Duckweed control with over-the-top application of pelargonic acid

Authors: Webber Iii, Charles; WEBBER, DANEL - University Of Arkansas

Submitted to: Journal of Environmental Monitoring and Restoration
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2012
Publication Date: 2/29/2012
Citation: Webber III, C.L., Webber, D.M. 2012. Duckweed control with over-the-top application of pelargonic acid. Journal of Environmental Monitoring and Restoration. 7:78-86.

Interpretive Summary: Duckweeds (Lemna spp. L.) are small, free floating aquatic plants that flourish on stagnant or slow moving water surfaces throughout the continental U.S. Members of the genus are among the smallest flowering plants with a prolific growth rate. Duckweed is a natural food source for fish and fowl, and is invasive because it is easily transported to new locations by transient water fowl where it quickly exploits suitable environments. Greenhouse research was conducted at Lane, OK, to determine the feasibility of applying pelargonic acid as a contact over-the-top aquatic herbicide to control duckweed. Research treatments included 5 replications with 7 concentrations of pelargonic acid applied at 0, 1, 2, 4, 6, 8, and 10% v/v. Over-the-top applications of pelargonic acid effectively controlled duckweed at rates as low as 2% v/v concentrations and provide 100% duckweed control with 8 to 10% v/v concentrations. Pelargonic acid over-the-top applications were shown to be 130 times more effective than adding the material to the pond or lake water. This research provides a method for naturally controlling duckweeds in an environmental friendly manner for land owners and government agencies. Future research should investigate the impact of application volume and adjuvants on duckweed control efficacy.

Technical Abstract: Duckweeds (Lemna spp.) are small, free floating, aquatic plants that flourish on stagnant, or slow moving, water surfaces throughout the continental U.S. 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. It has been demonstrated that pelargonic acid, a potential organic herbicide under development for terrestrial weed control, can control duckweed when added to water in which the duckweed is growing. Greenhouse research was conducted at Lane, OK, to determine the feasibility of applying pelargonic acid as a contact over-the-top aquatic herbicide to control duckweed. Research treatments included 5 replications with 7 concentrations of pelargonic acid (AXXE, 65% pelargonic acid, BioSafe Systems LLC) applied at 0, 1, 2, 4, 6, 8, and 10% v/v. The experiment was repeated twice. Pelargonic acid was applied with a CO2 sprayer equipped with an extended range, stainless steel, 1.51 L min**-1 nozzle at an application volume of 374 L ha**-1 at 2.75 bars over-the-top of the duckweed. The experiment was repeated twice. Visual ratings were collected at 1, 2, 3, 4, 5, 6, 7, and 10 days after treatment (DAT). Lethal dose 50 (LD50) and LD90 for each rating date after treatment were determined using logistic polynomial regression calculations. Pelargonic acid concentrations of 2% produced at least 96% duckweed control at 2 to 10 DAT. Increasing pelargonic acid concentration to 4 to 10% pelargonic acid provided at least 99% control from 3 to 10 DAT. One hundred percent duckweed control was achieved for 8% pelargonic acid from 5 to 10 DAT, while the 10% concentration produced 100% control starting the first rating date (1 DAT). The effectiveness of pelargonic acid in controlling duckweed was demonstrated when application was over-the-top, resulting in a more precise, environmentally targeted, and cost effective duckweed control method than previously reported.