Work continued for a second year on the development of an early warning system for the detection of rice blast disease by the private company FieldWise, Inc. An effective and reliable rice blast model is necessary to provide growers with a valuable management tool to decide when fungicide applications are warranted.

Scouting Report

With a concerted effort among an experienced group of about 20 PCAs and growers, fields were more closely scouted for rice blast throughout the season than in previous years. FieldWise provided instruction on identification of rice blast symptoms and the most efficient method of scouting the disease. Fields were checked at least twice a week in Glenn, Colusa, Butte, Sutter, Yuba, Yolo and Tehama counties. Each field with a suspected case of rice blast was visited within 24 hours to confirm or dismiss the presence of the disease. Information from FieldWise scouting reports and weather conditions was made available on the Web at http://www.fieldwise.com and also on the Syngenta Rice Disease hotline.

The first observation of rice blast during the 2001 season was made August 22 near Maxwell, a month later than in previous years. A second area of rice blast was reported October 8 in a Glenn County field between Willows and Maxwell. These were the only two confirmed sites with rice blast in 2001. Overall disease pressure appeared to be very low. Possible reasons for the low disease incidence include low inoculum levels or cool night temperatures during mid- to late season that may have provided less than optimal conditions for the disease.

Nine remote weather monitoring stations in rice fields are part of a larger network operated by the company and cover a large part of the Sacramento Valley. This network also collected information in tomatoes, grapes, walnuts and almonds. It provides data for daily updated weather forecasts and maps depicting the previous day’s weather conditions (maximum and minimum temperature, average relative humidity and precipitation).

Early detection is a key element in making informed pest management decisions. Results of this research indicate that monitoring rice blast with the help of a PCA and grower scouting program was useful in determining the extent of rice blast incidence in the Sacramento Valley. Much more ground was covered and fields were examined more closely than in previous years, yet the disease was observed in only two areas.

Model Development

Collection of another year of weather data has been instrumental in developing a model for rice blast prediction in California. This model relies on an evaluation of leaf wetness and temperature during the leaf wetness period to generate a daily rice blast disease index. The infection process requires an extended period of leaf wetness and is dependent upon temperature. These are the most important two factors in determining the likelihood of infection by the pathogen when spores are present.

Development of a rice blast model for California will assist in evaluating the risk of disease development as rice plants approach the heading stage. Just prior to heading is the critical time to decide if a fungicide application is warranted. Preliminary indications are that the modified model may be useful in predicting rice blast infection periods. Intense field scouting will still be required to determine if rice blast lesions are within a field or in surrounding fields that may provide inoculum when conditions are favorable for infection.