i don't worry too much about one plant infecting another if there's some space in between them.
sometimes it can be something like a mutation which some plants have happen which will do them in. other times it can be a disease or attacks by bugs, other times it is the hot weather... etc. that is why planting diversity and in numbers is a good thing as it gives chances for some plants to fail and others to do ok and give results.
be glad you don't have deer, rabbits and groundhogs...
if you are spraying with soapy water it is a chance that might be the problem. not sure it will recover. don't sweat it. other three might produce enough.
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