The timing of benomyl applications at the full boot and head exsertion growth stages was derived from years of fungicide research. Yield responses were the greatest when benomyl was applied at those two stages rather than others. A surfactant may enhance fungicidal control of blast as shown in some Arkansas tests. The additions of a surfactant may be useful if cost is not excessive. Scouting Leaf symptoms will appear most readily on plants at the edges of fields, on levees, in areas of the fields that are shaded in the morning, or in areas that received excessive nitrogen.
Symptoms are usually worse on drought-stressed rice.
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.