High humidity and warm temperatures are the best recipe for sheath blight (Figure 1) disease to progress fast (Figure 2) in rice. The disease progresses fast both vertically and horizontally. After this rain, scout more frequently and act immediately if the disease is at threshold. To read more on how to scout and the thresholds, review my post on scouting.
To minimize grain yield loss due to sheath blight, protecting the upper three leaves including the flag leaf is very important. Once sheath blight gets to the flag leaf it can easily get to the panicles (Figure 3). Moreover, sheath blight weakens the stem and in severe infestations, rice can easily lodge.
Note: Correct diagnosis of sheath blight is important to avoid unnecessary fungicide applications since symptoms of other rice diseases such as aggregate and bordered sheath spots, black sheath spot and stem rot symptoms may be confused with those of sheath blight. Table 1 below shows the recommended fungicides for managing sheath blight in Arkansas rice.