He is not ready just yet. That is called a keiki. To remove it, simply grasp it close to the 'mother' plant and give it a little twist. If the dendrobium cane is an older cane that I would normally remove when repotting, I also like to take a sterile knife or blade and cut about an inch above the keiki and an inch below the keiki and leave the keiki attached to the old cane. The cane is then buried in the bark when potting up the keiki and helps support the new plant. Eventually, it will rot away. (Oh, and remember to take pruning seal to the ends of the cane to keep infection and other stuff out!)
Cheers,
BD