Water early or use soaker hoses.
“Water in the morning” This is one of those old tried-and-true bits of advice that many think is just an old wives’ tale, but really, it makes sense. Many fungal diseases need damp, cool environments to thrive. So if our plants’ foliage is wet overnight, that gives these diseases very favorable environment in our garden. The easiest way to prevent this is to water as early in the day as possible, so that your plants can dry off before nightfall. Bottom watering with soaker hoses eliminates this issue. Yes rain will get on the leaves, but adding our own water to the plants and leaves only perpetuates the problem.
Watch out for insect pests, they can harbor and introduce diseases to your plants.
Insect pests, with their chewing and burrowing, are a problem in and of themselves, with the damage they can do to your plants. But, many of them, such as aphids, are a double-threat because they transmit diseases between plants. Stay vigilant, and try to eliminate insect pests as soon as you see them. This is a frequently overlooked and highly underestimated form of disease transmission, and is very interesting to research. Many plant diseases actually are perpetuated by the bugs, as they become a host and the pathogens that would have died over winter survive in the bodies of the insects. Also, frequently seen, insects make possible the existence of a plant disease by obtaining, carrying, and delivering into host plants pathogens that without the work of the insect, would have been unable to spread, and thereby unable to cause disease.
Remove diseased stems and foliage A.S.A.P.
This is a simple organic start to disease control and often times, if caught, soon enough will prevent the spread throughout the rest of the plant, and you will still have at least some bounty in reward for your efforts.