Abstract
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.
Aquatic resource managers are tasked with ensuring that aquatic flora does not hinder navigation, flood control efforts, or other uses of state waters. Most aquatic weeds are managed using herbicides that have been approved by the US Environmental Protection Agency (USEPA) for use in aquatic ecosystems. Coordination of statewide aquatic weed management programs in Florida are provided by the Florida Fish and Wildlife Conservation Commission (FWC), which oversees tens of millions of dollars in federal and state funds to control aquatic plants in Florida’s public waters (FWC 2018, 2019, 2021a, 2021b). Most funding is allocated to management of the submersed weed hydrilla (Hydrilla verticillata), but significant funds are used to control other species as well. For example, in fiscal year 2020–21, a total of $14,110,829 in federal and state monies were used for aquatic plant management. Of that, $8.026 million was used for hydrilla control, $4.120 million for floating plant control [primarily waterhyacinth (Eichhornia crassipes) and waterlettuce (Pistia stratiotes)], and $1.830 million for “other” aquatic plant control (FWC 2021a, 2021b).
Excessive aquatic plants can interfere with flood control operations, water movement efforts, recreational activities, and natural processes that are critical to ecosystem health, such as reducing oxygen and light penetration through the water column (Gettys 2020). Although hydrilla, waterhyacinth, and waterlettuce are the most intensively managed aquatic plants in Florida, there are a number of other species that are targeted for control, including the small floating weeds feathered mosquitofern (Azolla pinnata) and common salvinia (Salvinia minima). Other vexing invaders of Florida’s waters are rotala (Rotala rotundifolia) and crested floatingheart (Nymphoides cristata). Rotala, an amphibious aquatic and wetland plant, is an Asian native that is used as a submersed ornamental in aquaria and as a marginal groundcover in plantings around water gardens (Della Torre et al. 2017; Gettys and Della Torre 2021). It was first reported outside of cultivation in Florida in 1996 (Jacono and Vandiver 2007). Similar to rotala, crested floatingheart is Asian in origin and was first reported in Florida’s waters in 1996 after suspected escapes from cultivation (Burks 2002). This highly ornamental floating-leaved species has proven to be a formidable invader (Gettys et al. 2017; Markovich et al. 2022) and was added to the Florida Noxious Weed list in 2014 (Florida Department of State 2021).
The USEPA will only issue a pesticide label if the product “will not generally cause unreasonable adverse effects on the environment… taking into account the economic, social, and environmental costs and benefits of the use of any pesticide” (USEPA 1996). Despite this assurance, many stakeholders are distrustful of “synthetic” aquatic herbicides and have tasked researchers and aquatic resource managers with finding ways to reduce synthetic herbicide use. These efforts include exploring the effects of “natural” herbicides that are sometimes used in home gardens and organic farming. Gettys et al. (2021) reviewed the literature regarding some of the “natural” herbicides used for terrestrial weed control, and then evaluated the efficacy and selectivity of acetic acid, d-limonene, and combinations of the two on waterhyacinth, waterlettuce, pickerelweed (Pontederia cordata), and broadleaf sagittaria (Sagittaria latifolia). They reported that some combinations of acetic acid and d-limonene were efficacious on invasive waterhyacinth and waterlettuce and selective on native pickerelweed and broadleaf sagittaria, but that product and labor costs would likely be much greater than those associated with synthetic herbicides (Gettys et al. 2021). Gettys et al. (2022) continued this vein of research by evaluating the effects of acetic acid and d-limonene on the invasive species feathered mosquitofern and common salvinia and the native plants gulf coast spikerush (Eleocharis cellulosa) and cattail (Typha latifolia) and reported similar results. In addition to the fiscal barriers presented by the “natural” herbicides, acetic acid and d-limonene are not labeled for use as aquatic herbicides at the concentrations evaluated, so information needed for USEPA approval (i.e., environmental fate, ecological toxicity, etc.) may be unavailable (Stubbs and Layne 2020).
