Cucumber – Downy Mildew
Q: I believe I have cucumber mosaic virus in my garden. It has spread throughout – on squash, zucchini, and cucumber. Is it likely that is was caused by all the summer rain? Is it o.k. to eat the fruit from infected plants? The foliage looks terrible, but the fruit looks normal.
A: I don’t think it’s cucumber mosaic virus (CMV). The curcubit fruit should look weird: warty and mottled. Also, the virus usually stunts the cucumber vines and yours looks normal sized.
My diagnosis? Downy mildew on your squash, cucumber and zucchini.
Here are the symptoms: Pale green areas that change to yellow angular spots bounded by leaf veins The spot is brighter yellow on the upper leaf surface than on the lower leaf surface. Usually older leaves are affected first, then younger leaves. Fruit are usually not affected When the weather is moist, the undersides of the spots will be covered with a gray-white layer of fungus.
Downy mildew likes high temperatures and high humidity, of which we have had lots.
Mildew can be controlled with fungicides. The fruit is fine to eat if it looks normal.