Neem is turning heads everywhere. It is an insecticide and a miticide and a fungicide all wrapped up into one package. It is extracted from the seed of the neem plant. The oil portion acts like any ultralight horticultural oil in that it smothers some hard to control sucking insects that attach themselves to plants permanently bu clogging their breathing apparatus. Neem Oil also contains an active ingredient, azidiractin which has insecticidal, miticidal and fungicidal properties.
Neem oil is effective for a variety of mites, aphids, powdery mildew, black spot and botrytis.
Probably a few other fungal diseases too. Like any pesticide, the azidiractin is no less a poison, even if it is botanical. It should be treated as such. There is also the issue of resistance developement as there is most any pesticide. If it is used too often in succession pests will begin to develope resistence to the poison.