Growing Magazine - April, 2014

COLUMNS

Orchard Management: Pruning Peach Trees for Maximum Production

By Sally Colby


Dr. Jim Schupp conducts a pruning demonstration. Removing any shoots that are shorter than a pair of thinning shears helps achieve a good balance between the photosynthetic potential of the leaves and the bearing surface of the plant. Cleaning up these shoots during pruning means less hand thinning and ensures fruit will have adequate leaf area to support growth.
Photos by Sally Colby.

The goal in pruning peach trees is the same as for any other fruit tree: to improve fruit size and quality. However, peach trees require a somewhat different pruning method than apple trees. In addition, this year's severe winter weather may have a direct influence on peaches this season.

"When you prune a fruit tree, no matter what species, you lower their resistance to cold and temperature extremes," said Dr. Jim Schupp, associate professor of pomology at Penn State University. "One thing about pruning after a winter like we had is the bud survival. From what I've seen, we have damage already."

Schupp said that in general, peach buds begin to die at minus 10 degrees Fahrenheit, and trees start to die at minus 15 degrees Fahrenheit. It's likely that the winter temperatures affected buds to a point where nature has taken care of some pruning, and this may reduce the need for thinning after pruning.

Peach trees grown in the open vase (or open V) system have several advantages, including short height for easier labor. Heavy pruning in a V system stimulates branch renewal. The perpendicular V system, in which the canopy is split into two narrow tree walls, lends itself to mechanized systems, as well as increased fruit yield and desirable color. However, tall trees create labor challenges, and renewal pruning in perpendicular V systems is not as successful as it is for apples.

"Whether it's a low, open-center tree or a V-type tree, there are permanent branches that are the scaffolds," explained Schupp. "Two-year-old or older wood is secondary wood, and the shoots that grew last year are fruiting laterals."

Schupp reviewed the three major pruning cuts: heading cuts, in which a portion of a branch is removed; thinning cuts that remove a branch at the point of origin; and renewal cuts, which take branches back to a shoot that will be retained.

"When we talk about renewal cuts in apples, we use stub cuts and remove a branch close to its point of origin, leaving a duck-billed stub," said Schupp. "That doesn't work well with peaches; that's why we have to make a different renewal cut on peaches."

When pruning trees in an open V system, identify each scaffold and make thinning cuts to remove strongly upright branches as well as pendant branches - those that are growing downward. Removing upright branches helps maintain the short height of the tree, and removing pendant branches is important because those branches tend to be weak and shaded and to bear small fruit. Schupp said that whether the tree is short or tall, the main objective is to remove the most upright branches.



Dr. Jim Schupp shows permanent branches, or scaffolds, which are the large limbs originating from the tree trunk. These limbs are the permanent supporting structure for bearing limbs.

Schupp explained that longer shoots will produce additional leafy shoots in summer. "Shoots that are less than about 6 to 8 inches long should be removed, because thin, short shoots will produce small fruit," he said. "It's more cost-effective to remove these shoots with pruning cuts than to have to come in later and thin fruit from the same shoots."

To obtain a good balance between the photosynthetic potential of the leaves and the bearing surface of the plant, anything that's shorter than a pair of hand shears should be removed. This also reduces the amount of hand thinning that will be necessary. Chances are there will be enough fruit on the tree without those small branches, and cleaning them up during pruning means less hand thinning and ensures that fruit will have enough leaf area to support growth to a good size.

The bench cut for the peach tree is essential to slow the upward growth of the canopy. Such cuts can contribute to lower production, which can be viewed as either positive or negative, depending on other thinning options employed by the grower. A properly made bench cut can stimulate vigorous regrowth in the canopy. While the cut can stimulate renewal shoots, it can also shade the lower canopy, resulting in lower production and quality. The bench cut can also increase the risk of canker.

"Although it isn't a desirable cut in apple pruning, the bench cut is necessary in peaches, especially in open-center systems," noted Schupp. "After thinning strongly upright and overly pendant branches, the next step is to bench back some branches." Schupp noted that although he doesn't like to make a bench cut into a strongly upright scaffold, he would rather make that cut and eliminate such a branch. "Where the branches angle and aren't vertical, that's where you make a bench cut."

Dr. Rich Marini, professor of horticulture at Penn State, said that only a certain number of peaches can be properly sized per acre, and that number will vary according to the variety. With a large variety like Loring, more fruit can remain on the tree than with a smaller variety like Redhaven. When pruning for specific crop goals, Marini likes to aim for three or four fruits on a shoot.

"You have to figure out how much fruit per acre you want, [then] divide by four, and you get the number of shoots you want per acre," said Marini. "Then divide by the number of trees, and that will tell you how many shoots per tree to strive for." Marini said that he prunes first, then counts shoots on several pruned trees and takes note of what the tree looks like. "I don't count every tree," he said. "Once you know what the tree should look like, you can prune the rest of them the same."

The author is a frequent contributor and freelance writer who farms and raises Great Pyrenees in south-central Pennsylvania. Comment or question? Visit http://www.farmingforumsite.com and join in the discussions.