Research has refined pruning concepts
Not available – first paragraph follows: In the wild, the grapevine is often supported at great heights by adjacent trees; the shoots cling to branches by means of tendrils and trail for considerable lengths. A favorable light environment is essential for annual growth, so lower or interior areas are characterized by rope-like “trunks,” devoid of leaves, extending from the ground upward to the canopies of trees. Not only is the fruit difficult to locate and harvest, it consists of a myriad of small straggly clusters. Productivity is erratic from year to year.