Based on previous work reported by Gettys et al. (2021, 2022), our objectives were to evaluate efficacy and selectivity of acetic acid and d-limonene (alone and in combinations) on two invasive target species and two desirable nontarget species, and to compare the costs of using these products vs. the synthetic USEPA-approved aquatic herbicide diquat dibromide. All three products evaluated in these experiments function as contact herbicides and are therefore not translocated throughout the treated plants. As with other contact herbicides, selectivity is highly dependent on coverage (e.g., plants only show phytotoxicity symptoms after direct exposure to the product being used).
Materials and methods
Efficacy and selectivity studies
Target (weed) species were rotala and crested floatingheart, and nontarget (desirable) species were spatterdock (Nuphar advena) and giant bulrush (Schoenoplectus californicus). Plants were treated in pairs of one target species and one nontarget species. “Run 1” focused on rotala and spatterdock, whereas “Run 2” focused on crested floatingheart and giant bulrush.
Rotala and crested floatingheart were sourced from populations maintained at the University of Florida Fort Lauderdale Research and Education Center (FLREC) in Davie, FL, USA, and spatterdock and giant bulrush were purchased from an aquatic nursery (Aquatic Plants of Florida, Myakka City, FL, USA) and transported to FLREC. Plants were grown in 2-L plastic pots without holes that were filled with sand [grain diameter 0.25–0.5 mm (Multi-Purpose Sand; Sakrete, Charlotte, NC, USA)] amended with 4 g of 15N–3.9P–10K controlled-release fertilizer formulated for 6-month release in Florida (Osmocote Plus; ICL Specialty Fertilizers, Dublin, OH, USA). Each pot was planted with ten 15-cm-long apical cuttings (rotala) or a single plant (crested floatingheart, spatterdock, or giant bulrush). Pots of crested floatingheart and spatterdock were placed in 18-gal plastic tubs filled with well water, whereas rotala and giant bulrush were grown out on greenhouse benches and irrigated twice per day (10:00 am and 4:00 pm) with the equivalent of 1/2 inch of water per irrigation. Plants were grown out for 6 weeks to allow establishment, then one bench-grown plant was introduced to each tub (water depth ∼4 inches above the surface of the pots) and treatments were applied. At the time of treatment, all leaves of crested floatingheart and spatterdock were on or above the surface of the water, as was most biomass of rotala and giant bulrush (∼20 cm and ∼120 cm, respectively).
Plants were treated once with a “spray to wet” application (50 mL solution per mesocosm) to above-water foliage and all treatments included 1% v/v of a nonionic surfactant (Induce; Helena Agri-Enterprises, LLC, Collierville, TN, USA). Nine single-product treatments (5%, 7.5%, 10%, 15%, and 20% acetic acid; 10%, 15%, 20%, and 30% d-limonene), 20 combination treatments (all combinations of single acetic acid and d-limonene treatments), three synthetic standard-practice treatments (0.22%, 0.45%, and 0.89% diquat dibromide), and an untreated control were evaluated. We prepared four replicates of each treatment. The concentrates used to prepare treatment solutions were 30% acetic acid (Green Gobbler 30% Vinegar Home and Garden; CC Holdings, Inc., Gurnee, IL, USA), 100% d-limonene (100% Pure Technical Grade D-Limonene; CC Holdings, Inc.), and 37.3% diquat dibromide (Tribune Herbicide; Syngenta Crop Protection, LLC, Greensboro, NC, USA). Treatments were applied to Run 1 (rotala and spatterdock) and Run 2 (crested floatingheart and giant bulrush) plants on 6 Dec 2021 and 28 Mar 2022, respectively.
We monitored plants for 8 weeks after treatment and then scored them for visual quality using a 0 to 10 numerical scale, where 0 = dead; 5 = fair quality, acceptable, somewhat desirable form and color, little to no chlorosis or necrosis; and 10 = excellent quality, perfect condition, healthy and robust, excellent color and form. As with Gettys et al. (2021, 2022), we evaluated quality instead of injury or damage, as quality can be used to measure plant response to treatments. We then conducted a destructive harvest and collected all live biomass above the surface of the substrate. Harvested materials were placed in paper bags and transferred to a forced-air oven maintained at 65 °C for 2 weeks before being weighed. Visual evaluations and destructive harvests occurred on 30 to 31 Jan 2022 (Run 1) and 23 to 24 May 2022 (Run 2).
