Good Fruit Grower

May 1

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photo courtesy of dan lagasse FRUITING WALL principles T he tall spindle orchard design that is being so steadfastly encouraged by researchers—and adopted by growers—in the eastern United States came about from the discovery of several important principles. In the 30 years he has been working to develop the tall spindle system, Cornell University's Dr. Terence Robinson said he was guided by five principles: Studies on light interception showed that the highest yields required that trees intercept 70 to 75 percent of the light. Growers who wanted pedestrian orchards of around eight feet tall couldn't achieve that unless they went to very narrow alleys that are too narrow for current machinery. That meant trees need to be taller, about 12 feet, and the alley width about 90 percent of that. Studies on light distribution showed that thick canopies have too much heavily shaded area which results in poor quality fruit. "This has led the effort to narrow the canopy of modern orchards to not more than three feet deep (four to six feet from side to side)," he said. The need for early high yield to pay back the initial orchard investment led to studies on how to improve early yield. This resulted in the use of feathered trees, higher tree densities, irrigation and fertigation to maximize early tree growth, minimal pruning (especially not heading the leader), and branch bending to induce early cropping. Simple and thin tree canopies are more adaptable to mechanization, and the tall spindle design made it easier to use platforms to improve labor efficiency. The process of renewal pruning also reduced labor cost by simplifying and speeding up the pruning process. Tree density is subject to the law of diminishing returns. At some point the cost of additional trees is greater than the yield gain. Cornell economic studies put this number at around 1,000 trees per acre with tree costs around $7 each, but above 2,000 trees when tree cost is $2 a tree. —R. Lehnert 1 2 3 Dan LaGasse of LaGasse Iron Works built this hedger, which was purchased by Cornell University and used in the development of fruiting walls at five orchards in New York State. In these pictures at Lamont Farms last July, Terence Robinson ran the machine as it sheared and formed the walls on Rod Farrow's trees. the shoots and thus had a small effect on light distribution in the canopy," he said. "The sidewall shearing treatments did not induce vigorous shoot regrowth regardless of the timing." Robinson said it will take two more years of research to look for negative effects, but if sidewall shearing in the summer can reduce summer pruning costs by 95 percent and improve fruit color without negative effects on return bloom or vigorous growth response, it will also have a significant impact on orchard profitability. "A long-term strategy that we envision is to use annual sidewall shearing of tall spindle trees for three successive years with no other dormant pruning, but in the third year to add a dormant winter corrective pruning to remove limbs that have become large and are causing internal canopy shading and poor fruit quality." Robinson has a friendly rivalry with New York grower Rod Farrow, who uses the slender spindle design, planting more than 2,000 trees per acre two feet apart in the row. Robinson said economic analysis shows the tree cost of slender spindle, where trees are planted two feet apart, is too high unless trees are cheap. Farrow grows his own trees, so his tree costs are less, and the system does produce higher yields than Robinson's tall spindle design. "In general, our economic study indicated an optimum density of 1,000 trees per acre unless fruit price was very high and tree cost was very low," he said. Tree density can vary from a high of 1,452 trees per acre (3 by 10 feet) to a low of 908 trees per acre (4 by 12 feet). Proper density depends on vigor of the variety, vigor of the rootstock, and soil strength, he said. That is a complex interaction. • 4 5 GOOD FRUIT GROWER May 1, 2013 25

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