Disease Control - 80



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Project Leader and Principal UC Investigators

Robert K. Webster, Dept. of Plant Pathology, UC Davis


Disease Management Alternatives

Rice residue infested with S. oryzae or the sheath blight pathogen is an ideal medium for inoculum level increases when it overwinters on the surface or is poorly incorporated into the soil. Microorganisms and chemicals that prohibit this build up have been identified and are being field tested.

The pathogen that causes sheath blight was found to be widely distributed in rice-producing areas of California. It differs in host range, biology, and aggressiveness from the sheath blight pathogen in Southern states. The disease cycle of sheath blight appears to be similar to that of stem rot. Preliminary results indicate that severity of sheath blight is affected by varieties grown and manner of residue disposal.

Effects of Cultural Practices on Diseases

The commercial use of Duter for stem rot control is still being held up by federal requirements. Promising new fungicides for the control of both stem rot and sheath blight have been identified. Treatment of seed beds and/or water for stem rot is promising but needs further study.

Stem rot severity is enhanced by excess nitrogen fertilization. A similar correlation for sheath blight was not observed in this year's trial.

Current seed treatment chemicals were at least as effective as new formulations being offered.

A comparison of the effects of MCPA and Basagran for predisposition to stem rot and sheath blight in a large field trial revealed no significant differences between application of the two herbicides and subsequent disease severity or yield.

A study to determine the effects of alternate cropping on rice disease epidemiology has been initiated. Beginning levels of disease were determined this year. The study will be continued to determine effects of alternate cropping on stem rot and sheath blight disease severity.

Biological Control of Stem Rot

Basic genetic studies at UCD by USDA's Dr. J. Neil Rutger and UC plant pathologist Dr. Robert K. Webster have provided new sources of stem rot germplasm resistance for use by plant breeders at the Rice Experiment Station. Progress on identifying and transferring resistance to stem rot from wild species of rice to California varieties is encouraging.


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