In my experience, pruning cucumber vines can be beneficial for a few reasons. First, removing some of the leaves can increase air circulation, which can help prevent mildew and other fungal diseases. Additionally, trimming back the vines can encourage the plant to put more energy into producing fruit, rather than growing more foliage.
When pruning cucumber vines, it's important to be careful not to remove too many leaves, as the plant still needs them to produce energy through photosynthesis. It's also best to wait until the plant has developed a few true leaves before pruning, to ensure it has enough foliage to produce energy.
In terms of timing, I usually start pruning my cucumber vines once they reach the top of the trellis or other support. From there, I'll remove a few of the larger leaves at the bottom of the plant, as well as any smaller shoots that are starting to grow off the main vine. I'll continue to prune as needed throughout the growing season, depending on how the plant is growing and if I notice any signs of disease or pest issues.
Overall, I've found that pruning cucumber vines can be a helpful technique for improving plant health and encouraging fruit production, but it's important to do so carefully and judiciously.
