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Title: ENHANCED DEGRADATION OF ATRAZINE UNDER FIELD CONDITIONS CORRELATES WITH A LOSS OF WEED CONTROL IN THE GLASSHOUSE

Author
item Krutz, Larry
item Zablotowicz, Robert
item Reddy, Krishna
item Koger Iii, Clifford
item Weaver, Mark

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2006
Publication Date: 1/1/2007
Citation: Krutz, L.J., R.M. Zablotowicz, K.N. Reddy, C.H. Koger III, and M.A. Weaver. 2007. Enhanced degradation of atrazine under field conditions correlates with a loss of weed control in the glasshouse. Pest Management and Science 63:23-31. Krutz, L.J., R.M. Zablotowicz, K.N. Reddy, C.H. Koger III, and M.A. Weaver. 2007. Enhanced degradation of atrazine under field conditions correlates with loss of weed control in the greenhouse. Pest Management Science 63:23-31.

Interpretive Summary: Repeat applications of atrazine, one of the most widely used soil applied herbicides, to some soils may promote the development of a microbial population able to rapidly degrading the herbicide thereby reducing its herbicidal activity. This study describes the dissipation and herbicidal activity of atrazine in soil as a function of exposure history. Dissipation of atrazine was 2-fold greater in atrazine history soils compared to soil with no prior exposure to the herbicide. This resulted in a loss of residual weed control in atrazine history soils. This is the first study to link atrazine exposure history with enhanced degradation and reduced herbicidal activity. Producers, crop consultants, and chemical companies need to be aware that repeat applications of atrazine to soil may result in a enhanced degradation and a loss of residual weed control.

Technical Abstract: Enhanced degradation of atrazine has been reported in the literature indicating the potential for reduced residual weed control with this herbicide. Experiments were conducted to determine the field dissipation of atrazine in three cropping systems: continuous Zea mays L. (CC) receiving atrazine applications each year, Z. mays-Gossypium hirsutum L. rotation (CCR) receiving applications of atrazine once every two years, and a no atrazine history soil (NAH). Subsequent laboratory and greenhouse experiments were conducted with these soils to determine atrazine degradation, mineralization, and residual weed control. Field dissipation of atrazine followed first order kinetics, and calculated half-life values for atrazine combined over 2003 and 2005 increased in the order of CC (9 d) = CCR (10 d) < NAH (17 d). Greenhouse studies confirmed that the persistence of atrazine was approximately 2-fold greater in NAH compared to CC and CCR. Mineralization studies suggested that enhanced degradation of atrazine was due to rapid catabolism of the s-triazine ring. Efficacy studies revealed a loss of residual weed control in CC and CCR compared to NAH. These data indicate that under typical Mississippi Delta field conditions and agronomic practices, the persistence of atrazine may be reduced by at least 50% if the herbicide is applied more than once every 24-months. Moreover, in soils exhibiting enhanced degradation of atrazine, a loss of residual weed control is likely.