Investigation of Updates Aquatic Herbicides and Newer Technologies for Controlling Aquatic Pests in Water Conveyance Systems in the Western United States
There are only three aquatic herbicides labeled for irrigation canals. These three aquatic herbicides have undergone reregistration by the U.S. Environmental Protection Agency (EPA). This process has involved strict investigations on fate, toxicity, and environmental impact. If registration is cancelled by EPA on any of these three aquatic herbicides, Reclamation and irrigation districts in the Western United States will be adversely affected and other Integrated Pest Management (IPM) alternatives (if possible) will have to be rapidly developed.
* Can Reclamation afford to lose any of these registered herbicides for aquatic weed control?
* Should Reclamation be pro-active in finding replacement aquatic herbicides or other non chemical technologies?
* Can new or older herbicides aquatic herbicide be field tested to support crop tolerance data to register new aquatic herbicides?
Alternate methods like hydrogen peroxide, ultrasonic technology, and re-registered aquatic herbicides should be evaluated in multiple use water conveyance systems to provide potential feasible control methods.
Need and Benefit
In the last 20 years, the number of EPA-registered aquatic herbicides has dwindled to three formulations. Each of these formulations has recently undergone EPA re-registration. Each of these compounds was initially developed for primary delivery canals; however, with time these canals now deliver multiple use water for irrigation, drinking supplies, recreation, industrial and municipal purposes. It has becomes more difficult to treat aquatic weeds in canals carrying multiple use water and the current aquatic formulations have to be carefully applied to avoid any potential impact outside any closed conveyance system.
It is imperative to develop substitute aquatic herbicides or new technologies to treat water conveyance systems carrying multiple use water for the future. Acrolein is a restricted-use pesticide due to its inhalation toxicity but is the most widely used herbicide for control of submersed weeds and algae in western irrigation and drainage canals and ditches. Crop tolerance or allowable residue level for drinking water for water treated with acrolein has never been required. Acrolein cannot be used where it can contaminate drinking water, and treated water must be held for six days before release into fish bearing waters. Control of weeds downstream from the injection point may occur over 5 to 10 miles, depending upon flow and application concentration and duration. Acrolein is injected into canal water based upon discharge from nitrogen-pressurized containers to minimize applicator exposure. Reclamation has conducted extensive research on acrolein over the past 50 years. Potential data gaps may exist with acrolein regarding fate, crop tolerance, and environmental impact.
Copper sulfate has been widely used since 1950 for algae control. Copper sulfate efficacy is also significantly reduced in hard and turbid water. In addition, increased regulatory constraints and water quality regulations are making the use of copper formulation for weed control more complicated. Copper is typically applied at 1.0 parts per million (ppm), depending upon flow and weed species for several hours. The applications of copper are sometimes alternated every three to six weeks with acrolein, depending upon the weed species present.
Xylene is typically used in smaller channels with low discharge due to the high concentrations required to control submersed weeds. Xylene could potential leach into ground water. Xylene is applied to irrigation ditches when submersed weed growth gets too mature for effective control with acrolein. Irrigation districts may slow canal flow for these xylene treatments to reduce the amount of the product required for the application. Xylene applications will control the most resistant submersed weeds for greater than 5 miles down the canal, depending on flow velocity and water chemistry. Xylene is exempt from residue tolerances when applied when applied at less than 750 ppm. Xylene is not applied to water which may be used as a potable water source and cannot be discharged into natural waters if xylene residues are greater than 10 ppm.
The purpose of this research is to evaluate new aquatic pest control technologies including Aquathol K, PAK 27 (i.e., hydrogen peroxide) and ultra sonic technology for control of aquatic plants and algae. New technologies like hydrogen peroxide breakdown to hydrogen and water and would potentially have no adverse effect with regard persistence, crop tolerance, aquatic wildlife, and impact to the environment. Ultra-sonic technology is a potential candidate for algae control and has been shown to control algae in static water systems; however, field trials needs to be conducted in flowing water system to see what effect this technology has on filamentous algae which occur frequently on concrete lined canals in the Western United States.
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