Have you been getting cucumbers from your plants? Hopefully, a good few, now! if so, your plants may simply be exhausted, and at the end of their fruitful lives. If not, and they are turning yellow and papery, your watering regime has not been regular, or you have not been feeding them with a potash-based liquid feed, same as ones for tomatoes, courgettes, etc. This is not generally done before signs of the first fruits, however.