Extension Communications Extension 4-H Youth Building Ames, Iowa 50011-3630 (515) 294-9915

4/5/04

Contacts:
Dennis Portz, Plant Health and Protection and Horticulture, dportz@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Yard and Garden Column for the Week Beginning April 9, 2004

Pruning Apple Trees

By Dennis Portz
Horticulture and Plant Health and Protection Student
Iowa State University

Apple trees are a popular choice for home landscapes and are valued for their attractive spring blooms, their cooling summer shade and their delicious fruit. By maintaining a healthy apple tree, you can enjoy its benefits for many years. Pruning the tree each spring is one important aspect of keeping a tree healthy and productive.

Before you begin pruning, ask yourself "Why am I pruning this tree?"

The answer is annual pruning of your apple tree will help produce good quality fruit as a result of greater light penetration and air circulation inside the canopy of the tree. In addition, proper pruning will result in the development of a strong branch framework that increases the tree's life, simplifies harvest and creates an attractive feature in your home landscape. By neglecting pruning, your tree could grow misshapen and yield poorly.

Pruning is best done in late February to early April, while the trees are still dormant. The leafless canopy allows you to easily see and remove any undesirable, diseased and broken branches. Also, callus readily forms over pruning wounds during the spring growing season.

The system used and the amount of pruning needed varies with cultivar, age, existing framework, vigor and health of the tree. For example, an apple cultivar such as "Gala" grows vigorously and may require more annual pruning than a cultivar such as "Red Delicious," which does not have as vigorous of growth. Pruning of very young trees will encourage growth of lateral shoots and give the tree better architecture. However, excessive pruning of older, established trees may result in excessive growth and a poor fruit crop the following year. Broken or diseased branches should also be removed.

Two basic cuts are used in pruning apple trees; heading-back and thinning-out cuts. A heading-back cut is the removal of a portion of a shoot or branch and typically is made on one-year-old lateral shoots or the central leader of the tree to encourage new scaffold branches that will form the basic framework of the tree. A thinning-out cut is used to completely remove unwanted shoots on scaffold branches, such as upright shoots, commonly know as water sprouts, which normally don't produce fruit. Lateral growths from scaffolds are desirable, but thinning-out cuts may be needed on lateral branches of mature trees to avoid shading of fruiting spurs.

Fruiting spurs are short branches that produce flowers and fruit. When pruning, be careful not to break fruiting spurs or to accidentally remove them. A heavy fruit crop in one season often results in a poor crop the following year because large fruit crops deplete the tree's food reserves for next year's flower bud formation. So remove excess fruit (fruit thinning) to help apple trees produce a good crop of fruit each year. For the home gardener, removing excess fruit by hand is the best way to thin the crop. Thinning should be completed by early June.

An apple tree produces vertical branches that grow parallel to the central leader. However, only one leader commonly is desired. These upright, vertical branches tend to grow vigorously and compete with the leader. Therefore, clothespins, spreaders and weights can be placed on the other vertical branches to increase the angle of the crotch of these branches with the leader, thus reducing competition for light and increasing air circulation throughout the canopy.

Increased air circulation promotes drying of plant surfaces, which can reduce infection by certain diseases, such as scab, cedar-apple rust and fire blight. These diseases not only damage leaves and fruit, but also may reduce tree vigor.

Pruning is especially important in preventing the development of fire blight. It is also a primary control strategy to be used when the disease does occur. A classic symptom of fire blight is blackened, shepherd's-crook-shaped branch tips. To control the disease, prune diseased branches 6 to 12 inches below the edge of the visible symptoms. If the infection has spread to the trunk, the tree should be removed. Pruning fire blight out of your tree may seem like a drastic measure, but is necessary to prevent further spread of the disease throughout the tree or to neighboring trees.

Additional information on pruning can be found in ISU Extension publication "Pruning and Training Fruit Trees" (PM 780.) A list of suggested apple cultivars for Iowa can be found in ISU Extension publication "Fruit Cultivars for Iowa" (PM 453.) Both publications can be ordered through your local ISU Extension county office.

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Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The fullsize photo is 576K. Caption: pruning

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