We grew 2 varieties of cukes last summer and had a huge harvest. This year we had many volunteers come up. I put up trellises and let them grow. They have spade-shaped leaves and vigorous vines and are now producing white flowers- but no sign of any fruit. Is it possible that an infertile hybrid was created?
It's possible, but your problem may actually be a lack of pollinators for your blooms. You can do that yourself with a small paint brush. For successful veggie growth, do try to include some plants in and around your garden that draw bees, hummers and other pollinators.