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Abstract
Charles L. Webber III and Daniel M. Webber. 2011.
Duckweed control with over-the-top
application of pelargonic acid. JEMREST 7:78-86
DOI:
10.4029/2011jemrest7no008
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 previously 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 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 previously reported.
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