UC Davis

The predominant method of rice crop establishment in California is water seeding (WS), wherein pre-imbibed seed is flown by aircraft into permanently-flooded basins, where the seed settle and peg-down roots. This system encourages aquatic species and sedges, as well as the development of flood-adapted grass populations. Herbicides are the primary means of weed control in WS rice, but the permanently-flooded culture does not permit a large palette of available herbicides. Constant use of few herbicides on a small spectrum of locally-adapted weed ecotypes has resulted in widespread herbicide resistance in the region. Alternative stand establishment methods may permit the use of herbicide modes of action that are not normally available in WS rice, and for which resistance has not developed in the local rice-weed populations. Two such methods are the stale-seedbed, and drill-seeding. We hypothesized that drilling dry rice seed below the zone of active weed germination and emergence will delay rice stand emergence until after the first 1-2 flushes of weeds have emerged. This novel stale-drill method would permit the use of a broadspectrum herbicide as a postplant-burndown (PPB) treatment to safely control emerged weeds without causing stand injury or yield loss. We also hypothesized that California rice cultivars possessed sufficient vigor to emerge rapidly and evenly from soil depths exceeding 2 cm, with minimal stand reductions. Field and greenhouse experiments were carried out to determine the feasibility of the stale-drill method, by assessing herbicide protocols, treatment timing, field scouting, water management, the relative vigor of California rice cultivars, and crop responses of cultivars to seeding depths of up to 6 cm. Field experiments confirmed that using glyphosate as a PPB treatment was able to control more than half of a season’s weeds, but weather and planting date had significant effects on the emergence of cultivar M-206. Greenhouse experiments identified M-205 and M-209 as cultivars with superior vigor, as seen in rates of belowground elongation, emergence, and early-season growth and development. Further field studies confirmed that stale-drilled M-206 and M-209 can emerge evenly from depths up to 6 cm, and return yields competitive with local averages for WS rice. Planting date had a significant effect on M-209 heading, grain filling, and grain yield. As a whole, this research serves as a successful proof of concept for the stale-drill method for rice stand establishment, and adds to the growing body of knowledge of integrated weed management in mechanized crops.