If you are uncertain about diagnosing blast symptoms, send a sample to your local University of Missouri Extension center for identification. Symptoms present early in the season should warn you that the disease may occur in midseason. You should continue to scout for blast near the heading stage and watch carefully for flagleaf collar symptoms on early-planted susceptible varieties. Also, devote time to determine the stage of rice development to see if the DD50 predicted time frame for fungicide treatment for blast is correct. Symptoms appear 4 to 6 days after infection, so rice heads may be infected without symptoms appearing.
Preliminary research indicates other inoculum sources exist including seed.
The fungus has been isolated at low levels from seed. Seed may carry blast spores that could cause early seedling infection and symptoms. Seed treatment in general is good insurance against seedling diseases and is likely to stop any seed transmission of blast. It will not prevent infection from wind-borne spores. Not all seed treatment fungicides are effective.