NEWS: For Immediate Release

Steven C. Scardaci, U.C. Farm Advisor

March 27, 1997

Rice Blast Update

Many rice growers have expressed concern about the possible reoccurrence of the blast disease in 1997. UC rice experts say that last summers warm-humid nights were favorable for disease development, but are hopeful that a return to more normal weather will be less favorable for the disease. Only time will tell.

Growers are also concerned that blast infected seed may initiate the disease in their fields. While it is true that the blast fungus may overwinter in seed and can be transmitted to seedlings, it is less likely to occur under the water-seeded system that most area growers use. According to UC Farm Advisor Steven Scardaci, previous research in the Southern U.S. has shown that planting seed in water almost completely controls seedling infection from seed. Studies conducted in the laboratory using three stimulated planting methods (drill-seeding, water-seeding and soil surface seeding) showed that drill-seeding allowed transmission of blast from seed to seedlings, but that water-seeding did not. They did show, however, that seeding rice on the surface of moist soil, as may happen on levees or high spots of water-seeded fields, also results in seed transmission of the disease. They also showed that drainage of water sooner than 2 days after water-seeding can allow disease transmission to seedlings.

Even though we feel that the threat of getting blast from seed is minimal, UC experts are encouraging the use of clean seed, whenever possible. We have also encouraged seed sampling and testing to identify and avoid the use of blast infested seed. This winter several rice seed suppliers submitted seed samples to the Department of Plant Pathology at the University of California at Davis for blast testing. A total of 108 samples were tested with nearly 90% of the samples testing negative for the blast fungus. Most of the positive samples had very low levels (0.25-0.50%) of the fungus in the seed. The highest level was 2.0%. These results indicate that blast is present in a few California rice seed lots, but at very low levels. Since this study did not include all California rice seed lots it can only provide some indication of the blast/seed situation.

This winter we had hoped that a sodium hypochlorite (chlorox-type products) seed soak would control blast in rice seed. However, studies conducted in the Department of Plant Pathology at UC Davis showed that the concentration of sodium hypochlorite necessary to control the blast fungus also caused significant reductions in rice germination and seedling vigor. It was concluded that such a seed soak would do more harm that good.

It should be pointed out that even though planting clean seed may help control the disease, fields may still become infected from airborne spore sources. Also, planting blast infected seed does not necessarily mean that a field will become infected.

The Rice Blast Task Force has issued a policy statement on blast as follows. Seed samples tested to date from the blast infested areas in 1996 indicate that the amount of infestation in California seed is very low and probably an insignificant threat to water-seeded rice. Nevertheless, the Task Force recommends that all rice seed suppliers voluntarily submit seed samples to laboratories using acceptable protocol to test for rice blast in seed supplies and that they voluntarily provide information about test results to seed purchasers. Further, the Task Force recommends that information about proper protocol for rice blast testing be made available to rice seed suppliers. The Task Force supports and endorses the University of California Extension publication entitled, "Rice Blast: A New Disease in California." Task Force members include representatives of the Colusa and Glenn County Agricultural Commissioners, the California Cooperative Rice Research Foundation, Inc., the California Rice Industry Association, the University of California, Dept. of Plant Pathology, the University of California Cooperative Extension and the Rice Research Board.

To get a copy of the UC blast fact sheet or for further information on the rice blast disease please contact UC Farm Advisor Steven Scardaci, at the Colusa Co. UC Cooperative Extension office, (916) 458-0578.