Grower Focus Starting to Sharpen on Precision Pruning of Apples

When Terence Robinson speaks of precision pruning, he does so with passion, writes Thomas Skernivitz at Growing Produce. In the end, the Applied Fruit Crop Physiologist from Cornell University leaves nothing unsaid, even if it takes some reiteration.

“I want to introduce two physiological concepts that I don’t think that I’ve explained that well in the past,” Robinson told attendees of the annual Cornell NYS Tree Fruit Conference. “And I hope that this will help you understand why we push precision pruning so hard.”

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CONCEPT NO. 1

In the spring, at green tip, the tree mobilizes reserves of carbohydrates and hormones, particularly cytokinins from the roots, and moves them up the tree. Meanwhile, the tree, with a spring flush of growth, takes in primarily nitrogen along with other nutrients from the soil and transports them up the tree.

When the tree has an excessive number of buds, that amount of cytokinin, carbohydrates, and nitrogen transported to the top is divided among numerous buds, leaving each bud with less than the optimal level of nitrogen, carbohydrates, and cytokinins.

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“That results in weak buds,” Robinson said, and weak buds have low fruit set, produce small fruit, and are more biennial. But “if we can reduce the bud number through pruning …” he pondered.

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Such pruning, again, would have to be done before green tip. Done later, the tree has already pushed many of its reserves into the soon-to-be eliminated buds. While waiting to prune until after growth starts would be good horticultural strategy to weaken the vigor in overly vigorous trees, with trees that are mature and low in vigor — which is often the case with ‘Gala’, Robinson noted — it results in buds that already are weak in getting reserves and then cutting them off.

Therefore, the pruning for ‘Gala’ has to be done before green tip, Robinson said. “If that’s done, each of the remaining buds — those 170 buds that we’re going to leave — will get more nitrogen, more carbohydrates, and more cytokinins, resulting in more vigorous buds, larger fruit size, and less bienniality.”

Robinson’s mention of 170 buds is a benchmark that he frequently emphasizes. Specifically, he recommends that precision pruning — the process of reducing the number of flower buds to a predetermined number through pruning while using the rules of tall spindle pruning and then spur extinction pruning — results in maximums of 170 flowering spurs for Tall Spindle ‘Gala’ and 131 in Tall Spindle ‘Honeycrisp’.

Continue reading at Growing Produce.

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