Use Compost tea. Some Diseases are introduced by Weeds. Use disease free seedlings and plants. Be especially careful when bring potted plants with soil into the home. Certain weeds are hosts to pests which carry the disease from one plant to another., therefore weed control of some type is important.
Weeds can also provide homes for many beneficial so choose carefully.
Some Diseases are spread by Insects. Many diseases are carried around by insects such as the ant. Control the insect populations in your areas. Learn what insects spread what disease. Improper Varieties Planted.