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Reducing Pesticide Potential for Leaching
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Significant leaching normally only occurs to pesticides that are weakly retained by soil and that are relatively stable in the environment. In California, the most "problematic" pesticides are pre-emergence herbicides. Because these herbicides are usually applied before weed emergence, they have to "stick" around in soil for sometime to achieve the function of weed control. Be design, these pesticides are also relatively mobile in soil so that they can be distributed in the surface soil layer and can be absorbed or come in contact with weed seeds or seedlings.
In many cases, pesticide movement to groundwater can be prevented by modifying common practices. Because water is the carrier for pesticides in soil, practices centering around irrigation management are usually effective in reducing pesticide downward movement. When this effort fails, it is advisable to use an alternative product with different properties. You may use PesticideWise to search for products that will have a lower leaching potential for your site.
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1) Irrigation rates:Reduce irrigation rates so that less water is percolated into the soil. You can achieve this by simply irrigating less. Over-irrigation is a common practice. Over irrigation is often used to compensate for poor irrigation efficiency due to faulty irrigation systems or non-uniform irrigation patterns.
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2) Irrigation systems:Change irrigation systems or habits to avoid water ponding (or flooding) on the surface.
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3) Irrigation timing:Schedule irrigation events in a way to avoid excessive water infiltration right after pesticide application.
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4) Rain storms:Avoid timing pesticide application with major rain events, because excessive rainfall will drive pesticide deeper into the soil.
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5) Collection ponds:Ponds used for tail water collection can become a source for pesticide leaching at locations with shallow water table. Improve pond construction or avoid keeping water in the pond for a prolonged time period.
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6) Alternative pesticides:Some pesticides are by design more vulnerable to leaching than other pesticides. If possible, switch to products that are capable of the same pest/weed control but with reduced potential for groundwater pollution. You may search through Pesticide Manager to search for products that have a lower leaching potential for you. For pesticides currently registered for use in California, check at California Department of Pesticide Regulation
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7) IPM:Adopt Integrated Pest Management practices to reduce pesticide use and risks. Check out UC IPM
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