Submitted to: Pest Management Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2009
Publication Date: 2/2/2010
Citation: Krutz, L.J., Shaner, D.L., Weaver, M.A., Webb, R.M., Zablotowicz, R.M., Reddy, K.N., Huang, Y., Thomson, S.J. 2010. Agronomic and Environmental Implications of Enhanced s-Triazine Degradation. Pest Management Science. 66:461-481. Interpretive Summary: The way soil bacteria degrade s-triazine herbicides have changed, thereby requiring us to revaluate how these compounds behave in the environment. From an agronomic perspective, residual weed control in soils that have bacteria with this new metabolic ability will be 10-fold lower than what is traditionally expected. Moreover, from an environmental standpoint, if fate and transport models do not account for this altered metabolic pathway then off-site transport of s-triazine herbicides could be overestimated by 13-fold. We have developed an empirical model that predicts atrazine persistence in soil with bacteria able to rapidly degrade this herbicide. This empirical model could be used by weed scientists and modelers to better predict the behavior of atrazine in the environment.
Technical Abstract: Novel catabolic pathways enabling rapid detoxification of s-triazine herbicides have been elucidated and detected at a growing number of locations. Herein we describe the potential agronomic and environmental ramifications of these bacterial adaptations. The genes responsible for s-triazine mineralization by soil bacteria, i.e., atzABCDEF and trzNDF, occur in at least four bacterial phyla and are implicated in the development of enhanced degradation in agricultural soils from all continents except Antarctica. Enhanced degradation occurs in at least 9 crops and 6 crop rotation systems that rely on s-triazine herbicides for weed control and, with the exception of acidic soil conditions and s-triazine application frequency, adaptation of the microbial population is independent of soil physiochemical properties and cultural management practices. From an agronomic perspective, residual weed control in s-triazine adapted soils could be reduced by 10-fold relative to non-adapted soils. Moreover, in adapted soils, the off-site loss of total s-triazine residues could be overestimated by 13-fold if altered persistence estimates and metabolic pathways are not reflected in fate and transport models. Empirical models requiring soil pH and s-triazine use history as input parameters more accurately predict atrazine persistence than historical estimates. Empirical models may allow practitioners to adjust weed control strategies and model input values when warranted.