Visual quality data were arcsine transformed to normalize distribution before statistical analysis. Data within a species were evaluated using a generalized linear model (SAS version 9.4; SAS Institute, Cary, NC, USA) to identify treatment means that differed from those of untreated plants at P = 0.05. Treatment means of visual values and dried biomass were then compared with untreated controls. An ideal herbicide treatment should cause a > 90% reduction in target weed quality and biomass (i.e., be efficacious) and a < 50% reduction in these traits in nontarget native plants (i.e., be selective) (Haller and Gettys 2013). Therefore, our benchmark for efficacy on the target weeds rotala and crested floatingheart was a > 90% reduction and our indicator of selectivity on the native plants spatterdock and giant bulrush was a < 50% reduction compared with untreated plants.
Cost comparisons
Most diquat dibromide used by FWC in fiscal year 2018–19 was applied as Tribune (Clark and Dew 2019) and was purchased for $35.50/gal, which was used for cost comparisons. As mentioned previously, the base “natural” products used in these experiments were 30% acetic acid and technical grade d-limonene. Bulk (275-gal tote) 30% acetic acid was $8.00/gal and bulk (4 × 55-gal drums) technical grade d-limonene was $31.82/gal (CC Holdings, Inc. 2022).
Results and discussion
Single products
Diquat dibromide at 0.22%, 0.45%, and 0.89% reduced live biomass of rotala, crested floatingheart, and native giant bulrush by > 90% but spatterdock was less affected, with biomass reductions of 40% to 50% compared with untreated plants. As reported by Gettys et al. (2021, 2022), an objective of these experiments was to compare the efficacy of natural products with the synthetic herbicide diquat dibromide, but it was clear that most natural treatments were much less effective than diquat dibromide and comparisons between natural treatments and untreated controls would be more informative. Thus, diquat dibromide treatments were removed from datasets before further statistical analyses were conducted.
Single-product natural treatments did not affect biomass of rotala (P = 0.228), crested floatingheart (P = 0.874), or the native spatterdock (P = 0.099). Biomass of treated giant bulrush was greater than or similar to that of untreated plants [P = 0.001 (Fig. 1)]. Visual quality responses followed a similar trend, with rotala, crested floatingheart, and native spatterdock visual quality values unaffected (P = 0.436, 0.184, and 0.238, respectively). Giant bulrush visual quality was reduced by treatments with any concentration of acetic acid, but plants treated with any concentration of d-limonene had visual quality values that were similar to untreated plants [P < 0.001 (Fig. 2)].
Biomass of giant bulrush 8 weeks after single-product treatment. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants; 1 g = 0.0353 oz.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Biomass of giant bulrush 8 weeks after single-product treatment. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants; 1 g = 0.0353 oz.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Biomass of giant bulrush 8 weeks after single-product treatment. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants; 1 g = 0.0353 oz.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Visual quality of giant bulrush 8 weeks after single-product treatment. A numerical scale of 0 through 10 is used to describe visual quality, where 0 = dead; 5 = fair quality, acceptable, somewhat desirable form and color, little to no chlorosis or necrosis; and 10 = excellent quality, perfect condition, healthy and robust, excellent color and form. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Visual quality of giant bulrush 8 weeks after single-product treatment. A numerical scale of 0 through 10 is used to describe visual quality, where 0 = dead; 5 = fair quality, acceptable, somewhat desirable form and color, little to no chlorosis or necrosis; and 10 = excellent quality, perfect condition, healthy and robust, excellent color and form. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Visual quality of giant bulrush 8 weeks after single-product treatment. A numerical scale of 0 through 10 is used to describe visual quality, where 0 = dead; 5 = fair quality, acceptable, somewhat desirable form and color, little to no chlorosis or necrosis; and 10 = excellent quality, perfect condition, healthy and robust, excellent color and form. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Acetic acid and d-limonene mixes
Combinations of acetic acid and d-limonene reduced rotala biomass [P = 0.011 (Fig. 3)] by 60% to 99% and visual quality [P = 0.008 (Fig. 4A)] by 25% to 98% compared with untreated controls. Bulrush biomass was unaffected (P = 0.055) by combination treatments; visual quality was impacted [P < 0.001 (Fig. 4B)], but only one treatment reduced bulrush visual quality by > 50% compared with untreated plants. Combination treatments did not affect crested floatingheart biomass or visual quality (P = 0.262 and 0.184, respectively) or spatterdock biomass and visual quality (P = 0.803 and 0.937, respectively).
