Cause & Control of Rice



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Project Leader and Principal UC Investigators

Robert K. Webster, professor, Department of Plant Pathology, University of California, Davis

Nicole Cintas, Research Associate, Department of Plant Pathology, University of California, Davis

Chris Greer, Research Associate, Department of Plant Pathology, University of California, Davis

The major goal of this ongoing project is to improve the understanding of rice diseases that occur in California and to develop methods for their control. The relationship between alternative rice residue management and the epidemiology of rice diseases is also a major focus. Stem rot and aggregate sheath spot are the major diseases under study. A separate project detailed elsewhere in this report centers on blast disease. Progress is summarized below.

Residue management trials

Research is continuing on alternative residue management practices at one site in Colusa County and a second at the Rice Experiment Station (Butte County). Practices under study include incorporation, rolling, removal and burning under winter flooded and unflooded conditions.

Disease.jpg (172012 bytes)After five years at the Colusa site, winter flooding continues to show a beneficial impact on stem rot incidence. Incidence of the stem rot-causing organism or ˘sclerotia÷ have been consistently lowest in winter-flood main plots. Total sclerotia per gram of seedbed soil has decreased each year of the study. Conversely, the total number of sclerotia and viable sclerotia per gram soil were significantly greater each year in the winter unflooded main plots.

As might be expected, the lowest number of sclerotia continue to be observed on the burned plots. In 1998 the ˘bale and remove÷ and the rolled treatments had significantly more stem rot than the incorporated plots. Also, the viability of the sclerotia on the burned plots was half that of the other treatments. Yields have continued to be highest on the winter-flooded main plots throughout the study.

Aggregate sheath spot (AGSS) has gradually increased at the Colusa site in all treatments, with the greatest increases on the unflooded main plots. Overall the AGSS infection and lowest inoculum levels have been on the winter-flooded, burned treatments.

After four years the Butte County site continues to produce inconsistent results. Stem rot disease levels are lowest on the burned treatments at this site. Also, AGSS levels are considerably higher at the Butte site, where winter flooding appears to favor its occurrence.

Fungicide Evaluations

Field tests of the fungicide Quadris show that with proper rate and timing, it reduces AGSS. In one trial on M-202 a single application 65 days after planting resulted in an 800 pound increase in yield. The treatment did not, however, minimize stem rot. Additional study on the benefits and timing of Quadris are needed, particularly in relationship to control of both AGSS and blast.

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