Evaluation of Alternative
Methods for Managing Algae
in California Rice - 2005



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Project Leader and Principal UC Investigators

David Spencer, ecologist, USDA/ARS Exotic and Invasive Weeds Research Unit, Dept. of Plant Sciences, UC Davis




Previous work on filamentous algae in California rice fields examined the nature and abundance of the species present. Research in 2005 examined different methods of reducing the green and blue-green algae dominant in California rice fields. This project also compared rice field soil copper with levels in natural wetlands.

Algae control

Researchers conducted algae control experiments in California rice fields and at UC Davis. They examined four copper-containing products, a chloride-based product and a hydrogen peroxide-based product. Although one of the copper products reduced chlorophyll content of the blue-green algae Nostoc in the laboratory, none of the products consistently reduced Nostoc levels under field conditions.

Copper levels

"Results from several outdoor and field experiments indicated that none of the products examined significantly and consistently reduced growth of algae collected from CA rice fields."

Soil samples were taken from rice fields and natural wetland areas across a wide geographic area of Northern California. The level of total copper in rice field soils was 16 percent higher than in wetland soil samples. Additionally, a greater percentage of copper was present in a biologically available form in rice field soils than in wetland soils.

"Black algae" seen here at 40 times magnification has become more prevalent in grower fields.

Projections made in 1994 indicated that total copper in the soil would increase by 1.1 parts per million per year with each application of 10 pounds/acre of bluestone. Growers typically apply this amount each year to control algae and tadpole shrimp. Levels of total copper in 2004 and 2005 were close to expected levels when compared to the levels measured in rice fields in 1994. Total copper remains below levels expected to affect rice yields.


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