These are organic fungicides commonly recommended for use on a variety of vegetables:

Bacillus subtilis is a naturally occurring bacterium helps suppress fungal diseases by colonizing plant surfaces and producing antibiotics that kill fungal pathogens. It can be used on a variety of vegetables, including tomatoes, peppers, beans, cucurbits, and onions.

Bordeaux mixture is a copper fungicide that can be used to treat a wide variety of fungal diseases, including early blight, late blight, septoria leaf spot, anthracnose, and bacterial spot-on tomatoes, potatoes, peppers, and cucurbits (including cucumbers, squash, and melons). However, copper fungicides should not be used on cucurbits within 14 days of harvest. They should be applied with caution as excessive use can lead to copper accumulation in the soil.

Neem oil is derived from the neem tree and is effective against a wide range of fungal diseases such as powdery mildew, rust, and black spot. It can be used on tomatoes, green beans, squashes, onions, potatoes, cucumbers, cantaloupes, and watermelons.

Sulfur is another organic fungicide effective against fungal diseases like powdery mildew and rust. It can be applied as a dust or spray and is safe for use on most vegetables, including the ones you listed.

Always be sure to follow the label directions carefully when using any fungicide, organic or synthetic. It is also important to note that organic fungicides are not always as effective as synthetic fungicides. If you are having a serious fungal disease problem, you may need to use a synthetic fungicide.