THE REDUCTION OF CHEMICAL CONTROL OF LEEK RUST, A SIMULATION STUDY

A model is presented which simulates chemical control against leek rus t under a system of supervised control. The spread of disease between fields in one farm and the influx of spores from outside is part of th e model. The possible reduction in fungicide sprays against leek rust following various preventive measures is estimated with this model. Re sults from this preliminary model suggest that supervised control of l eek rust will result only in a considerable reduction in the number of fungicide sprays if the leek fields are sufficiently isolated and the planting material is initially disease free. Where isolation between the fields is not feasible, overlap between successive crops should be avoided. Without the use of these preventive measures, there is littl e prospect for supervised control and the grower will have no option b ut the heavy use of fungicides.