|Cause and Control of
Project Leader and Principal UC Investigators
Robert K. Webster - Professor, Department of Plant Pathology UC Davis
Nicole Cintas - Research Associate Department of Plant Pathology, UC Davis
Chris Greer - Research Associate Department of Plant Pathology, UC Davis
The major goal of this ongoing project is to
further an understanding of the biology of rice diseases occurring in California and to
develop methods for their control. Two factors are currently driving its research agenda.
First, the legislatively mandated phase down in open field burning appears to increasing
the severity of stem rot and aggregate sheath spot, thus underscoring the importance of
alternative residue management strategies. Second, the appearance of rice blast in 1996
has compelled plant pathologists to expand their efforts into a whole new area of research
to under- stand the nature of this potentially devastating disease and to develop methods
for its control The narrative below summarizes progress in research into these diseases.
Developments On Blast Disease
Plant pathologists have devoted a substantial amount of time and energy attempting to learn more about the rice blast infestation. Here's a quick run-down of what they are finding:
Residue Management Trials
Research is continuing on how various residue management practices affect aggregate sheath spot and stem rot at an on-farm site in Colusa County and at the Rice Experiment Station. Alternative practices in four-year-old study include incorporation, rolling, removal and burning under winter flooded and unflooded conditions.
At the Colusa site, winter flooding appears to be having a beneficial impact on stem rot incidence. Evidence of the stem rot-causing organism or "sclerotia" was lowest on winter flooded main plots, while they've been increasing each year on the unflooded plots. Not surprisingly, the fewest number of viable scierotia were observed on the burned treatments. Yields were also highest in the winter flooded main plots in the first three years but were considerably higher in all treatments in 1997. Researchers attribute this to lower overall disease levels, a change in harvest method and a generally favorable year for rice development.
Aggregate Sheath Spot has gradually increased at the Colusa site in all treatments, with the greatest increases in unflooded main plots. Overall, the lowest Aggregate Sheath Spot levels have been in the winter-flooded, burned subplot treatments.
Observations from the Butte County site reveal a pattern somewhat contra- dictory to those from the Colusa site. Aggregate Sheath Spot levels are considerably higher at the Butte site, suggesting that winter flooding favors the survival and occurrence of this disease. There is some evidence that yield differences in the various sub-plots may be due to potassium nutrition differences between the residue and treatments. Also, soil types differ between the two sites and the initial level of disease was much higher at the Butte site than at the Colusa site.
Field tests were established at two sites in Glenn County and one in Sutter County to evaluate rates and timing of application for fungicides to control Stem Rot and Aggregate Sheath Spot. Quadris proved to be the most promising, with a 1,400 pound increase over the control in one trial. Another trial was severely infected with blast, which showed that two early applications of the fungicide did not reduce either leaf or neck blast. Plant pathologists emphasize that fungicides should be used as a protectorant of vulnerable neck nodes during heading and that attempts to control leaf blast with multiple, earlier applications are not only costly but futile.
Predicting Disuse Levels
Under the provisions of the burning phasedown, growers can be allowed to burn fields threatened by severe infestations of rice diseases. The challenge has been to find a reliable method to predict disease levels early enough to do something about it.
Based on two years worth of stem rot severity ratings taken during the month of August, plant pathologists have developed a reliable method of predicting current season yield loss and potential future stem rot damage in next year's crop. From these ratings, regulatory decisions could be made in time to allow burning in the fall.
Plant pathologists continue to evaluate rice from the National Small Grains germplasm collection for sources of improved resistance to Stem Pot and Aggregate Sheath Spot. Plants are scored for the presence of both diseases throughout the growing season. Of more than 6,000 entries, 29 have potential for use as future parents in plant breeding efforts.