|Evaluation of Alternative
Methods for Managing Algae
in California - 2007
Project Leader and Principal Investigators
David Spencer,ecologist, USDA/ARS, Exotic and Invasive Weeds Research Unit, Dept. of Plant Sciences, UC Davis
Research continued in 2007 on methods to control filamentous algae in
California rice fields. Laboratory and field studies focused on zinc,
copper and phosphorous, as well as herbicides.
Zinc and copper studies
Researchers tested several ways to kill or reduce Nostoc, a problematic blue-green algae increasingly present in some rice fields.
The highest concentrations from a commercially available zinc sulfate product reduced this algae by about 50 percent. This is consistent with findings from the previous two years and supports anecdotal evidence that fields treated with 50 pounds/acre zinc sulfate fertilizer often have less severe algae problems.
Rice straw was observed to have a binding capacity with copper and could affect the efficacy of copper sulfate treatments. The copper-containing algaecide “Formula 30” reduced algae biomass in another experiment.
Experiments continued with the ALS-inhibiting herbicides bispyribac, imazamox, and penoxsulam on additional algal species. Results indicated that one of five species of green algae was affected; three of five planktonic blue-greens were affected; and neither of the two mat-forming blue-green species was affected. Some algae species recovered after herbicide exposure.
Experiments with a mix of herbicides bensulfuron methyl and carfentrazone ethyl did not significantly reduce Nostoc abundance. However, researchers observed a 12% decrease in Nostoc growth rate at the highest levels of this herbicide combination.
Field tests with sodium carbonate peroxydydrate, which releases hydrogen peroxide, had no significant effect, confirming findings from previous, smaller scale studies.
One approach to managing excessive algal growth is to alter environmental conditions that support its growth, such as the availability of phosphorous. Previous experiments showed that burying phosphorous fertilizer in soil reduced phosphorous levels in overlying irrigation water. An experiment in 2007 showed that in a field where phosphorous fertilizer had not been incorporated into soil, phosphate levels increased up to five times that of incoming water moving onto a field. This provides additional strong evidence that incorporating phosphorous fertilizer would lead to reduced phosphate levels in rice field water and subsequently reduce algae growth, especially Nostoc.