The Concord grape and grapes of this type and hardiness, which are the grapes most widely grown in Iowa, require yearly pruning if the grower wishes to obtain heavy annual yields of large-sized high-quality fruit. The illustration on the cover of this bulletin indicates the development and distribution of the fruit which may be expected on correctly pruned vines.
Far too many home vineyards are left unpruned or are incorrectly pruned with the result that they are unproductive and unsightly. There are many systems used in training the American grape, but the system which seems to be best adapted to Iowa conditions is the single-stem four-cane Kniffin system. The spur method of pruning, which has been employed to a considerable extent with the European grape, is still followed in many sections of Iowa. Unfortunately, this method is unsatisfactory with the Concord grape and, except with grapes trained on arbors, should not be used. The grapevines pruned by the long cane method and trained to the Kniffin system in certain Iowa tests have repeatedly out-produced those pruned by the spur method. The Concord produces the heaviest yield of fruit from approximately the fifth to ninth bud and the lowest yield from the first four buds on the cane. Therefore, it can be seen that with the spur method of pruning, when only the first two buds are left on each cane, the heaviest producing buds are removed. The characteristic bearing habit of the American grape explains why long cane pruning is more productive than the spur cane system.
Edgecombe, S. W. and Maney, T. J.
"Grape training and pruning in Iowa,"
Bulletin P: Vol. 1
, Article 1.
Available at: http://lib.dr.iastate.edu/bulletinp/vol1/iss7/1