The Importance Of Dormant Pruning

Dormant pruning is important for ensuring balanced crop load in the Lake Erie Grape Belt.

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Terry Bates, director of the Cornell Lake Erie Research and Extension Lab in the College of Agriculture and Life Sciences, says healthy Concord vines at standard spacing (9 feet between rows and 8 feet between vines) will grow 500 to 600 cold-hardy fruiting buds.

“If left alone (unpruned), the 500 fruiting buds would produce far too much crop that could get ripe by the roots and shoots working in the 72 square feet,” Bates says. “Over-cropping reduces vine leaf and root growth, decreases future crop potential and decreases the rate of fruit maturation – all bad from a viticulture standpoint.”

Concord vines can be pruned as soon as the leaves are off the vines. But figuring out exactly how much to prune can be tricky. The goal, Bates says, is to balance the vine leaf area to the fresh fruit weight to maintain vine vegetative growth as well as quality fruit development.  However, a number of factors influence crop potential, including vine health or size, fruiting bud differentiation in year one, cold temperatures in the winter, spring bud development in year two, spring frost potential, bloom and fruit set, and fresh berry weight development.

“Many of these factors can be difficult to measure or predict, so it makes the pruning level decision difficult,” Bates says.

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Deciding How Much To Prune
Adjusting the pruning level based on the vegetative growth of the vine is one method of achieving balanced pruning. “A big vine with a lot of dormant wood can potentially carry and ripen more crop, so growers will leave more buds,” Bates explains. “Small or sick vines with less ripe wood need to carry less crop to recover, so growers will leave fewer buds after pruning to reduce crop level.”

He adds that balanced pruning is generally conservative. “It reduces the crop so that all the fruit gets ripe in the poorest growing seasons,” he says. “The negative side is that in good growing seasons, the vines could ripen more crop than was left during dormant pruning, and the grower can’t glue on more crop after it has been pruned off.”

Growers who prefer to err on the side of caution will sometimes leave too many buds on purpose so they can instead balance the crop load later in the spring. “If the crop develops and sets normally and there is a very high crop level and potential over-cropping, Concord growers can reduce the crop size through mechanical shoot thinning or mechanical fruit thinning,” Bates says.

Maintaining Vine Health During Winter
Balanced vines have the best chance of surviving extremely cold winter temperatures. However, even with optimum crop load balance, vines can still be susceptible to winter injury. Bates says that last year’s Concord buds were hardy to -22 degrees F. Temperatures in the region dropped as low as -19 F in some areas to -29 F in others. “Therefore, some vineyards received no damage while other vineyards received 100% primary shoot loss with crop only coming from secondary shoots,” he says.

But balance is still a grower’s best defense. “Vines that are balanced will fully ripen fruiting wood going into the dormant season, and they will have maximum cold hardiness,” Bates says.

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