The Rice Research Board therefore provides support funds annually for rice disease research to the UC Davis Department of Plant Pathology.

The 1975 research program had the following objectives:

1. Analyze disease severity to generate a program for predicting severity and yield losses (11 different locations).
2. Develop methods for screening varieties for stem rot resistance in laboratory and greenhouse trials at Davis.
3. Determine the epidemiology of stem rot and the biology of Sclerotium oryzae; the effects of cultural practices on inoculum levels, inoculum production, and survival; and the predisposition effects of herbicides, fertilizers, and stand density. Conduct laboratory and greenhouse experiments at Davis; field trials at Davis and Butte Co.
4. Develop chemical control of stem rot. Conduct field trials at five locations (Davis and Butte Co.), and laboratory and greenhouse studies (Davis). Make residue analyses throughout the season; all crop samples to be shipped to Kansas City and processed by Thompson Hayward Chemical Company, to speed registration of promising chemicals for stem rot control.
5. Conduct additional trials with combinations of fungicides to replace Difolatan as seed treatments. Direct field trials in Butte and Yolo Counties, greenhouse and laboratory experiments at Davis.

 

UCD plant pathologist Dr. R. K. Webster shows data at field day that controlling rice stem rot with a single application of Du-ter (costing $9.00 per acre applied) increased rice yield by 500 pounds per acre.

CONCISE SUMMARY OF CURRENT RICE DISEASE RESEARCH:

Positive correlations found among stem rot severity, yield losses, and carry-over inoculum levels allow accurate prediction of disease losses under continuous rice culture. These will facilitate cultural decisions on burning, tillage methods, and use of fungicides. Studies are under way to evaluate various straw disposal systems and effects on stem rot incidence.

Proper timing and rate of herbicide applications help minimize losses to stem rot.

þ A fungicide, triphenyletin hydroxide (Du-ter), will control stem rot (where it is a problem) and increase rice yield up to 13% with a single application of 1 lb/A at midtillering. Total cost of the chemical and application in 1975 was about $9.00 per acre. Registration for use on rice has been applied for, and will likely be approved by 1977.

Seed-treatment fungicides have been identified to replace Difolatan. Difolatan has consistently proven effective for the purpose but standby alternatives are reassuring to have.

Studies continue on the biology of S. oryzae. Several leads have been found that promise biological control.