Biomass of rotala 8 weeks after treatment with combinations of acetic acid and d-limonene. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants; 1 g = 0.0353 oz.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Biomass of rotala 8 weeks after treatment with combinations of acetic acid and d-limonene. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants; 1 g = 0.0353 oz.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Biomass of rotala 8 weeks after treatment with combinations of acetic acid and d-limonene. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants; 1 g = 0.0353 oz.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Visual quality of (A) rotala and (B) giant bulrush 8 weeks after treatment with combinations of acetic acid and d-limonene. A numerical scale of 0 through 10 is used to describe visual quality, where 0 = dead; 5 = fair quality, acceptable, somewhat desirable form and color, little to no chlorosis or necrosis; and 10 = excellent quality, perfect condition, healthy and robust, excellent color and form. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Visual quality of (A) rotala and (B) giant bulrush 8 weeks after treatment with combinations of acetic acid and d-limonene. A numerical scale of 0 through 10 is used to describe visual quality, where 0 = dead; 5 = fair quality, acceptable, somewhat desirable form and color, little to no chlorosis or necrosis; and 10 = excellent quality, perfect condition, healthy and robust, excellent color and form. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
Visual quality of (A) rotala and (B) giant bulrush 8 weeks after treatment with combinations of acetic acid and d-limonene. A numerical scale of 0 through 10 is used to describe visual quality, where 0 = dead; 5 = fair quality, acceptable, somewhat desirable form and color, little to no chlorosis or necrosis; and 10 = excellent quality, perfect condition, healthy and robust, excellent color and form. Bars are the mean of four replicates and error bars are 1 SD from the mean. Treatments coded with the same letter are not different at P = 0.05. The upper bold horizontal rule indicates the mean of untreated control (UTC) plants, whereas the central and lower bold horizontal rules indicate 50% and 90% reductions compared with UTC plants.
Citation: HortTechnology 33, 2; 10.21273/HORTTECH05168-22
These results suggest that treatments using some combinations of acetic acid and d-limonene may be useful to selectively manage populations of invasive rotala without causing unacceptable levels of damage to the native plants spatterdock and giant bulrush. Acetic acid and d-limonene (alone or in combinations) did not affect biomass or visual quality of invasive crested floatingheart.
Cost comparison of acetic acid and d-limonene mixes to diquat dibromide for rotala management
Diquat dibromide served as the synthetic standard-practice treatment in these experiments and was applied as spot foliar treatments. We evaluated three concentrations (0.22%, 0.45%, and 0.89%) of diquat dibromide, but the lowest concentration completely eliminated all rotala biomass, so calculations are based on spot treatments using a 0.22% solution. As mentioned in the materials and methods section, FWC paid $35.50/gal for 37.3% diquat dibromide, so after dilution to a 0.22% concentration, the final cost of “ready to use” (RTU) mix is $0.1775/gal. If a solution of 0.22% diquat dibromide is applied in a carrier volume equivalent to 100 gal/acre as listed on the herbicide label (Syngenta Crop Protection 2011), the material cost per acre treated with diquat dibromide is $17.75. Calculations for the natural products in these trials are based on purchase prices of $8.00/gal for 30% acetic acid and $31.82/gal for technical grade d-limonene. Therefore, the RTU cost for acetic acid is $1.33/gal (5%), $2.00/gal (7.5%), $2.67/gal (10%), $4.00/gal (15%), and $5.33/gal (20%), and the RTU cost for d-limonene is $3.18/gal (10%), $4.77/gal (15%), $6.36/gal (20%), and $9.55/gal (30%).
