A systems model was developed to simulate rice sheath blight (ShB) epidemics over lime. The model considers the two phases of ShB epidemics: mobilization of soil-borne primary inoculum and secondary spread. The mechanism involved in secondary spread is a key feature of ShB epidemiology. Once infected, a tiller may in turn infect its neighbors via direct contact between leaves, which enable mycelial strands of the fungus to spread in the canopy. While the primary phase of epidemics is dependent on soilbome inoculum, the secondary phase involves leafborne inoculum and depends on crowding of canopy and climatic factors such as leaf wetness, tight, and relative humidity for its multiplication.
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