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The foundation of most aquatic weed management programs in Florida is synthetic herbicides because many of these U.S. Environmental Protection Agency (USEPA)-registered products are effective, selective, and inexpensive compared with other strategies such as mechanical harvesting. However, stakeholders have expressed concern regarding their use and managers are interested in exploring alternative methods for aquatic weed control. To that end, we evaluated the efficacy, selectivity, and costs of the “natural” products acetic acid and d-limonene (alone and in combination with each other and citric acid) on the invasive floating plants waterhyacinth ( Eichhornia crassipes ) and waterlettuce ( Pistia stratiotes ), and the native emergent plants broadleaf sagittaria ( Sagittaria latifolia ) and pickerelweed ( Pontederia cordata ). These products, plus an industry-standard synthetic herbicide (diquat dibromide), were applied once as foliar treatments to healthy plants, which were grown out for 8 weeks after treatment to allow development of phytotoxicity symptoms. A 0.22% concentration of diquat dibromide eliminated all vegetation, but neither “natural” product alone provided acceptable (>80%) control of floating weeds, even when applied at the maximum concentrations under evaluation (20% acetic acid, 30% d-limonene). Citric acid (5% or 10%) had no effect on the activity of acetic acid or d-limonene, but some combinations of acetic acid and d-limonene controlled floating weeds effectively without causing unacceptable damage to native plants. However, these treatments are much more expensive than the synthetic standard and managers would realize a 22- to 26-fold increase in product cost alone without factoring in other expenses such as additional labor and application time. Combinations of acetic acid and d-limonene may have utility in some areas where the use of synthetic herbicides is discouraged, but broad-scale deployment of this strategy would likely be prohibitively expensive.

Herbicides that are labeled for aquatic use are often the foundation of aquatic vegetation management programs in the United States because many of these products, which are registered by the U.S. Environmental Protection Agency, are effective, selective, and relatively inexpensive. Resource managers are interested in reducing the use of synthetic herbicides and are considering alternative methods for aquatic weed control. We evaluated the effects of acetic acid and d-limonene on growth of the invasive small floating species feathered mosquitofern ( Azolla pinnata ) and common salvinia ( Salvinia minima ), as well as on the native emergent wetland plants cattail ( Typha latifolia ) and gulf coast spikerush ( Eleocharis cellulosa ). Acetic acid and d-limonene (alone and in combination) were applied once as foliar treatments to healthy plants, which were grown for 8 weeks after treatment to allow for development of phytotoxicity symptoms. All experiments also included diquat dibromide at three concentrations as “industry-standard” treatments for comparison. A 0.22% concentration of diquat dibromide eliminated all vegetation of all species. Most single-product treatments provided good control of invasive feathered mosquitofern with acceptable levels of damage to native gulf coast spikerush, but only 15% and 20% d-limonene treatments were effective on invasive common salvinia and selective for native cattail. Some combinations of acetic acid and d-limonene provided acceptable control of both floating weeds and selectivity for gulf coast spikerush, but all mixes caused unacceptable levels of damage to cattail. Treating these small floating weeds with acetic acid and d-limonene instead of diquat dibromide would increase material costs by 15- to 27-fold. Although these natural products may be useful in some areas where synthetic herbicides are discouraged, they are unlikely to be affordable options for most resource managers.

Most lake, canal, and pond management programs in the United States use herbicides labeled for aquatic use because many of these products, which are registered by the US Environmental Protection Agency, are relatively inexpensive and can effectively control undesirable plants without excessive damage to desirable species. Managers of these resources have expressed an interest in alternative methods for aquatic weed control that could reduce the use of traditional synthetic herbicides. We studied the effects of acetic acid and d-limonene on growth of the invasive aquatic species rotala ( Rotala rotundifolia ) and crested floatingheart ( Nymphoides cristata ), as well as on the native wetland plants spatterdock ( Nuphar advena ) and giant bulrush ( Schoenoplectus californicus ). We applied acetic acid and d-limonene (alone and in combination) once as foliar treatments to healthy plants, then grew out the plants for 8 weeks after treatment to observe damage resulting from treatments. We also evaluated diquat dibromide at three concentrations as “industry-standard” synthetic treatments for comparison. A 0.22% concentration of diquat dibromide eliminated most or all vegetation of rotala, crested floatingheart, and giant bulrush, but was much less damaging to spatterdock. Single-product applications of acetic acid or d-limonene had little effect on any of the four species evaluated. Some combinations of acetic acid and d-limonene provided acceptable control of rotala and selectivity on spatterdock and giant bulrush, but no treatments reduced crested floatingheart growth by more than 40%. Treating rotala with acetic acid and d-limonene instead of diquat dibromide would result in a 25-fold increase in material costs, which would make this option unaffordable for most aquatic system managers.

Increased salinity caused by saltwater intrusion or runoff from de-icing salts can severely affect freshwater vegetation and deteriorate aquatic ecosystems. These habitats can be restored with freshwater ecotypes (locally adapted populations) that tolerate above-normal salinity. Vallisneria americana is a prominent species in many freshwater ecosystems that responds differently to abiotic conditions such as substrate composition and fertility, so, in this study, we evaluated the effects of salt stress on 24 ecotypes of V. americana. Instant Ocean aquarium salt was used to create saline solutions (0.2 to 20.0 parts per thousand (ppt)), then plants were abruptly exposed to these solutions and maintained in these concentrations for five weeks before being visually assessed for quality and destructively harvested. Analysis of variance and nonlinear regression were used to calculate LC50 values—the lethal concentration of salt that reduced plant biomass and quality by 50% compared to control treatment. Growth rate and visual quality varied significantly among ecotypes, and ecotypes that were most and least sensitive to salt had 50% biomass reductions at 0.47 and 9.10 ppt, respectively. All ecotypes survived 10.0 ppt salinity concentration but none survived at 20.0 ppt, which suggests that the maximum salinity concentration tolerated by these ecotypes is between 15.0 and 20.0 ppt.

