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Title: Aminopyralid binds more tightly to soil than clopyralid

item Bukun, Bekir
item Shaner, Dale
item Nissen, Scott
item Westra, Phil
item Brunk, Galen

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2010
Publication Date: 3/2/2010
Citation: Bukun, B., Shaner, D.L., Nissen, S., Westra, P., Brunk, G. 2010. Aminopyralid binds more tightly to soil than clopyralid. Weed Science. 58:473-477.

Interpretive Summary: Aminopyralid is a new herbicide for use in non-cropland areas for the control of invasive weeds. Aminopyralid is closely related to clopyralid, a herbicide that has been used for decades. This study was done to compare the soil binding and movement of aminopyralid with clopyralid. Aminopyralid bound more tightly to soil and moved less on soil thin layer plates compared to clopyralid. The results suggest that aminopyralid will leach less in soil compared to clopyralid.

Technical Abstract: Laboratory studies were conducted to compare the soil adsorption of aminopyralid and clopyralid using batch slurry and centrifugation assays. The calculated soil binding constants for both herbicides varied between the two techniques, but the centrifugation assay had a lower coefficient of variation compared to the batch slurry assay. These results suggest that the centrifugation assay is a better procedure for herbicides that do not bind tightly to soil. Amiopyralid bound more tightly than clopyralid to six of the eight soils tested. Adsorption Kd values ranged from 0.083 to 0.364 for clopyralid and 0.106 to 0.697 for aminopyralid. Pearson correlation analysis showed that the binding of both herbicides was highly correlated to soil organic matter and texture but not to soil pH. Aminopyralid, on average, did not move as much on soil thin layer plates (Rf=0.82) compared to clopyralid (Rf=0.91) although both herbicides were highly mobile. These results suggest that aminopyralid will have a lower leaching potential than clopyralid.