he best way to prevent downy mildew is to avoid the environmental conditions that favor the disease.
Prune or stake plants and remove any weeds to improve air circulation.
Water in the early morning hours, or use a soaker hose, to give the plants time to dry out during the day.
Keep the ground under infected plants clean during the fall and winter to prevent the disease from spreading.
Remove and destroy any plants with serious infection (see Fall Garden Cleanup).
Choose resistant varieties whenever possible.
Downy mildew is comparatively easy to control on most plants when the foliage and fruit are kept protected by organic fungicides. If you catch the infection early, apply a copper spray to diseased and surrounding plants every 7-10 days until harvest.