Research continued in 2008 on methods to control filamentous algae in California rice fields. Laboratory and field studies focused on the effects of water quality in rice fields and various algaecides on the growth of Nostoc, a problematic blue-green algae in some fields.

Rice field water quality

How water quality conditions affect the growth of Nostoc and the effectiveness of control measures was the objective of one area of research during 2008.

In a laboratory, scientists examined the growth of Nostoc under a range of sodium concentrations in water samples. Additional parameters tested included the algaecide Rice Cop 5, light levels, water temperature, and the presence of iron.

Highlights of this work on Nostoc show:

• The algaecide Rice Cop 5 significantly reduced algae photosynthetic activity and thus biomass production when applied at the maximum rate.

• Sodium does not appear to be a limiting growth factor.

• Warm water temperatures and low light similar to conditions during initial flooding and rice seeding are conducive to algae growth.

• Elevated levels of iron applied as ferrous sulfate significantly reduced algae biomass.

Phosphorous management

Phosphorous management is a key element in effective control of Nostoc. In 2008, a field study compared four different phosphate fertilizer applications:

• Phosphate applied 30 days after flooding

• Surface-applied liquid phosphate fertilizer, followed by a roller

• Phosphate fertilizer applied and soil incorporated during spring

• Phosphate fertilizer applied in the fall and incorporated into soil in spring

Algal biomass was lowest in field that received the 30-day, after-flooding treatment. These fields had 72 percent to 88 percent less algal biomass than fields receiving conventional phosphate application (surface-applied liquid phosphate followed by a roller). The results show that this treatment was clearly the most effective application method.