The first and most crucial step to take is understand how to prevent disease in the first place, for prevention is always better that having to cure and get rid of disease or parasites.
So before you are faced with these problems do all you can to prevent disaster and follow the following steps.
When gardening take advantage of materials that you can use for natural composting. Be careful for not all elements have the same period of degradation as others. You may need to wait more for others to have a good an healthy compost for your garden. If you do not wait sufficient, you may risk introducing infected debris, for composting generates high temperatures that kill any pathogens that may infect your plants.
So although compost is excellent for your garden if you are not sure whether your compost pile is ready avoid using it.
Always keep an eye out for any insects or pests that may be present on your plants. Some insects can carry viruses and pass them on to the plant, which can in turn pass it to the others plants. So treat your plants immediately in order to keep up their strength.
Keep your garden free from debris and leaves especially in autumn. Keep it clean as this will deter any disease and control the bacteria and viruses in your garden. Always make sure you apply the right type of fertilizer, for too much product may weaken plants and expose them to viruses.
With these few tips you can keep your garden in excellent health and take advantage of its beauty in all seasons.