Bill we were growing stonefruit in a high humidity situation not far from the coast. At the time we were growing very conventionally and having a lot of trouble with brown rot.

We converted to a biological growing system, and increased things such as calcium, and the impact was immediate. All fungal disease just disappeared. I learnt later that I was raising the sap pH with my actions and that will have had a major bearing on disease susceptibility.

As for using horticultural oil for disease control I have not used it directly. However many years ago we had a researcher who had spent many years working with oil, tell us we should be considering oil for disease control because it definitely worked.