Florida FWC treatment reports do not list rotala or the methods used to control the species, but the South Florida Water Management District reportedly treated ∼4266 acres of rotala in their management areas between May 2012 and May 2022 (Thayer J, personal communication). Therefore, the following calculations are based on the assumption that ∼426.6 acres of rotala are treated annually. In our experiments, rotala was completely controlled by 0.22% diquat dibromide. No single-product natural treatments effectively controlled rotala, but most mixes caused significant damage to rotala. Of the mixes that reduced target weed biomass by 90% or greater, the least expensive natural treatment for rotala (5% acetic acid + 10% d-limonene; $1.33 + $3.18) is $4.51/gal RTU, or ∼25 times more expensive than 0.22% diquat dibromide. If a mix of 5% acetic acid + 10% d-limonene in a carrier volume of 100 gal/acre was used to treat 426.6 acres of rotala, material costs would be $192,396.60 vs. $7572.15 to treat with 0.22% diquat dibromide.
These calculations reveal that material costs for rotala management would greatly increase if the synthetic herbicide diquat dibromide was replaced with a mix of acetic acid and d-limonene, but associated treatment costs would likely increase as well. As reported by Gettys et al. (2021, 2022), applications using “natural” products would take longer because of the large volume of base materials needed to fill a boat-mounted spray tank. For example, filling a 100-gal tank once with 0.22% diquat dibromide would require 64 fl oz of 37.3% diquat dibromide added to 99.5 gal of water drawn from the system being treated. Five gallons (53 lb) of concentrated herbicide would make 1000 gal of RTU mix, which would treat 10 acres and could represent an entire day’s work. In contrast, filling the same 100-gal tank once with 5% acetic acid + 10% d-limonene (the least expensive efficacious treatment for rotala) would require ∼17 gal (150 lb) of 30% acetic acid and 10 gal (70 lb) of 100% d-limonene, plus the weight of the containers holding the acetic acid and d-limonene. Most spray boats have limited payloads and little spare space, so applicators would likely have to return to shore and “mix at the ramp” to reload the spray tank after applying 100 gal of RTU natural mix.
Conclusions
The “natural” products examined in these experiments may be useful for selectively controlling the non-native weed rotala without causing excessive damage to the desirable native plants giant bulrush and spatterdock. Single-product treatments with acetic acid or d-limonene were ineffective against rotala and crested floatingheart. Several mixes of these two products were efficacious on rotala and selective for spatterdock and giant bulrush, but no combination provided adequate control of crested floatingheart.
Replacing diquat dibromide with combinations of acetic acid and d-limonene would greatly increase rotala management costs. Treatment of this species with the least expensive efficacious treatment (5% acetic acid + 10% d-limonene) instead of 0.22% diquat dibromide would elevate material costs alone 25-fold, and productivity also would be reduced because of the need to return to the dock and reload after every 100-gal tank is depleted. In addition to cost considerations, it is important to remember that these products are not labeled for use as herbicides in aquatic areas. As such, they have not been subjected to the many tests required before USEPA approval, which include environmental fate and ecological toxicity assessments (Stubbs and Layne 2020), and their effects on aquatic fauna have not been well-characterized. Therefore, as noted by Gettys et al. (2021, 2022), acetic acid and d-limonene could have utility in some areas where synthetic herbicides are discouraged, but broad-scale adoption of these natural products for aquatic weed control is not likely to be an affordable option for most resource managers.
