Progress 10/01/03 to 09/30/08
Outputs
OUTPUTS: The development of hydrilla populations that are tolerant to the widely used aquatic herbicide fluridone has precipitated a search for new herbicides that hold the potential for aquatic registration. Over the past 5 years over 150 herbicide and herbicide combinations have been evaluated for activity against hydrilla. Surprisingly, few herbicides control hydrilla, but despite this natural tolerance, 6 herbicides representing 4 modes of action have been labeled for aquatic use/or large scale testing. The ALS inhibitors penoxsulam and imazamox have received full federal aquatic registration (Section 3, FIFRA). Another ALS inhibitor, bispyribac-sodium has been under an EPA Experimental Use Permit (EUP) for nearly 2 years. Flumioxazin, a protox inhibitor, topramezone and quinclorac, a bleacher and an auxin mimic, respectively, have state (Florida) EUP's. Flumioxazin is a contact herbicide and the others are representative of systemic or slow acting enzyme inhibitors. All 6 of these herbicides have use rates of < 500 ppb, and penoxsulam, bispyribac and topramezone have use rates < 50 ppb. The issue of selective hydrilla control is significant when herbicides are used in natural, non-production agriculture. The evaluation of these herbicides on native plants has also been conducted and results indicate a very wide range of sensitivity of native plants to these products. The evaluation and ultimate registration of aquatic herbicides is a slow process with questions on use rate, selectivity and potential water use restrictions on irrigated crops as issues requiring valid answers before agrichemical companies will commit funds toward full aquatic registration. Further research is needed on how these new products will be integrated into current weed management programs and also maintain product stewardship in regard to further resistance development PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: State regulatory personnel and resource managers. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The current widespread use of aquatic herbicides that were registered in the 1950's suggests that new aquatic registrations will also be used for many decades into the future. The ful potential of these herbicides has not been realized at this time. Further research is needed on difficult to control weeds such as cabomba, algae, water-chestnut and problematic pond weeds. Resource managers will also be able to develop resistance management plans to assure these products will be useful into the future. The results of these studies have been widely reported at meetings and shared with regulatory agencies.
Publications
- Mudge, C.R. 2007. Characterization of Flumcoxazin as an Aquatic Herbicide. PhD Dissertation, University of Florida, 120 p.
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Progress 10/01/06 to 09/30/07
Outputs
From 1980-2000 fluridone was widely used in Florida ($12-15 million/year) by public agencies for control of the submersed aquatic weed hydrilla. Fluridone resistant populations of hydrilla were reported in 1999 and the search for, and registration of new herbicides to replace fluridone began. Over 100 of the estimated 325 registered herbicides in the US were screened for activity on hydrilla and evaluated for selectivity and safely to non-target, primarily native aquatic and wetland plants. Most of the registered herbicides (> 200) in the US are either toxic to aquatic animals or is not effective in controlling hydrilla. These studies have over time lead to the granting of full federal aquatic use labels or Experimental Use Permits (EUP). Penoxulam (Galleon) was granted a full EPA registration in July 2007 and imazamox (Clearcast) is currently under EPA review for a full aquatic registration. EUP labels are in force for quinclorac, flumioxazin and bispyribac-sodium. An
EUP is currently being reviewed by EPA/FDACS for one additional compound. These products represent three separate modes of action which will be used to slow/prevent the development of resistance by hydrilla and other aquatic weeds. The use rate or application rates of these products for hydrilla control vary widely. Penoxulam is applied at 5 to 15 ppb, bispyribac-sodium at 25-45 ppb, imazamox at 200 ppb, and flumioxazin at 200-400 ppb. Selectivity studies conducted in mesocosm and greenhouse conditions show a wide variety of responses of native, non-target species to these products. Penoxulam impacts lilies, duckweed, pickerelweed and arrowhead. Bispyribac-sodium has similar effects, but imazamox has no impact on lilies, however is toxic to cattail and bullrush. Flumioxazin selectivity is more variable and depends upon whether this contact herbicide is applied foliarly or to the water column. Application to the water column is affected by water pH which regulates by hydrolysis the
flumioxazin half-life, and therefore, selectivity. Additional herbicides are being screened for hydrilla control and the activity of these new products are being evaluated on additional invasive aquatic plants such as rotala, floating-heart and hygrophila.
Impacts
The development and federal registration of 6 to 8 new compounds for aquatic use will impact aquatic and wetland invasive plant management for several decades. For example, diquat and endothall were first registered for aquatic use in the 1950's, and are still widely used today, some 50 years later. The new compounds and modes of action will once again allow economical control of some of the worst aquatic and wetland weeds in the US. These compounds, once registered, can be developed into a program to lessen or prevent the development of herbicide resistance. These herbicides will allow weed managers not only an opportunity to control hydrilla once again, but will allow management choices depending upon selectivity and native plants that may be present. These choices ultimately cause less damage to the environment and more economical weed control.
Publications
- Koschnick, T.J., M.D. Netherland and W.T. Haller. 2007. Effects of three ALS-inhibitors on five emergent native plant species in Florida. J. Aquat. Plant Manage. 45:47-52.
- Puri, A., G.E. MacDonald, and W.T. Haller. 2007. Stability of fluridone-resistant hydrilla (Hydrilla verticillata) biotypes over time. Weed Science 55:12-15.
