Field tests in 1966 and 1967 have confirmed initial reports from the Rice Experiment Station, Biggs, that chemical control of submersed aquatic weeds frequently results in substantial increases in rice yield. Promising materials for this purpose are TD294, Hydrothal 191, and chloroxuron. Injury to the seedling rice was the least when these chemicals were applied about 35 days after flooding and seeding. More work is needed to determine precisely how long riceland-treated water must be held to control the submersed weeds most effectively while also eliminating any possible hazard to wildlife, including fish. It should also be determined whether the yield increases result from decreased weed competition or from fertilization provided by the killed submersed weeds (which soon decay, releasing the organically bound plant nutrients).

This is a progress report on cooperative investigations by the departments of Botany and Agronomy of the University of California, Davis, the Agricultural Extension Service, and the California Cooperative Rice Research Foundation, Biggs.