Units
References cited
Burks, KC. 2002 Nymphoides cristata (Roxb.) Kuntze, a recent adventive expanding as a pest plant in Florida Castanea. 67 2 206 211
CC Holdings, Inc. 2022 Cleaners https://greengobbler.com/cleaners [accessed 24 Oct 2022]
Clark, R & Dew, A. 2019 Florida Fish and Wildlife Conservation Commission annual report of pollutant discharges to the surface waters of the state from the application of pesticides 1 Jan 2018 through 31 Dec 2018 https://myfwc.com/media/19111/npdes-2018.pdf [accessed 20 Sep 2022]
Della Torre, CJ III, Gettys, LA, Haller, WT, Ferrell, JA & Leon, R. 2017 Efficacy of aquatic herbicides on dwarf rotala J Aquat Plant Manage. 55 13 18
Florida Department of State 2021 The Florida noxious weed list https://www.flrules.org/gateway/notice_Files.asp?ID=23639596 [accessed 21 Oct 2022]
Florida Fish and Wildlife Conservation Commission 2018 Florida Fish and Wildlife Conservation Commission invasive plant management section annual report of activities conducted under the cooperative aquatic plant control program in Florida public waters for fiscal year 2017–2018 https://myfwc.com/media/19112/annualreport17-18.pdf [accessed 17 Sep 2022]
Florida Fish and Wildlife Conservation Commission 2019 Florida Fish and Wildlife Conservation Commission invasive plant management section annual report of activities conducted under the cooperative aquatic plant control program in Florida public waters for fiscal year 2018–2019 https://myfwc.com/media/22606/annualreport1819_ipm.pdf [accessed 17 Sep 2022]
Florida Fish and Wildlife Conservation Commission 2021a Florida Fish and Wildlife Conservation Commission invasive plant management section annual report of activities conducted under the cooperative aquatic plant control program in Florida public waters for fiscal year 2019–2020 https://myfwc.com/media/25501/annualreport19-20.pdf [accessed 17 Sep 2022]
Florida Fish and Wildlife Conservation Commission 2021b Florida Fish and Wildlife Conservation Commission invasive plant management section annual report of activities conducted under the cooperative aquatic plant control program in Florida public waters for fiscal year 2020–2021 https://myfwc.com/media/28949/annualreport20-21.pdf [accessed 17 Sep 2022]
Gettys, LA. 2020 Waterhyacinth: Florida’s worst floating weed Univ Florida, Inst Food Agric Sci, IFAS Publ SS-AGR-380. https://edis.ifas.ufl.edu/publication/AG385 [accessed 24 Oct 2022]
Gettys, LA & Della Torre, CJ III 2021 Rotala: A new aquatic invader of southern Florida Univ. Florida, Inst. Food Agr. Sci., IFAS Publ. SS-AGR-376. https://edis.ifas.ufl.edu/publication/AG381 [accessed 24 Oct 2022]
Gettys, LA, Della Torre, CJ III, Thayer, KM & Markovich, IJ. 2017 Asexual reproduction and ramet sprouting of crested floatingheart (Nymphoides cristata) J Aquat Plant Manage. 55 83 88
Gettys, LA, Thayer, KL & Sigmon, JW. 2021 Evaluating the effects of acetic acid and d-limonene on four aquatic plants HortTechnology. 31 2 225 233 https://doi.org/10.21273/HORTTECH04769-20
Gettys, LA, Thayer, KL & Sigmon, JW. 2022 Phytotoxic effects of acetic acid and d-limonene on four aquatic plants HortTechnology. 32 2 110 118 https://doi.org/10.21273/HORTTECH04986-21
Haller, WT & Gettys, LA. 2013 Pond, selectivity and irrigation studies on potential new aquatic herbicides Aquatics. 35 2 6 10
Jacono, CC & Vandiver, VV Jr 2007 Rotala rotundifolia, purple loosestrife of the south? Aquatics. 29 1 4 9
Markovich, IJ, Gettys, LA, Thayer, KL, Sigmon, JW & Serrano, D. 2022 Effect of desiccation, burial duration and daylength on ramet sprouting of crested floatingheart (Nymphoides cristata) J Aquat Plant Manage. 60 62 65
Stubbs, D & Layne, CR. 2020 Requirements for registration of aquatic herbicides 155 162 Gettys, LA, Haller, WT & Petty, DG Biology and control of aquatic plants: A best management practices handbook 4th ed Aquatic Ecosystem Restoration Foundation Marietta, GA, USA
Syngenta Crop Protection LLC 2011 Tribune herbicide label https://www.greenbook.net/syngenta-llc/tribune [accessed 8 Jun 2022]
US Environmental Protection Agency 1996 Summary of the Federal Insecticide, Fungicide, and Rodenticide Act https://www.epa.gov/laws-regulations/summary-federal-insecticide-fungicide-and-rodenticide-act [accessed 10 Jul 2022]
