Muscadine grapes, also known as Scuppernong grapes or Southern Fox grapes, tend to grow wild in the southeastern parts of the United States. This grape is very high in antioxidants and, according to the USDA, "concentrations of these compounds (phenolic) present in the muscadine grape equal or exceed that known for other small fruit." Pruning muscadine grapes into submission produces better grapes and a healthier vine.
Identify the main stem of the plant. Muscadine grapes can grow voraciously, even up to 50 feet in one season, so you may find that you have a very long, thin vine as the main branch. Trim this back to about 5 feet from its roots. Tie it to a trellis if possible to keep it upright and exposed to sunlight.
Trim off any side shoots growing from the 5-foot section you have left, so that they are only about 6 inches long. If the stem is covered in side shoots (not likely for very long vines), trim them back almost flush with the main stem and leave just three or four 6-inch sections. These will develop into your laterals. Typically, gardeners line up the 6-inch laterals with the wires or supports on a trellis.
Allow the muscadine grape vine to grow during the summer. You may have some fruit growing on the wood that you did not prune off. If it is an older vine, let the fruit grow. But younger vines benefit from pruning the fruit off to push the plant's energy into the vine. Keep the growing vines tied to a trellis to keep them in shape, and don't allow the laterals to grow more than 5 feet long.
Clip off any dead or diseased wood that you see during the growing season. If the top of the vine buds out and tries to grow, keep it pruned so that it stays at the 5-foot height. This will force the plant to grow laterally. Make all cuts at a 45-degree angle and just 1/4 inch after a bud.