Adjuvants affect duckweed (Lemna minor) control with pelargonic acid

Authors: Webber Iii, Charles; SHREFLER, JAMES - Oklahoma State University; TAYLOR, MERRITT - Oklahoma State University

Submitted to: Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2014
Publication Date: 11/15/2014
Publication URL: http://handle.nal.usda.gov/10113/62121
Citation: Webber III, C.L., Shrefler, J.W., Taylor, M.J. 2014. Adjuvants affect duckweed (Lemna minor) control with pelargonic acid. Journal of Agricultural Science. 6(12):1-8. doi:10.5539/jas.v6n12p1.

Interpretive Summary: Duckweeds are small, free-floating aquatic plants that flourish on stagnant or slow-moving water surfaces throughout the world. They are among the smallest flowering plants, providing food for fish and fowl, but their aggressive and invasive growth often make them formidable aquatic weeds, which when uncontrolled can result in fish kills and death of submerged aquatic plants. Pelargonic acid is a naturally occurring material in many plants, animals, and foods, and AXXE(R) (65% pelargonic acid) is a potential organic herbicide for weed control on land. Our research explored the effectiveness of using pelargonic acid to control duckweeds on the water, both with and without adjuvants, materials often added to spray solutions to enhance herbicide performance. Duckweed was sprayed with 7 rates of pelargonic acid combined with 1 of 3 adjuvant treatments. Visual ratings were used to determine the percentage of duckweed control (percentage dead duckweed plants) at each application rate and adjuvant combination. Duckweed control was measured each day for 11 days after treatment. Duckweed control increased as the pelargonic acid rate increased, whether an adjuvant was used or not. The 8% pelargonic acid rate produced excellent (96.7% or greater) duckweed control for all adjuvant treatments, with consistently better control with the BioLink adjuvant compared to the control where no adjuvant was used. At the 10% application rate, all combinations of pelargonic acid and adjuvants or no adjuvants provided outstanding (98.9% or greater) control at all evaluation dates, with no statistical differences among which adjuvant was used. The research demonstrated the effectiveness of pelargonic acid in controlling duckweed when applied over-the-top. Also, there was often better duckweed control if an adjuvant with 30% garlic extracts and 10% yucca extracts (BioLink) was added to the spray solution. Future research should investigate either a higher percentages of these adjuvants or explore the use of other adjuvants to maximize the effectiveness of pelargonic acid on the over-the-top control of duckweed.

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(R) (65% pelargonic acid) is a potential organic herbicide. Research was conducted to determine the impact of spray adjuvants on duckweed control with pelargonic acid. Duckweed was sprayed with 7 pelargonic acid concentrations (0, 1, 2, 4, 6, 8, and 10% v/v) combined with 1 of 3 adjuvant treatments [control, BioLink (30% garlic extracts, 10% yucca extracts, and 60% water) at 0.5% v:v, and orange oil (90% d'imonene and 10% inert ingredients) at 0.5% v:v]. Visual ratings, measuring percentage duckweed control (percentage dead), were collected at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11 days after treatment (DAT). The experiment was repeated twice using 5 replications. Pelargonic acid phytotoxicity increased as spray concentration increased whether an adjuvant was used or not. The 6% pelargonic acid concentration resulted in 90% or greater duckweed control for all adjuvant treatments (control, BioLink, and Orange Oil) across all evaluation dates (1 DAT – 11 DAT). The addition of either adjuvant applied at the 6% pelargonic acid concentration produced consistently greater duckweed control across all evaluation dates (1 DAT – 11 DAT) compared to the control (no adjuvant). The 8% pelargonic acid rate produced excellent (96.7% or greater) duckweed control for all adjuvant treatments, with consistently better control with the BioLink adjuvant and typically with the orange oil, compared to the control. At the 10% all treatments provided outstanding (98.9% or greater) control at all evaluation dates, with no significant differences among adjuvant treatments. The research demonstrated the effectiveness of pelargonic acid in controlling duckweed when applied over-the-top with often better duckweed control with BioLink. The authors suggest future research should investigate either a higher percentage of these adjuvants or explore the use of other adjuvants to maximize the effectiveness of pelargonic acid on the over-the-top control of duckweed.