|Abit, Mary Joy -|
|Rainbolt, Christine -|
|O"connell, Neil -|
|Faber, Ben -|
|Hanson, Bradley -|
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 2012
Publication Date: October 1, 2012
Citation: Abit, M., Shaner, D.L., Krutz, L.J., Rainbolt, C., O"Connell, N., Faber, B., Hanson, B. 2012. Assessing Simazine Degradation Patterns in California Citrus Orchards with Different Simazine Use Histories. Pest Management Science. Interpretive Summary: Simazine is a commonly used herbicide to control weeds in perennial tree and vine crops. However, growers have noticed that simazine, in some cases, is no longer providing the length of weed control that it once did. It is known from previous research that extended use of a triazine can result in an increase in the soil microbes that can rapidly metabolize the herbicide. In this research soil samples were taken from a number of orchards with varying histories of simazine use. Simazine degraded two- to three-fold more rapidly in soils taken from orchards in northern California with a history of simazine use compared to orchards where the herbicide had not been used. However there was no correlation between simazine degradation rates and herbicide use history in soils taken from orchards in southern California. These results indicate that repeated simazine use in can lead to enhanced simazine degradation due to microbial activity but soil type and long term cropping factors can affect the persistence and distribution of herbicide degrading microbial populations in California orchards.
Technical Abstract: Simazine is commonly used to control broadleaf weeds and annual grasses in perennial tree and vine crops because of its relatively low cost and long residual activity. Simazine may be subject to enhanced biodegradation in some areas which can result in decreased herbicide half-life and reduced residual weed control. Laboratory studies were conducted to determine if rapid simazine degradation occurs in California citrus orchards and if degradation rates can be directly correlated to simazine use history. In the Central Valley, simazine degradation curves clearly indicate that simazine degradation rate is more rapid in soils with a history of simazine use (adapted) compared to soils with no recent use (non-adapted). In these soils, dissipation of simazine was two- to three-fold greater in adapted compared with the non-adapted soils. However, in southern California, simazine dissipation and mineralization were not substantially different among soils with different simazine use histories. Results showed that repeated simazine use in California orchards can lead to more rapid degradation of the herbicide. The mineralization assays verify that the enhanced simazine degradation is due to microbial activity. However, soil type and long-term cropping factors can affect persistence and distribution of herbicide degrading microbial populations in California orchards.