invaded U.S. range. However, secondary invasion by Cuban bulrush [ Oxycaryum cubense (Poepp. & Kunth) Lye] onto floating mats of giant salvinia might disrupt the dispersal and impact of the weevil. Additionally, it is uncertain how herbicides used for Cuban bulrush management may impact the weevil via direct or indirect effects. To improve the biological control of giant salvinia and manage Cuban bulrush, it is important to determine the impact (i.e., toxicity) of the aquatic herbicide triclopyr on both the weevil and giant salvinia. Therefore, laboratory and mesocosm studies were conducted to determine the direct and indirect toxicity of triclopyr (1.68 and 3.36 kg acid equivalent [a.e.] ha(-1)) alone and with a nonionic surfactant (0.25% v v(-1)) on adult salvinia weevils and determine the impact of triclopyr on giant salvinia biomass. In laboratory bioassays, the direct application of triclopyr (3.36 kg a.e. ha(-1)) alone and in combination with a nonionic surfactant resulted in 32 and 37% weevil mortality, respectively. The higher rate treatments were different than the reverse osmosis (RO) water treatment but not the nontreated reference 7 days after treatment (DAT). However, no other differences in insect mortality were detected among treatments. Additionally, no differences were detected among treatments when triclopyr was applied to giant salvinia to measure indirect weevil mortality and plant biomass 7 DAT. These results suggest that triclopyr has limited impacts on the salvinia weevil and could be used to control Cuban bulrush in salvinia weevil-rearing sites.
Giant salvinia ( Salvinia molesta) can be found in open water under full sunlight as well as under the dense canopy of trees across the southern United States. To date, most herbicides have been evaluated for efficacy against giant salvinia under full sunlight. Because most herbicides interfere with light- dependent processes, the influence of shade where plant growth is slower and herbicide activity could be hindered should be evaluated. Therefore, a mesocosm trial was conducted to determine the impact of reduced light on the efficacy of carfentrazone, diquat, flumioxazin, glyphosate, metsulfuron, and penoxsulam when applied to the foliage of giant salvinia grown under 0, 30, and 60% shade levels. At 7 wk after treatment (WAT), all herbicides reduced giant salvinia biomass 87 to 100% of the control when plants were cultured under 0% shade. Diquat and glyphosate efficacy was not impacted by light intensity, with biomass reduced $ 97% regardless of light treatment. There were no differences in control for plants grown under the full sunlight or 30% shade treatments and exposed to a foliar application of flumioxazin. However, giant salvinia control decreased by 16 and 27% when treated with carfentrazone and grown under 30 and 60% shade levels, respectively. The greatest impact on efficacy occurred when penoxsulam and metsulfuron were applied to giant salvinia grown under the 30% light intensity and biomass was only decreased 20 and 23%, respectively, compared to 63 to 92% control by these slow-acting systemic herbicides when grown under 30 and 0% shade. These findings suggest that light availability plays a crucial role in herbicide performance and herbicide selection is critical for managing this species in shaded areas.
