Interview with Dr Eric Westra

Posted Wed, Apr, 22,2015

This author interview is by Dr Eric Westra, of Colorado State University. Dr Westra's full paper, Evaluation of Sorption Coefficients for Pyroxasulfone, s-Metolachlor and Dimethenamid-p, is available for download in Air, Soil and Water Research.

Please summarize for readers the content of your article.

This article evaluates the sorption coefficients for a relatively newer pre-emergent herbicide pyroxasulfone, and compares relative soil adsorption to the industry standards s-metolachlor and dimethenamid-p. Soil adsorption for all three compounds were evaluated over 25 different soil types collected from across the US in order to evaluated what chemical and physical soil characteristics influence soil adsorption. Relative order of soil adsorption across 25 different soil types was evaluated for all three herbicides, and correlations to soil characteristics were conducted to see what soil properties most influence herbicide soil adsorption.

How did you come to be involved in your area of study?

I became involved in this area of study when working on research for my master thesis. I obtained my undergraduate degree in Soil and Crop Sciences from Colorado State University and when I continued on for my M.S. degree, I had to opportunity to work on basic soil interactions for a new pre-emergent herbicide pyroxasulfone.

What was previously known about the topic of your article?

Soil adsorption had been evaluated for s-metolachlor, but there was none, or limited information on soil adsorption for pyroxasulfone or even dimethenamid-P. S-Metolachlor has been used for many years, and both growers and applicators have developed information on how this herbicide works under different field conditions (i.e. soil types) based on experience and soil sorption coefficients.

How has your work in this area advanced understanding of the topic?

This research on sorption coefficients for pyroxasulfone, and relative comparisons to s-metolachlor and dimethenamid-P will provide growers and applicators information on relative soil adsorption in order to avoid applications that result in reduced weed control efficacy (to low of rates), or potential leaching (to high of rates) based on the soil types in which pyroxasulfone will be applied to. Evaluating how pyroxasulfone compares to s-metolachlor over multiple soil types with different chemical and physical characteristics can provide relative insight into how pyroxasulfone will behave when applied in the field.

What do you regard as being the most important aspect of the results reported in the article?

Water solubility of these three pesticides cannot be used to determine the relative order of soil adsorption. Pyroxasulfone has the lowest water solubility out of these three pesticides, however it bound the least across all soil types. Pesticide water solubility values can typically be used to predict soil adsorption, and subsequent amounts of herbicide available for plant uptake and weed control. Pyroxasulfone is a unique compound in that it has a low water solubility as well as low relative soil sorption coefficients where it is available for plant uptake and weed control. Low soil adsorption could explain the similar weed control efficacies even though pyroxasulfone is applied at a much lower use rate compared to dimethenamid-p and s-metolachlor.

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