Issue link: http://read.dmtmag.com/i/481870
www.goodfruit.com GOOD FRUIT GROWER APRIL 1, 2015 35 To develop the tree system, Hirst worked with Park and Kak, in Purdue's department of electrical and computer engineering, who are building digital 3-D models of trees and designing software. "The challenge is to accurately construct 3-D models of trees and vines and program that in such a way that the computer can determine the optimal points to prune. Our goal is to make this work at a speed that makes sense fi nancially for growers," Park says. As a fi rst step to automated pruning of apples, there have to be some rules to prune by. Schupp, the Penn State pomologist, set to work to provide those. Although pruning is often considered an art, not a science, Schupp was surprised how easy it was to develop rules. He made eight rules—steps that a human pruner would take in pruning a tree. Then, examining them, he found that four rules really covered it all pretty well. And, on further examination, he wrote one rule that he believes covers 70 percent of the job. First, however, he had to select a tree to prune. "I chose the tall spindle single axis system," he said. "It is the world's standard tree today." Besides its early, high productivity and top quality fruit, growers like the tall spindle system because it makes pruning easier with its renewal pruning concept, in which larger branches are removed completely, almost on a schedule. Here are the eight rules as Schupp originally wrote them: 1. Once the leader reaches 14 feet, head it to a short side branch by cutting into two- and three-year-old wood to maintain a tree height of 11 to 12 feet. 2. Maintain a narrow cone shape by thinning out shoots that are more than 30 inches long in the top. 3. Remove any secondary limb when its diameter becomes more than half the diameter of the leader or more than 1.5 inches in diameter, whichever comes fi rst. 4. Remove two, three, or four (your choice) of the larg- est side branches remaining, leaving a short duckbill stub. 5. Remove all damaged or diseased limbs. 6. Thin otherwise good branches, spacing them out to reduce the number of secondary branches to 30 to 60, depending on your yield expectations. 7. Remove all other vertical shoots with an angle of less than 40 degrees. 8. Prune each remaining side branch to a single axis, either by thinning away tertiary branches that are more than half the diameter of the secondary branch or by stub- bing the drooping limb back to a new axis. This step also eliminates pendant limbs. After looking at the rules, Schupp noted that 70 percent of the pruning could be done following one rule only, rule number 4: Remove the two to four largest limbs. Add rule number 7, taking out vertical growing limbs, and the job is 90 percent done, he said. He did not think that rule number 1 could be trusted to a robot. ONLINE Information about the project can be found at the website pruningautomation.com PHOTOS COURTESY VISION ROBOTICS A view of the interior of the robotic vine pruner shows the robotic arms, with cameras, that move the clippers.