For use of coppers, see the alphabetical entry Copper Fungicides. Mefenoxam or metalaxyl as applied for root rot should suppress downy mildew.
Resistance is likely to develop.
Protective sprays with fungicides that contain mancozeb or chlorothalonil as recommended for other problems should be used. Downy mildew can be devastating to seedlings. Alternate between trifloxystrobin and non strobilurn fungicide to avoid resistance development. Do not use with organosilicate additives to the spray tank.