Simulation modelling of the spread of rice tungro virus disease: the potential for management by roguing.
A simulation model of the dynamics of rice tungro virus disease (RTVD) [rice tungro spherical waikavirus and rice tungro bacilliform badnavirus] was developed to assess the potential of disease management options in different cropping systems. The model simulated the position and infectivity status of the green leafhopper (Nephotettix virescens) vectors and the corresponding RTVD infection pattern in a square grid of 324 rice hills, during the first 60 days of crop growth after transplanting. Based on published information, assumptions were made regarding rates of virus transmission, vector population dynamics and probability of vector dispersal. Results from a programme of field experiments in the Philippines provided a basis for model testing. Simulation analysis was used to examine the feasibility of roguing (replacing those plants which show symptoms with healthy plants) as a means of preventing further disease spread. A genetic algorithm was used to evaluate the sensitivity of model output to parameter changes. Particular parameter combinations were found to be associated with effective roguing. In general, with high or moderate disease pressure, simulated roguing was relatively ineffective even when done frequently and efficiently. With low disease pressure, roguing had a significant effect, but was of little value in such circumstances.