Education For
Environmental Responsibility

Vegetated Ditch Study

This study was part of a larger Pesticide Research and Investigation of Source and Mitigation Grant Program (PRISM) project designed to demonstrate the use of several best management practices that may reduce chlorpyrifos loading in return water from irrigated crops in the Orestimba Creek region of the San Joaquin River watershed.

Typically, irrigation occurs in this region throughout the summer, coinciding with periods of pesticide application. Irrigation water moving across a recently sprayed field can mobilize chlorpyrifos, which is relatively water soluble, and move it to conveyance ditches at the edge of the field where it is then drained to tailwater ponds or discharged into local surface waters.

Agricultural irrigation return ditches in California are commonly dredged to remove as much vegetation as possible in order to maintain flow-carrying capacity. However, by allowing vegetation to remain within the ditch, thus slowing the flow rate and providing more time and potential for degradation, pesticide concentrations in runoff may be reduced. This study demonstrates a constructed, vegetated conveyance ditch as a potential management practice for reducing off-site movement of chlorpyrifos to surface water in irrigated alfalfa.

• Vegetated Ditch Study (PDF file)

• Vegetated Ditch Study (Slideshow)