Issue link: http://read.dmtmag.com/i/481870
36 APRIL 1, 2015 GOOD FRUIT GROWER www.goodfruit.com "Don't let a robot touch that leader," he said. "Do it manually." "Will a robot be capable of making a bevel-shaped stub cut?" someone asked, at which time Schupp answered, "Does it matter?" There is no research, he said, to show that a tree makes a better replacement branch under a bevel, or Dutch cut, than under or above a square stub cut. "Some Dutch guy back in 1968 said it was better, but presented no data, and we just went with it. Does it mat- ter? The key is to leave the collar and a limb will grow," Schupp said. Last first Schupp noted that pruning severity also needs to be addressed, and that starts with the number of large limbs selected for removal. The idea is to tell the machine (or person) to remove the largest limb fi rst and then move to the next largest limb, in order. He conducted research to determine how yield and fruit quality respond to pruning. He concluded that a limb-to-trunk-size ratio of 1.25 seemed ideal. In other words, taking the trunk cross-sectional area and increasing it 25 percent gives a number that is the ideal cross-sectional area of all the limbs growing off the trunk. The more limbs that are removed, the greater the prun- ing severity, and the lower the ratio. Yield is reduced when the number gets closer to 1, and fruit size and quality is reduced when the number gets up to 1.75, Schupp found. That ratio still needs to be modifi ed, he said, because as trees get older the trunk will become larger, but the limbs should not be allowed to become permanent scaffolds. So the ratio will increase as the trunk gets larger. Modeling the tree Elfi ky, the Purdue engineer, explained what her team did after Schupp gave them the pruning rules. They used sensors to determine the shape of the tree, the location of its limbs, and the size of the limbs and leaders, and made a model of the tree. As it turned out, a few cheap sensors, costing about $200 each, were capable of generating a computer pic- ture of the tree. Telling the machine to remove the three largest limbs was simple. If a machine for pruning trees is developed along the same lines as the Vision Robotics grape pruner, the machine will likely move from one tree to another, scan- ning the next tree in line as it moves. Then it will stop, the arms will move, the shears that are its "hands" will make the cuts, and the machine will move to the next tree, scanning it as it moves. "This research has caused us to examine things we never really thought about," Hirst said. A seasoned horticulturist with 30 years experience, he recalled the hundreds of pruning demonstrations where one expert would make cuts and explain why, and another would do something completely different. Hirst thinks that Schupp's pruning rules will not only help robots, they will help humans. You can do 70 percent of the pruning and get 90 percent of the benefi t by making 8 to 10 cuts, Schupp said. People or robots can do that. • Pruning rules Jim Schupp has reduced pruning to the following four basic rules, in order: 1. Remove all limbs larger than the calculated maximum branch diameter with a renewal cut 2. Remove all pendant and upright limbs 3. Thin out remaining horizontal limbs to 8- or 9-per-meter of spindle 4. Prune each remaining limb to a single horizontal axis. "Don't let a robot touch that leader. Do it manually." —Jim Schupp