Farmers recorded one of the highest surface water readings ever for thiobencarb in the Colusa basin last year, a situation that posed a drinking water issue for the city of Sacramento downstream.
The herbicide gives the water a muddy taste. While the reading dropped two days later, it has prompted a deeper discussion on the issue with the city, according to California Rice Commission President and CEO Tim Johnson, who spoke Monday at the annual conference of the California Association of Pest Control Advisors (CAPCA).
The basin has also experienced bumps in pyrethroid detections. That triggered a new program under the regional water board for reducing the impacts—at significant costs to the industry, said Johnson. He cautioned PCAs operating in the area to expect to discuss this with the Rice Commission as well as agricultural commissioners and the Department of Pesticide Regulation.
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By the way: Nitrates are not just a San Joaquin Valley problem. Yolo County is grappling with a spike in nitrate contamination in the groundwater, explained Johnson. The state began tackling nitrates in Priority 1 basins—mostly in the San Joaquin Valley—after launching the CV-SALTS program in 2019. The attention will shift to Priority 2 areas starting in January.
Water dischargers in the area will have to reduce their nitrate load over a 30-year timeline. That includes packing and processing facilities, the city of Davis, UC Davis and all growers—except for rice. According to the commission, the anaerobic nature of rice production limits the conversion of fertilizer into nitrate and the water does not easily penetrate the heavy clay soils.
