Focus on Stubs for Peach Tree Training

It is easy for peach trees to get out of control, with the canopy expanding out and upward over the years. Shading in the thick canopy inhibits red blush development and reduces bud hardiness. The use of stubs, a fundamental unit in peach and nectarine trees, is an important and useful tool to help peach trees be productive and keep fruit quality high.

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A stub is simply a one-year-old or younger branch that has been headed (stubbed) down to 2 to 5 inches in length. A young, vigorous branch cut in this fashion readily develops new shoots, some used for fruit production and some for stubbing, continuing the cycle. Shoots left for fruit production are often called “hangers” because fruit hang from them.

The concept of stub pruning has been around for many years, initially championed by University of California researchers for use in V and quad-training systems. In regions with shorter growing seasons, stubs are usually cut during spring pruning. In the longer California growing season, stub cuts can be made postharvest and still have time for sufficient growth in the same season.

A key point is that the stub should be at least 1/3 inch in diameter and have at least one, or preferably two or three points of green growth. Candidate shoots with no evidence of growth and/or small caliper will often stop growing and die. It is best to wait in the spring until growth starts in order to choose the most promising shoots to cut.

The stubbing process is tied to the development of the overall tree structure. The basic tree structure, regardless of the training system, develops during the three to four years following planting. During this time, the scaffolds grow 2 to 3 feet in length each year until they reach mature height.

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There is an approximately two-year window to establish stubs on a new section of scaffold before it becomes reluctant to sprout new side limbs. It may take two growing seasons to develop enough functional stubs in a scaffold section. Learning how to see stubs, understanding how and when to start them, and maintaining them can be a challenge to the novice tree trainer.

Peach and nectarine are somewhat unique among stone fruit in that fruit are formed exclusively on last year’s growth. Most other stone fruit types, such as plum, apricot, and cherry, develop short spurs that produce fruit over several years. As peach and nectarine limbs age, they lose the tendency to generate new growth, and fruiting potential drops unless a structured system such as stubs is put in place. A general goal in setting up stubs on a new scaffold is to have at least one, and preferably two stub systems, per foot of scaffold.

A great advantage of stubbing is that the fruiting structures are kept close to the scaffolds, which helps to provide good light penetration throughout the tree. This can be envisioned as a narrow cylinder of fruiting structures around the scaffold. Ideally, this narrow cylinder should extend to the top of the scaffold. Side limbs high on the scaffold that have too much vigor should be removed before they inhibit stub renewal growth lower on the scaffold.

Another advantage of the stub-pruning approach is that renewal pruning on the stub system calls for cuts to small-diameter, relatively young wood. Small cuts on side branches generally mean less risk of Leucostoma canker, a disease favored by large-diameter cuts close to the scaffold.

Each tree training system has its own arrangement of support structures and fruiting cylinders. For example, a pedestrian open-center tree with near horizontal scaffolds has a secondary set of upright limbs populated with stubs. Quad and Y (V) systems have scaffolds at 25- to 40-degree angles from the vertical, and the stubs are arranged along the scaffolds. Regardless of the training system, starting with stubs helps to anchor the fruiting wood close to the scaffolds for future crops.

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