Apr 30, 2009
Summer Pruning, Done Right, Is Quite Effective on Apples

There are many elements, pros and cons that go into the decision to summer prune apples. There are some rules for applying this practice to make it a positive experience, because otherwise the grower may see some negative results.

Considerable research has been conducted over the years and there are some excellent references that help shed light on the subject. One is a 166-page paperback book, “Training and Pruning Apple and Pear Trees,” authored by C. Forshey, D. Elfving and R. Stebbins, published in 1992 by the American Society for Hort Science.

In this article, I will discuss some of the primary issues related to summer pruning. Remember that summer pruning alone is not a practice that will deliver positive results. It can be very effective when used with good timing to supplement dormant pruning.

Summer pruning is very effective in controlling growth and removing unwanted growth on young, developing trees. Pinching off strong, competitive laterals in the upper region of central leader, vertical axe or slender spindle trees will maintain a strong growing leader. Realize that if done too early (before laterals have 6 inches of growth) re-growth is possible, so wait until mid-July to avoid requiring a second pinching. In all cases, whether in a young or mature orchard, wait until prime fire blight conditions are past before attempting. I have actually spread fire blight among young trees by not waiting until the weather was dry and hot.

When summer pruning mature trees, removing growth to open canopies to allow more light and improve fruit color is effective. It is possible, however, to not see an improvement in fruit color with pruning under warm, humid fruit development conditions. There is some potential for sunburn, but in our climate in the eastern United States it is less of a problem than in the West.

Remember that it needs to be accomplished prior to four weeks before harvest. This should be done in late July in Michigan. Pruning for this purpose can be a trade-off, as a grower will see a reduction in fruit size, especially if pruning is done late (approaching harvest). It is also possible to see a reduction in yield and soluble solids.

Any summer pruning should be accomplished after the apical bud sets. If shoots are removed before terminal bud set, expect to see re-growth near cuts. Excessive early pruning can also reduce conversion of shoots into spurs and delay or inhibit flower bud initiation.

Watersprouts can be removed anytime, especially in the early part of summer. Watersprouts have a tendency to shade canopy interiors and draw calcium away from fruit, aggravating bitter pit problems.

Summer pruning cannot make up for excessive crowding associated with vigorous conditions or selection of vigorous rootstocks for the spacing.

Summer pruning can be very effective when managing high-density plantings, if done at the right time. One of the benefits of summer pruning is less compensatory growth in response to cuts, as long as it is performed in a moderate way (avoid excessive summer pruning).

It is possible to summer prune after the terminal bud has set to inhibit lateral shoot extension and impending encroachment on neighboring trees or alleyways. This can be done by making a thinning cut back to a weak lateral or fruit spur.

This is also the best time to prune if trees are getting too tall. Although you may remove some fruit, making a thinning cut in mid- to late summer back to a lateral-bearing fruit can lower canopy height and avoid shading on neighboring tree rows. Lowering tree canopy during summer lessens the chance for compensatory top growth compared to performing this operation in winter.

In visiting a tall spindle orchard in western New York last summer, I saw how one grower had developed a sicklebar hedger to “summer-sheer” the sides of his canopy to maintain a narrow canopy and reduce the amount of pruning time/labor during winter. The practice appeared economically feasible and effective in his operation. Careful follow-up hand pruning in the winter is needed any time mechanical devices are deployed and cuts are made in arbitrary planes of dimension.

Many growers who have super-slender spindle plantings do the bulk of branch removal during the summer, to remove unwanted strong growth and avoid the compensatory strong growth response commonly experienced after winter pruning.

Summer pruning can be a very effective tool in the right hands and deployed at the right time. Be aware of pitfalls that go along with the benefits.




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