Downy mildew factsheet with pictures: https://www.vegetables.cornell.edu/crops/cucurbits/downy-mildew/

Some helpful info for organic fungicides for DM:

https://www.vegetables.cornell.edu/pest-management/disease-factsheets/downy-mildew-of-cucurbits/list-of-biopesticides-for-organic-production/

Info on managing DM:

https://www.vegetables.cornell.edu/pest-management/disease-factsheets/downy-mildew-of-cucurbits/current-management-guidelines-based-on-research-results/#4