Most mildew infestations of cucumber plants are carried in by the wind. Two natural organic solutions to a mildew problem are a milk solution and a tea made from chives. However, for some more resistant infestations, a harsher natural or chemical fungicide may be required. If you live in an area prone to mildew, you can use either the milk solution or the chive tea as a preventative measure.
Mix one part milk with one part water. An enzyme in the milk helps control cucumber mildew.
Spray the plants every three or four days when you first notice the mildew.
Spray the plants weekly as a preventative measure for mildew and several other fungal diseases.
Put a cup or two of chives in a glass container.
Cover the chives with boiling water.
Strain the mixture.
Spray your cucumbers two or three times a week as a preventative measure.
Other Natural Fungicides
Apply a natural copper-based fungicide according to label instructions. Be careful, however, as fungicidal levels of copper can be toxic to some beneficial organisms, like earth worms.
Apply a fungicide containing neem oil. Again, although it is a natural fungicide, the concentrations may be toxic to some organisms, like ladybugs.
If all else fails, try using minimal quantities of chemical fungicides. Be aware, though, that these can harm beneficial organisms and are not considered organic.