First my apologies for taking so long to answer this - just now found this. Next my sympathies because it looks like your plants have the dreaded cucumber wilt disease and there is no cure. Pull up the plants if you have not done so already. This is a bacterial disease spread by the striped cucumber beetle. There is no cure. IN the future cover newly planted cucumbers with floating row covers or cheese cloth to keep the beetles from landing on the leaves and infecting them with the bacteria. There is also a more wilt resistant cucumber variety called Liberty that you may want to try. Don't give up, and at least you know the problem had nothing to do with the heat from the white fence. Keep growing, Marianne Binetti