The Gompertz model was superior for describing increase in disease incidence and disease severity in all three citrus nurseries. The rate of disease increase was greater in the most susceptible host, Duncan grapefruit, than in less susceptible hosts, Pineapple orange or Swingle. Disease spread coincided with rain splash dispersal and a rapid increase in the apparent infection rate after windblown rainstorms. Rate of disease spread was independent of wind direction. Aggregation of diseased plants was observed in all three nurseries throughout the duration of the tests. Secondary foci were established early in the epidemics and soon overcame the effect of the original focus of disease
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T. R. Gottwald (1989) studied this question.