Applied either directly on the leaf or into the soil. Calcium reduces certain types of bad bacteria, fungi found in many diseases. Also beneficial bacteria enjoy the calcium in their diet. So a good spray will naturally be a mixture of calcium and a bacterial source. Calcium can be obtained from crushed egg shells.
Bone meal is also a good source of calcium.
Copper Copper is an excellent natural fungicide, controls diseases of vine crops, potatoes, leaf spot, anthracnose, downy mildew, powdery mildew, scab, fire blight, bacterial spot. Available in liquid or dust form. Excellent for use on melons and cucumbers. Can be used as a liquid for spraying or as a dust for dusting. Magnesium Is available in Epsom salts.