INTRODUCTION Many water resource managers and state agencies, including the Florida Fish and Wildlife Conservation Commission (FWC), implement aquatic habitat restoration and enhancement projects to reverse changes caused by altered hydrological patterns resulting from water management and control efforts. Submersed aquatic vegetation (SAV) improves fisheries by providing habitat, vegetative cover, and a food source (Wiley et al. 1984, Maceina 1996, Havens et al. 2005, Hanlon and Jordan 2023). [...]many aquatic systems targeted for restoration are degraded with environmental conditions that are very different from less-degraded nearby waterbodies that may serve as sources for restoration materials. [...]locally collected plant material may not fare well when transplanted from a healthy system into a degraded one. Quantitative data such as shoot weight, root weight, and overall plant height can be used to measure the effectiveness of experimental factors (Gettys and Moore 2018). [...]common nursery studies can be used to evaluate the performance of ecotypes under a range of conditions, which could potentially identify plant material that is likely to establish in degraded systems targeted for restoration (Caldwell et al. 2011), and to optimize culture conditions and maximize production of plants for restoration projects, which would reduce the need for field collection of plant material.

Crested floatingheart is a state-listed noxious weed in Florida that reproduces primarily via ramets, rhizome clusters produced at leaf-petiole junctions. Little is known regarding the effect of desiccation, burial duration, and daylength on ramet viability. Fresh ramets were collected and placed on paper towels on a lab bench for 1 to 10 d (to mimic desiccation) or buried for 4 to 24 d under submersed conditions and then unearthed (burial duration). Daylength effects were evaluated by culturing fresh ramets under daylengths ranging from 9 to 15 h. All ramets were planted under submersed conditions after treatment and scored for sprouting for 12 wk after planting (WAP). A single day or more of desiccation greatly reduced ramet viability; the vast majority (97.5%) of fresh ramets had sprouted 4 WAP, whereas only one of the 480 ramets subjected to any desiccation had sprouted by 12 WAP. Burial also inhibited ramet sprouting; 98% of unburied ramets had sprouted 4 WAP, but no ramets buried for any duration sprouted by 12 WAP. Daylength had no effect on ramet sprouting; the vast majority (96.6%) of ramets had sprouted 4 WAP, and only two of the 560 ramets failed to sprout over the 12-wk evaluation period. These results suggest that sprouting of crested floatingheart ramets is unaffected by daylength but is negatively affected by desiccation and burial. These findings provide insight into reproductive strategies in this species and may be useful to resource managers. For example, because desiccation greatly hinders sprouting, resource users should be encouraged to adopt a clean–drain–dry protocol to reduce the spread of this noxious weed.

In flood-control canals, managing submersed vegetation is critical to maintaining rapid water flow during heavy rainfall. Two particularly troublesome species in South Florida’s canals are hygrophila (Hygrophila polysperma) and rotala (Rotala rotundifolia), which grow densely in the water column and impede flow. Due to limited chemical control options, this study evaluated the efficacy of the herbicide florpyrauxifen-benzyl at different concentrations and exposure times for suppressing these invasive plants. Submersed hygrophila and rotala were exposed to florpyrauxifen-benzyl at concentrations of 0, 2.5, 5, 10, or 20 µg L⁻¹ for 6, 24, or 48 hours. Results showed that hygrophila biomass decreased with higher herbicide concentrations and longer exposure times. Rotala, however, exhibited extreme sensitivity—even the lowest concentration (2.5 µg L⁻¹) and shortest exposure (6 hours) virtually eliminated all biomass. These findings highlight florpyrauxifen-benzyl as a highly effective tool for managing hygrophila and rotala in flow-sensitive systems. The rapid control of rotala at minimal doses suggests that short herbicide exposure periods (e.g., during brief flow reductions) may suffice for suppression. This research provides valuable guidance for resource managers seeking efficient strategies to maintain canal functionality while controlling invasive aquatic vegetation.

Ecosystem structure and biophysical processes mediate biological responses to climate changes, but few studies have examined impacts of this dynamic among upper trophic levels. We investigated ecosystem differences in how diverse seabird populations across the northern hemisphere have responded to changes in regional mixed layer temperature and water column stratification. Using 138 time series of breeding productivity over the past half-century, we show that seabird reproductive productivity has declined in the Arctic and North Atlantic but not in the Pacific during a period of ubiquitous mixed layer warming and regionally-variable stratification trends. Models of breeding productivity and ocean drivers show that seabird responses to climate change vary by ecosystem. Additionally, ecosystems in which seabirds exhibit detectibly declining productivity tend to have lower overall diet diversity across seabird species. These findings emphasize the importance of ecosystem processes and structure in determining the vulnerability of marine predators to climate change. Diet diversity across northern hemisphere ecosystems affects seabird responses to climate change, with breeding productivity declining in the Arctic and North Atlantic but not in the Pacific from 1993 to 2019, based on 138 time series of breeding success and linear mixed effects models.