My armenian cucumber has really taken off and is now over flowing beyond the bamboo trellis. Is it OK to prune? Same with some volunteer pumpkin and melons. Will pruning kill the vine or make it diseased?

Over the last week, there seems to be a lot of powdery mildew as well. Wondering if I should spray with something. Some advice on the web suggests a milk spray or a neem+baking soda spray with few drops of dish soap.