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The tall spindle system, with tree densities around 1,000 to 1,500 trees per acre, is highly competitive and productive and has potential for mechanical harvesting and pruning.

The tall spindle system, with tree densities around 1,000 to 1,500 trees per acre, is highly competitive and productive and has potential for mechanical harvesting and pruning.

Dr. Terence Robinson is on a quest to find apple orchard systems that will improve the profitability and competitive position of the U.S. tree fruit grower. He recently conducted an economic analysis of existing orchard systems and found that the tall spindle system may be the most profitable for New York and other eastern region orchardists.

“Unfortunately, the most competitive apple system can’t be done on existing orchard systems and has to be done on replant or new situations,” said Robinson, Cornell University horticulturist, while sharing results of his research with growers attending the Great Lakes Fruit, Vegetable, and Farm Market Expo in Grand Rapids, Michigan.

There has been a steady evolution in planting systems, he observed. “Since the 1960s, the industry has made tremendous leaps forward as growers moved away from large processing trees to more efficient orchard systems like the central leader.”

In the 1970s and early 1980s, many growers planted more pedestrian-style orchards with compact trees on M.9 rootstock, 400 to 600 trees per acre, to achieve early yields, though this system had problems with moderate yields.

Higher tree densities of 500 to 700 trees were popular in the late 1980s as growers moved back to taller trees on the vertical axis, Robinson said. But this system had challenges of managing the tops of trees, and limb renewal was needed to maintain tree shape and improve light exposure to the lower canopy. “However, this was a major leap towards improving yields,” he said.

The super spindle system, which became popular with orchardists in the 1990s, had tree densities as high as 5,000 per acre, although most were around 2,000 to 2,200.

“In my younger years, I thought that such a high number of trees was impossible to manage,” he said. “The problem with the super spindle system was the economics. It’s so expensive to plant 2,000 trees per acre except for those who grow their own trees.”

An amalgamation of several orchard trends gave rise to a new system in the late 1990s that he calls the tall spindle system. It incorporates aspects of the slender spindle, vertical axis, and super spindle, achieving early high yields, high sustained yields, and excellent fruit quality, while moderating the initial tree investment. Tree densities are 1,000 to 1,500 trees per acre.

Economic analysis

Robinson studied the economic differences between five apple systems (slender pyramid, vertical axis, slender vertical axis, tall spindle, and super spindle) with tree densities ranging from 340 trees per acre to 2,200. Four different varieties were planted on the trees.

In general, his results showed that the higher the density, the greater the yield, with the highest density producing three times the yields of the lowest density. But the greater the density, the greater the planting and investment costs. Although the higher density systems generate higher early yields and higher cumulative yields, he found there is a law of diminishing returns when it comes to tree density. Very high tree densities were not more profitable than more moderate densities.

“You can go beyond the optimum for density. The super spindle probably goes beyond,” Robinson said.

When the net present value of the accumulated profit over 20 years was calculated per unit of land area, the greatest profitability was at a tree density of 1,000 trees per acre. The profit declined for the super spindle, Robinson said, pointing out the substantial economic impact from the materials needed for tree support. “You just can’t afford to put a pipe at each tree as needed in the super spindle system.”

He found that by using an alternative method to evaluate profitability that used net present value per unit of capital invested compared to per unit of land area, the optimum tree density was lower—around 900—regardless of whether a four-wire trellis or metal stake plus single-wire trellis were used to support the trees.

The study also illustrated the profitability and planting density relationships between tree price and trellis cost. At low planting densities, there was little effect from tree prices, but the opposite is true at high densities.

“In general, our economic study indicated an optimum tree density of 1,000 to 1,200 trees per acre unless fruit price was very high,” Robinson stated. “This range of tree densities led to the development of a training system for this density we call the tall spindle.”

Tall spindle

Based on the economic data and planting trials in northern New York, Robinson believes that the tall spindle system will help growers improve profitability and stay competitive.

“What I’m suggesting is that growers use three-feet-wide row spacing—not wider than 3.5 feet—and grow trees three meters tall,” he said, adding that there are no permanent branches in this system. Highly feathered trees are needed, with the feathers tied below horizontal at planting to prevent branches becoming scaffold branches. Some crop is picked in the second year.

“The tall spindle is the only system that achieved 300 bushels per acre in year three and the only one to achieve 1,000 bushels per acre over five years,” he said, adding that cumulative yield was the greatest with the tall spindle of all five systems in the trial.

He noted that in the past, it was difficult to get high-quality feathered trees from nurseries. But nurseries are now growing highly feathered, high-quality trees that require little pruning and minimal branch tying.

It is important to plant the tall spindle system on dwarfing rootstocks, such as Malling 9, Budagovsky 9, or the new fireblight-resistant Geneva rootstocks (G.11, G.16, or G.41). Weaker apple varieties, like Honeycrisp, should be planted on the more vigorous rootstock clones; weaker rootstock clones work well with vigorous scion varieties on virgin soil.

In New York State trials, tall spindle orchards have shown impressive results, with McIntosh and Honeycrisp yields twice those of the vertical axis.

Robinson acknowledged that the high-quality nursery trees used in the tall spindle are expensive to plant, but said there might be opportunities to reduce planting costs by using bench grafts or sleeping eyes. However, closer management is then needed during the orchard establishment period.