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United States Department of Agriculture

Agricultural Research Service

Research Project: ORGANIC AND REDUCED INPUT FRESH MARKET SPECIALTY CROP PRODUCTION SYSTEMS FOR THE SOUTHERN GREAT PLAINS Title: Economic comparison of two application methods for potential organic control of duckweed utilizing pelargonic acid as an aquatic herbicide

Authors
item Taylor, Merritt -
item Webber, Charles
item Webber, Daniel -

Submitted to: The Empirical Econometrics and Quantitative Economics Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2013
Publication Date: N/A

Interpretive Summary: Duckweeds (Lemna spp.) are small, free floating, aquatic plants that flourish on stagnant or slow moving, water surfaces throughout the world. Duckweeds are among the smallest flowering plants, providing food for fish and fowl, but their aggressive growth and invasive tendencies make them formidable aquatic weeds, which when uncontrolled can result in oxygen depletion, fish kills, and death of submerged aquatic plants. Pelargonic acid is a fatty acid naturally occurring in many plants and animals, and present in many foods. Two application methods were compared to determine the potential economic advantage of controlling duckweed under certified organic conditions using pelargonic acid as an aquatic herbicide. Method one (Water Solution Experiment) involved adding pelargonic acid directly to the duckweed infested water in attempt to control the duckweed growing on the water surface. Method two (Over-the-Top Application Experiment) involved the over-the-top application of pelargonic acid directly on the growing duckweed on the water surface. Both experiments were conducted at Lane, Oklahoma, under greenhouse conditions. It was determined that the Over-the-Top method had greater duckweed control with less material at a more cost effective level than the Water Solution Method. Utilizing method two, over-the-top application produced 98% control at approximately $243 per surface hectare. The research demonstrated the effectiveness of pelargonic acid in controlling duckweed when applied over-the-top, resulting in a more precise, environmentally targeted, and cost effective duckweed control method than placing the pelargonic acid directly in the duckweed infested water.

Technical Abstract: Duckweeds (Lemna spp.) are small, free floating, aquatic plants that flourish on stagnant or slow moving, water surfaces throughout the world. Members of the genus are among the smallest flowering plants, providing food for fish and fowl, but their aggressive growth and invasive tendencies make them formidable aquatic weeds, which when uncontrolled can result in oxygen depletion, fish kills, and death of submerged aquatic plants. Pelargonic acid is a fatty acid naturally occurring in many plants and animals, and present in many foods. AXXE® (65% pelargonic acid, BioSafe Systems LLC) is an approved organic herbicide for controlling terrestrial weeds. Two application methods were compared to determine the potential economic advantage of controlling duckweed under certified organic conditions using pelargonic acid as an aquatic herbicide. Method one (Water Solution Experiment) involved adding pelargonic acid to water in attempt to control the duckweed growing on the water surface. Method two (Over-the-Top Application Experiment) involved the over-the-top application of pelargonic acid directly on the growing duckweed on the water surface. Both experiments were conducted at Lane, Oklahoma, under greenhouse conditions. In the Water Solution Experiment, the AXXE® was added to water at 4 dilutions (0.0006%, 0.0015%, 0.006%, and 0.015% v/v) and a control (0% v/v) with 8 replications. Visual ratings were collected 1, 3, and 5 days after treatment (DAT). Duckweed control was less than acceptable (< 10% control) at 0.0006% and 0.0015%, inconsistent at 0.006% (3 to 99% control), but very effective (96 to 100% control) at 0.015%. Although the 0.015% v/v dilution has potential as a duckweed management tool, unfortunately, utilizing this method would be cost prohibitive ($12,680 per surface hectare) for 88% duckweed control. Additional research was then conducted to determine if another application method, Over-the-Top, could reduce the economic barrier with an increase duckweed control compared to the Water Solution method. The Over-the-Top method involved 5 replications with 7 concentrations of pelargonic acid applied at 0, 1, 2, 4, 6, 8, and 10% v/v. Visual ratings were collected at 1, 2, 3, 4, 5, 6, 7, and 10 DAT. Pelargonic acid concentrations of 2% produced at least 98% duckweed control at 5 DAT. Increasing pelargonic acid concentration to 4% provided, at least, 99% control at 5 DAT. One hundred percent duckweed control was achieved with 8% pelargonic acid at 5 DAT, while the 10% concentration produced 100% control starting the first rating date (1 DAT). Utilizing method two, over-the-top application produced 98% control at approximately $243 per surface hectare. The research demonstrated the effectiveness of pelargonic acid in controlling duckweed when applied over-the-top, resulting in a more precise, environmentally targeted, and cost effective duckweed control method than placing the pelargonic acid in the water itself.

Last Modified: 10/23/2014
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