If plants are healthy when this disease hits, they will likely produce a modest crop. Plants that have lost more than one third of their leaves to downy mildew are not likely to produce well.
Choose resistant varieties, which are widely available. Make sure plants get good air circulation and plenty of sun, and keep weeds controlled to promote prompt drying. Rotate cucumber family crops to a fresh site to prevent disease buildup, and use mulch to keep soil from splashing onto plants during heavy rains. Avoid using sprinklers or other overhead irrigation methods if conditions are cool enough for downy mildew.
Clip off and compost affected leaves, and then spray plants with 1 teaspoon baking soda mixed with one litre of water. Cucurbit downy mildew usually disappears if the weather becomes warm and dry.