Issue link: http://read.dmtmag.com/i/543863
www.goodfruit.com Good Fruit Grower AUGUST 2015 49 during mechanical pruning, it reduces the total amount of carbohydrate in the tree, but it also exposes the fruit to more light. A fruiting wall is typically only two feet deep. Narrow canopies can be very effi cient, Musacchi said. "We assume that all the leaves have the same efficiency, but that's not true. When a leaf develops in the shade, it never becomes effi cient like a leaf that develops in the sun, and you can have a lot of leaves, but the effi ciency of your leaves is not full." When branches are pruned to main- tain them within the same space, they can be effi cient for a long time, he said. Timing When converting a slender spindle system to a fruiting wall, mechanical pruning is done in winter to avoid com- promising the crop the following season. It can be combined with an application of the growth regulator Apogee (prohexadi- one calcium) to prevent regrowth of long shoots. As a maintenance operation, mechan- ical pruning is done in early summer, as needed. It does not have to be done every year. Timing of summer pruning is typically when the shoots have grown 12 leaves (which in Washington is in early June) to stimulate induction of flower buds for the following year. Musacchi and Lewis are also testing a slightly later timing when the shoots have 20 leaves (June 15-20), which would give growers a wider time frame for getting the job done. "In our light conditions here, I would like to see if we can play a little bit because the shoots are growing fast and we can't do everything at the twelfth leaf," Musacchi said. "I would like to know how many days we have available." Mechanical pruning cuts off the tips of the branches, which removes their inherent apical dominance. It has a similar effect to a hand-pruning cut that Musacchi calls a "tira savia." It's a short cut made in one-year-old wood, leaving two to three vegetative buds. This helps to stimulate bud break closer to the trunk, or axe, of the tree and minimize blind wood. It also improves fruit quality because buds that are closer to the trunk produce larger fruit. "We want short branches with a lot of spurs," Musacchi said, noting that the ideal is to start off with a fruiting wall that has short branches, rather than convert an existing orchard. Hand pruning is needed immediately after hedging because the vertical blades of the machine can't cut across vertical branches or branches oriented parallel with the tree row. Upright or pendant branches have to be removed by hand, but the cost is still less than if the orchard was fully pruned by hand. Any fruit damaged during mechani- cal pruning can be targeted for removal during hand thinning. Musacchi said not all orchards are suited to mechanical pruning at the same time. It should not be done if the trees are too weak. "You have to evaluate when your orchard is ready to be pruned mechan- ically, because if you don't completely fi ll the space, you can reduce your crop load," he warned. "But, at the same time, when you start to prune, you reduce the size of the branches, and you have some help to complete the structure in the upper part of the canopy." He does not recommend mechanical pruning on angled canopies. The hedger can only prune the outside of the trees and not the wood in the middle of the V, so the effect is minimal. "It doesn't justify the cost of running the equipment through," he said. The three-year project, which also includes trials with mechanical pruning of cherries, is funded by the Washington Tree Fruit Research Commission and is now in its second year. • NEXT ISSUE See how Italian horticulturist Dr. Stefano Musacchi is introducing his concept of "dynamic pruning" to Bartlett pear growers in Washington's Wenatchee Valley. Before After PHOTOS COURTESY KAREN LEWIS, WSU "You have to evaluate when your orchard is ready to be pruned mechanically, because if you don't completely �ill the space you can reduce your crop load." —Stefano Musacchi Mechanical pruning: How it looks