Cause and Control of Rice



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Project Leader and Principal UC Investigators

Robert K. Webster, professor, Department of Plant Pathology, UC Davis


disease.JPG (13589 bytes)The major goals of this project are to gain an improved understanding of the diseases that affect rice grown in California and to develop methods that minimize their damage to the rice crop. Emphasis is currently on stem rot, aggregate sheath spot, blast and Bakanae. Control methods under study include cultural practices that affect occurrence and severity of diseases and the potential use of fungicides. Details of research in these areas are below.

Blast Monitoring

Rice blast disease was “of little consequence” in the 2001 California rice crop. It was not observed until mid-August and then only in a few fields where it has been known to occur in previous years.

Thus far the disease has been found in Colusa, Glenn, Sutter, Butte and Yuba counties. DNA fingerprinting of field samples taken from 2000 and 2001 has identified only one race of Pyicularia oryzae, the organism that causes blast disease.

Plant pathologists urge continued caution when possible by using disease-free seed sources and avoiding unintended transport of disease organisms on equipment that may have residue or dust containing the blast pathogen.

Fungicide Trials

Disease2.JPG (22540 bytes)Trials on M-202 and M-205 to determine optimum application timing for the fungicide Quadris to control Aggregate Sheath Spot (AGSS) and Stem Rot (SR) showed no significant increase in yield. The only significant increase in quality—improved head rice—occurred when Quadris was applied to M-202 at 70 days after planting.

Combined with results from previous years, this supports the conclusion that fungicide applications should only be used in cases of known high AGSS incidence or if it appears there may be problems with neck blast during the present crop season.

Growers should also determine whether increases in quality (head and total) are large enough to justify the cost of fungicide treatments.

Bakanae Disease

Scientists took a deeper look into the life cycle of California’s newest rice disease, Bakanae, first discovered in the state during 1999. The disease was described as widespread last year, occurring in Colusa, Butte, Glenn, Sutter and Yuba counties and also spreading to Yolo County for the first time in 2001.

Laboratory analysis showed that seedlings may become infected from the pathogen Fusarium moniliforme Sheld in soil or residue but all available information indicates the disease is primarily seed born. The pathogen is abundant in residue of harvested plants, providing the main source for infestation of seed. Previous studies have shown that the pathogen is primarily a surface contaminant of seed.

Initial greenhouse studies showed that treatment of infested seed with the fungicide Maxim resulted in a significant reduction of diseased plants. Further study, especially field tests, are needed to determine the effectiveness of fungicide seed treatments under field conditions, possible phytotoxicity resulting in inhibition of root elongation, and potential impact on stand establishment.


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