Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2008
Publication Date: 5/12/2008
Citation: Krutz, L.J., Burke, I.C., Reddy, K.N., Zablotowicz, R.M. 2008. Evidence for Cross-Adaptation between s-triazine herbicides resulting in reduced efficacy under field conditions. Pest Management Science. Online DOI 10.1002/PS.169. Interpretive Summary: A rapid loss of herbicides such as atrazine in soil by bacteria using the compound as a nutrient source is called “enhanced degradation”. This can be a problem for growers if enhanced degradation reduces weed control. This may also result in the rapid loss of similar compounds by a process called “cross-adaptation”. This fields study evaluated if 1) simazine is cross-adapted with atrazine; and 2) if a rapid loss of simazine reduces control of the weed, prickly sida. Field studies shown that simazine’s half-life in soil is reduced 70% in atrazine-adapted soils compared to non-adapted soils. Laboratory studies confirmed that the rapid loss of simazine in atrazine-adapted soils is due to cross-adaptation. Despite more rapid dissipation of simazine in atrazine adapted soils, prickly sida control with simazine was only slightly lower in adapted than non-adapted soils and corn yield was similar in both fields. Results from this study indicate that 1) simazine is cross-adapted with atrazine; 2) a loss of weed control with simazine was documented in atrazine adapted soils under field conditions.
Technical Abstract: Soils exhibiting enhanced atrazine degradation may be cross-adapted with other triazine herbicides resulting in reduced residual weed control. The objectives of this study were to 1) determine field persistence of simazine in atrazine adapted and non-adapted soils; 2) compare mineralization of ring-labeled 14C-simazine and 14C-atrazine between adapted and non-adapted soils; and 3) compare prickly sida control with simazine in adapted and non-adapted soils. Pooled over two pre-emergent application dates, simazine field persistence was 1.4-fold lower in adapted than non-adapted soils. For both simazine and atrazine, the mineralization data indicated the lag phase was 4.3-fold lower and the mineralization rate constant 4.0-fold higher in adapted than non-adapted soil. Mineralization data confirm that reduced field persistence of simazine is due to cross adaptation between triazine herbicides. However, despite reduced persistence of simazine in adapted soils, only a slight reduction in prickly sida control occurred, and no in-season yield loss was observed. Results from this study indicate 1) simazine is cross-adapted with atrazine; 2) prickly sida control with simazine is reduced in atrazine adapted soils; but 3) the reduction of residual weed control with simazine does not affect yield.