You will need to regularly prune the dragonfruit cactus plant growing on the dragon fruit trellis or else it will grow into a dense heavily branched mass which will block light, encourage fungus and bacterial disease, and make fruit harvesting hard to carry out.
Prune the growing dragon fruit cactus vine structure to remove always any diseased and dead branches of the mature dragonfruit cactus, and to not let branches droop all the way to the ground where they can pick up rot. As the dragon fruit cactus plant is a quickly growing fruit plant, regular pruning may be required more than once per year if the dragonfruit cactus is growing vigorously. After pruning, the cut ends of the pruned dragonfruit cactus may be treated with fungicide to help prevent rot at the pruning cut. For the same reason, compost the dragonfruit prunings away from the dragonfruit plants themselves to avoid the spread of rot. If your prunings are from high quality and productive plants, you may also want to use some of the prunings as dragonfruit cuttings to start new dragonfruit cactus plants.
You will find that pruning also helps to promote blooming and stem branching and will increase your yield of dragonfruit fruit commensurately.