How To Avoid Pitfalls In Peach Tree Training
One of the major challenges of growing peaches is keeping the trees healthy. My main focus in this column is on the basic elements of good tree structure. By practicing proper tree training techniques chances for good tree longevity and productivity is improved.
Tree decline is most noticeable when the tree heartwood is invaded by wood-rotting fungi. In a healthy tree, the vulnerable heartwood is protected by the outer younger, metabolically active xylem layer, the sapwood.
Poor tree structure often leads to a failure of the sapwood layer to protect the heartwood, followed by general tree decline. The beginning of the decline can often be traced back to decisions made about training in the very first years of the orchard.
Distribute Scaffold Limbs
Trees with well-spaced scaffolds with good crotch angles are less prone to breakage by fruit loads and trunk damage by mid-winter low temperatures. A good rule of thumb is the trunk attachment points for scaffolds should be at least 12 inches apart to avoid future structural weakness and “plumbing” problems (Photo 1).
Scaffolds should be selected such that one is not “stacked” over another. The tree trainer should avoid the temptation to select all scaffolds in the first year of training. With peaches, it is generally easy to develop an additional better quality scaffold from a well-positioned side limb of an existing scaffold.
A common variation of the open center tree has three scaffolds that originate at about the same level and are spaced equally around trunk top (Photo 2). Although this method seems contrary to the 12 inch rule, it works because each scaffold has a good connection with the trunk and has wide crotch angles that are usually trouble-free.
Solve The Problem Of Co-dominant Limbs
A common problem to avoid in peach trees is upright parallel trunks or limbs (Photo 3). Bark inclusions in the narrow crotch angle of these equally dominant (co-dominant) trunks inhibit the development of strong structural wood. This poorly developed crotch area will tend to break under crop loads (Photo 4), windy conditions, and snow and ice loading situations. The problem of co-dominant limbs can be easily prevented by twisting off or hand pruning one of competing limbs when they are still tender shoots.
Peaches and many other woody species have a specialized structure called a branch collar which helps the tree to heal after a limb is removed. The branch collar is where the trunk and limb tissue merge in a puckered ridge (Photo 5). If all goes well, callus tissue generated from this tissue area grows over the pruning wound, eventually sealing the trunk from diseases and pests. Branch collars are generally found on side limbs that are less than half the diameter of the parent limb.
Co-dominant limbs typically do not have branch collars, which make these areas slow to heal if one limb is removed by pruning. Corrective pruning of co-dominant limbs is best done when the limbs are young and healing is more rapid.
A useful technique is to partially break one side within a few inches of the crotch and leave the broken limb in place. The intact limb becomes dominant over the injured side which can be removed by pruning in a month or two. This method has the advantage of correcting a co-dominant limbs problem without stimulating appreciable regrowth or increasing canker problems.
Avoiding Problem Areas On Ends Of Developing Scaffolds
Young peach trees that start and stop growing under conditions with varying water and/or nitrogen availability have the tendency to develop clusters of strong limbs at the end of developing scaffolds (Photo 6). These so-called “crow’s feet” clusters of branches have poor crotch angles and are difficult to prune without leaving wounds that are slow to heal. The typical strategy is to remove limb clusters by heading terminal branch ends at spring pruning time. Another strategy is to debud 4 to 6 inches of limb below the terminal bud after bud swell (Photo 7).
The resulting debudded region is relatively free of branches, and free of the canker problems that often show up in this problem area. In addition, timely irrigation and nitrogen application will help young trees to develop scaffold limbs with wide spaced limbs, and fewer potential limb problems.