On February 5, 2018 Stefano Musacchi, WSU Endowed Chair of Horticulture and Bob Gix, Blue Star Growers discussed pruning horticulture with fifty-four growers at a WSU Extension Field Day in Yakima, WA. The discussion focused on Bartlett in higher density systems. The goal was to discuss horticultural possibilities, options and creative solutions. Then growers can decide what is practical and how to implement.
Here we will summarize three main discussions from the field day: minimizing shade, angle for V trellis pears, and renovating fruiting wood. Join us February 19 for another pear field day in Cashmere.
Minimizing shade: When our goal is fruit, minimizing shade is important. Buds will only differentiate to form flower buds if there is more than 30% of the ambient light. “Light is the only thing we don’t pay for,” Musacchi reminded us, “How you use the light is critical.” Taking out large branches that produce too much shade can help manage this challenge. The angle of the canopy will also designate the shadiness in a V system.
Angle in V trellised Pears: Pears have strong apical dominance. If we grow them at too flat of an angle the trees will become ‘angry’ and produce many suckers. Leaders with many suckers can become exhausted and have few flower buds. Also canopies with too flat of an angle will reduce the light, sometimes to the point where there are only a few hours per day with adequate light. The result will be a concentration of the flower buds at the top of the tree with little fruiting wood down lower. “If we have too flat of an angle the trees behave like old trees,” Musacchi explained. Pears on V trellis should be planted with an angle of only 10˚ from vertical.
Renovating for fruiting wood: In this situation where there is an area lower in the canopy with insufficient fruiting wood and flower buds, Musacchi suggests a three-year cycle pruning strategy: year 1) remove bigger suckers, prepare new fruiting branches by bending and tipping, prune this year’s fruiting wood, one big branch in the top can be removed, and reduce the height on one side of the angle canopy; year 2) continuing to remove suckers, prepare new fruiting branches, one old branch in the top of tree can be removed and reduce the height of the other side of angle canopy; year 3) start to rotate old branches and prune the one removed with a stub to produce new shoots. “It takes 3-4 years to transition from one style to another,” Musacchi explained.
- Remove big suckers: Larger suckers will exhaust the fruiting wood and should be removed.
- Prepare fruiting branches: Bartlett produces on two-year-old wood. In order to build fruiting wood tie one-year-old branches to a 45-degree angle. Tip, or ‘click’ performing a heading cut on the tip of the one-year old branch to break apical dominance and force the branch to form one to two shoots. The following year you can keep the branches that you want. This heading cut helps keep the buds alive. It also keeps the branch from bending down which might create blind wood. Keep in mind that heading cuts can be used for two different functions. This cut at the end of the branch is a training cut. A heading cut lower on the branch can also be used as a production cut which forces buds to swell to form fruit.
- Prune this year’s fruiting wood: Perform your standard detail pruning. This may include using ‘click’, or heading cuts which leave two to three buds forcing these buds to swell by breaking apical dominance. A short cut right above a bud will force the bud to swell. Simplify the structure taking out dead wood.
- Reduce the height of the trees on one side to allow light to penetrate deeper in the canopy. In this situation with a V cutting one side one year and then the other the next may help balance the transition with maintaining yield in the short term.
- Summer pruning can be utilized to reduce the number of suckers produced inside the V. Suckers can be pulled out by hand. Be careful to perform this punning when there is no risk of fire blight infection.
- Take out one large branch in the top part of the tree and reduce the tree height. Now that there is smaller diameter wood to replace old branches that are too large. Not all of this large wood should be removed at once.
- Reduce the height of the trees on the other side to complete height reduction and allow light to penetrate deeper in the canopy.
- Top: Maintain the top pruned with the click technique and define a lower height of your tree to allow more light to penetrate deeper in the canopy.
- Start to rotate old branches and prune the one removed with a stub to produce new shoots.
Join us February 19 for the next pruning and horticulture discussion in Cashmere WA. http://treefruit.wsu.edu/event/pear-pruning-demo-northern-site/
Tree Fruit Extension Specialist