ARS | Publication request: Absorption and Translocation of Aminocyclopyrachlor and Aminocyclopyrachlor Methyl Ester in Canada Thistle (Cirsium arvense)

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 2009
Publication Date: December 3, 2009
Citation: Bekir, B., Lindenmayer, B., Nissen, S., Westra, P., Shaner, D.L., Brunk, G. 2009. Absorption and Translocation of Aminocyclopyrachlor and Aminocyclopyrachlor Methyl Ester in Canada Thistle (Cirsium arvense). Weed Science. 58:96-102.

Interpretive Summary: The management of invasive weeds is extremely important for natural areas in the U.S. A new herbicide, aminocyclopyrachlor, is being registered to control many of the most pernicious broadleaf invasive weeds including Canada thistle, which is a very serious problem throughout the U.S. A study was conducted to determine the effect of formulations on the translocation of aminocyclopyrachlor in Canada thistle. The results showed that both the free acid and the methyl ester formulations of aminocyclopyrachlor were absorbed by and translocated in Canada thistle and that methylated seed oil is the best adjuvant for maximum uptake and translocation. These results will aid in the usefulness of this new herbicide by minimizing the amount of herbicide needed to control invasive weeds.

Technical Abstract: Laboratory studies were conducted using radiolabeled aminocyclopyrachlor (DPX-MAT28) and its methyl ester (DPX-KJM44) to determine the 1) importance of surfactants for herbicide absorption 2) translocation patterns of the two formulations and 3) rate that aminocyclopyrachlor methyl ester was metabolized to the free acid in Canada thistle. Canada thistle plants were grown from root cuttings and treated in the rosette growth stage. The effect of different surfactants on absorption was determined by treating individual leaves with formulated herbicide plus radiolabeled herbicide alone or with MSO, COC or NIS with and without UAN and AMS. Plants were harvested after 96 HAT. For absorption and translocation experiments plants were over-sprayed with aminocyclopyrachlor or its methyl ester at a rate of 0.14 kg/ha in combination with 1% MSO. Formulated herbicide plus radiolabeled herbicide was then applied to a protected leaf and plants were harvested 24 to 192 hours after treatment (HAT.) Individual plant parts were oxidized and radioactivity was determined. Metabolism of aminocyclopyrachlor methyl ester to the free acid was determined 2, 6, and 24 HAT and all above ground biomass was analyzed by HPLC to establish the ratio of methyl ester to free acid. MSO alone resulted in the highest absorption for both herbicide formulations compared to no surfactant. Significantly more aminocyclopyrachlor methyl ester was absorbed compared to the free acid and this was reflected in greater above ground translocation for the methyl ester. Both formulations had similar amounts of translocation to the root; 8.6% for the methyl ester compared to 6.2% for the free acid. Approximately 80% of the methyl ester was converted to the free acid 6 HAT. Based on this conversion rate, the herbicide would appear to translocate as the free acid.