Spatially explicit simulation of aster yellows epidemics and control on lettuce

Aster yellows is a sporadic disease of vegetable crops (lettuce, carrot and celery) in the North Central US. The pathogen, a phytoplasma, is transmitted by the aster leafhopper (Macrosteles quadrilineatus Forbes). A simulation model has been developed to study the effects of spatial patterns of fields of host and non-host crops and spatiotemporal pattern of cultural and chemical controls for the disease and insect vector, respectively, on disease epidemics. The model is spatially explicit, simulating leafhopper reproduction, development and movement among individual fields. Simulations demonstrated that both the pattern of long range dispersal and the arrangement of host and nonhost fields can affect aster yellows epidemics and yield loss. If the source of inoculum is within the production area, insecticidal control of vectors in early plantings can protect later plantings, although protection may be more easily achieved by placing later plantings at a suitable distance from earlier plantings. Sensitivity analysis of model parameters also indicates that an increased crop incubation period, the time between infection and symptom expression, could greatly reduce losses from this disease in lettuce.