- Puri, A., G.E. MacDonald, W.T. Haller and M. Singh. 2007. Growth and reproductive physiology of fluridone-susceptible and resistant hydrilla (Hydrilla verticillata) biotypes. Weed Science 55:441-445.
- Sellers, B.A., J.A. Ferrell, W.T. Haller, P. Mislevey and M. Adjei. 2007. Phytotoxicity of selected herbicides on limpograss (Hemarthria altissima). J. Aquat. Plant Manage. 55:54-58.
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Progress 10/01/05 to 09/30/06
Outputs
The deveopment of fluridone resistant hydrilla populations in Florida has resulted in a search for new herbicides that have acceptable toxicity and residue profiles and provide hydrilla control. Approximately 100 herbicide and herbicide combinations have been evaluated in controlled mesocosm studies. These studies have contributed to the approval (2005-06) of Experimental Use Permits (EUP) for imazamox, bispyribac-sodium, and flumioxazin and a Section 18 registration for penoxulam in Florida.. Field studies this year confirm laboratory studies that the ALS inhibitors(imazamox, penoxulam and bispyribac-sodium) are likely to significantly impact important non-target native species such as arrowhead, pickerelweed, smartweed and other dicots. Additional field studies on selectivity are being conducted to refine use rates and timing of application to determine optimum use patterns and minimize effects on non-target plants. The activity of flumioxazin on hydrilla is
significantly affected by water pH. The half-life of this contact herbicide is less than 60 minutes in water at pH 9, but several days in water of pH <7 as a result of pH on hydrolytic degradation of this herbicide. Hydrilla control results where the half-life of flumioxazin is >0.5 days. Additional contact/exposure time data are being collected to ascertain the CET relationships of this herbicide to hydrilla and other submersed species. The objective of this project is to coninue evaluation of non-ALS inhibitors for hydrilla control and submit data for additional EUP labels for expanded research with different herbicide modes of action.
Impacts
The long term reliance upon 6-8 aquatic registrations of herbidides for aquatic and wetland weed management in the US is resulting in the develpment of herbicide resistant weed populations. These populations require greater herbidide use with increased costs and increased non-target damage to native plants. The evaluation and development of new aquatic registrations for new, and potentially less toxic herbicides for aquatic use will greatly assist aquatic and wetland plant managers in their control programs of non-native invasive plants in these natural areas. These new herbicides will result in reduced application rates, additional selectivity, longer term control and protect against the development of herbicide resistance.
Publications
- Koschnick, T. J., W. T. Haller and L. Glasgow. 2006. Documentation of landoltia (Landoltia punctata) resistance to diquat. Weed Science 54:615-619.
- Koschnick, T. J. and W. T. Haller. 2006. Effects of copper chelating agents on diquat activity in diquat resitant landoltia. J. Aquat. Plant Manage. 44:125-132
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Progress 10/01/04 to 09/30/05
Outputs
There are approximately 225 herbicides registered for use in the United States, and 9 products registered for aquatic plant management. Over the past year we have evaluated nearly 50 herbicides, registered for terrestrial uses, for their potential for hydrilla control. These herbicides were selected for evaluation based upon their low toxicities to zooplankton/fish and potential half-lives (7-28 days) in aqueous conditions. Initial evaluations were applied to 74-liter plastic tubs containing four 2-liter pots filled with osmocote amended sand planted with six apical hydrilla sections. Herbicide treatment rates depended on use rates in terrestrial systems but typically were 0 (control), 50, 100, 200, 400 and 800 ppb/l. Hydrilla was exposed to single treatments and harvested 8 weeks after herbicide application. Hydrilla biomass (g. dry weight) was determined for each rate of application. Herbicides that showed at least a 60% reduction in biomass compared to controls
were evaluated further in replicated studies bracketing the rate(s) where hydrilla biomass was most reduced. Based upon these studies imazamox, penoxulam, bispyribac-sodium, and flumioxazin were chosen for additional studies. Currently imazamox and penoxulam have EPA Experimental Use Permits (EUPs) and flumioxazin and bispyribac-sodium are currently being reviewed by EPA for issuance of an EUP. Projected use rates of penoxulam and bispyribac-sodium is 10-25 ppb/l, and of imazamox 75-100 ppb/l and flumioxazin at 400 ppb/l. The first 3 listed products are ALS inhibitors and all are non-selective against several broadleaf native species, including pickerelweed, water hyachinth, frogsbit and other species, but grasses are quite tolerant at these projected application rates. Additional studies are in progress to discover and register alternative products to supplement the ALS inhibitors.
Impacts
The registration of new herbicides for aquatic use will provide lake managers with new options for weed management to reduce incidence of development of resistance and improve control of invasive species in natural areas.
Publications
- Koschnick, T. J., W. T. Haller and A. M. Fox. 2005. Turf and ornamental plant tolerances to endothall in irrigation water II. Turf species. Hort Technology. 15(2):324-329.
- Koschnick, T. J., W. T. Haller and G. E. MacDonald. 2005. Turf and ornamental plant tolerances to endothall in irrigation water I. Ornamental species. Hort Technology. 15(2): 318-323.
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