Common types of plant diseases are caused by:
a. Bacteria
b. Virus
c. Fungi
d. Insects
e. Nematodes
f. Phytoplasma
They cause blights, grey/white mold, powdery mildew, discoloration, plant stunning, bacterial or fungal leaf spots, fruit, leaf or root rot, wilting, etc as well as death of plant.
They enter through natural openings, wounds or come through environment, insects carriers or through human caused damage. Inspect your plants regularly and treat them before they r widespread.
Natural solutions for most of these diseases r spraying soapy water all over the plant and soil (to trap and suffocate the pests), homemade ginger garlic green chillies (GGG) solution, sprinkle haldi pd or solution, neem oil+soap solution (to help neem oil dissolve), gomutra solution, jeevamrut solution, bio-enzyme solution, fermented buttermilk solution, fermented cooked rice solution, tobacco solution, etc…all in proportion of 10 ml to 1 litre. They need to be sprayed regularly initially to remove the disease/pests in frequency of a week and later as preventive measure every fortnight. Apply/spray various natural pesticides in rotation to keep the odour on the plants to repel the pests.