Neem oil has fungicidal characteristics. By that we mean that it will prevent a fungal disease from appearing if it has been sprayed on the plant before the disease develops. If a fungal disease has already reared its ugly symptoms, then the neem, or any other fungicide for that matter, cannot repair the damaged part of the plant. What it does, if immediately applied, will be to prevent the further spread of that fungal disease.

Just as you used neem to repel certain pest insects, you try to anticipate when a certain fungal disease appears on a certain plant, and then apply the neem a few weeks before. Usually fungal diseases, like pest insects, are active for a limited period of time, seldom more than a month to six weeks.

For more information see the file Using Neem Oil

If this product comes in a concentrate form you will need a sprayer. Go to Hand Tools For Spraying in Yardener's Tool Shed.