Dr. Matt Whiting’s new system for growing sweet cherries—nicknamed the UFO—turns convention on its head.
Typically, when establishing a new cherry orchard, growers head back the nursery trees at planting to reduce apical dominance and stimulate branching. Whiting’s Upright Fruiting Offshoots system, however, does not involve heading.
“The nurseries put their resources into growing that tree, and it seems a shame to just whack it back and put it on the ground,” he said.
Whiting, who is cherry horticulturist with Washington State University, has experimented with several ways of growing young trees with the aim of creating a vertical fruiting wall, and thinks the UFO system might be the most economical and efficient. This new system does not require branched nursery stock and takes advantage of all the planting material, he explained. Unpruned whips are planted at an angle so that the trunks grow horizontally, parallel to the ground. At planting, he removes buds on the underside of each trunk where he does not want branches to grow. Shoots on the upper side are trained vertically on a wire trellis as a row of four to six repeating upright fruiting units.
“We want to have a more efficient system and a more systematic way of training and pruning, and everything else that goes into development of these trees,” Whiting explained during a cherry field day at WSU’s Irrigated Agriculture Research and Extension Center in Prosser this summer.
Fill the row
In a trial planted at the center this spring, trees on Gisela 5 rootstocks were spaced six feet apart with the idea that they would be tall enough to fill the row horizontally, with upright shoots spaced 12 inches apart. Trees on the more vigorous G.6 rootstocks are spaced eight feet apart in the rows. Rows are ten feet apart, and Whiting envisions that the fruiting wall will grow about nine feet tall.
Training the lateral shoots vertically takes advantage of the way cherry trees naturally like to grow, he said, as they are apically dominant and tend not to send out many lateral branches.
He planted a few trees on this system in 2006 as a test. The tallest uprights grew up to about three feet high during the first season. During the winter, some dormant pruning was done to invigorate the weaker growth. In the second growing season, growth of the uprights was phenomenal, Whiting said.
In the new trial, Whiting expects the upright branches to have fruiting buds in two years. The system will require aggressive shoot renewal, and he does not anticipate any of the fruiting wood being more than five years old. The only permanent part of the tree will be the original trunk. After they have fruited for a few seasons, the upright shoots will be removed with dormant heading cuts, leaving four- to six-inch stubs from which replacement shoots can grow.
The upright growth is variable, which Whiting sees as a benefit as it creates a natural hierarchy so that not all the shoots need to be removed at the same time. The most vigorous upright shoots will be the first to be renewed.
It will be important to manage the crop on this system, which is based upon unfettered upright growth, Whiting said. Trees on Gisela rootstocks usually require aggressive dormant tipping into one-year-old wood to reduce apical dominance and stimulate branching and the production of new leaves in order to keep the leaf-to-fruit ratio in –balance.
But the UFO system is the opposite, Whiting said. “Don’t touch the upright growth. We basically want to grow poles that don’t have lateral breaks. We want to grow three- to five-year-old poles, fruit them, and take them out.”
Whiting said the crop load must be adjusted to achieve the right balance of leaves and fruit. This could possibly be done with a chemical bloom thinning, mechanical bloom thinning similar to that being tested on peaches, or by green fruit thinning from a platform.
He would not recommend trying this system with trees on Mazzard, other than perhaps with low-vigor, –precocious varieties such as Sweetheart or Chelan.
The replicated trial is also being conducted in six commercial orchards. In a Stemilt Growers, Inc., orchard near Pasco, Washington, the system is being tested with Sweetheart on Mazzard. Whiting envisions that with a more –vigorous rootstock, more upright branches might be trained up from each tree—perhaps six to eight rather than four to six—to dilute the vigor.
WSU graduate student Brett Adams is involved in a project at the Prosser research station to compare the performance of sleeping eyes versus nursery trees in new cherry plantings.
The cherry industry is changing, with the introduction of new varieties and rootstocks and higher-density plantings, Adams noted, but the cost of planting trees on precocious rootstocks for –intensive cherry plantings can be high.
“I know this industry needs to find out how we’re going to put a block of cherries in at three by eight feet and make it affordable for all of us,” he said.
A sleeping eye is a rootstock that has been grown for a season at the nursery and grafted with the scion in the fall. It is dug in the spring and immediately planted out in the orchard, giving the grower the responsibility of training it into a tree. This cuts out the growing of the tree at the nursery and is a cheaper option than a full-grown nursery tree. However, the grower then assumes the risk of losses because of failure of the sleeping eyes to grow, possibly because of virus infection, incompatibility of the rootstock and scion, or just weak growth.
Adams said a nursery’s sole goal is to produce good, uniform trees, but in an orchard, the focus might be different. In the trial, Adams treated the trees and sleeping eyes just as a grower would in an orchard. Overall, there was 17 percent less survival of sleeping eyes than of standard nursery trees of the same rootstock and variety. With Bing on Mazzard, only 60 percent of the sleeping eyes –survived when they were grafted with a virus-infected scion, versus 88 percent of nursery trees with virus-infected material. With virus-free material, the survival rate was 81 percent for sleeping eyes, compared with 97 percent for nursery trees. Adams said he hopes to find the reasons for the losses.
By the second year, however, the sleeping eyes that survived outperformed the nursery trees in their first year in the ground, Adams reported. “There’s a lot more vigor and growth in the sleeping eyes, and I have to assess that situation,” he said.
He believes it could be related to the transplant shock that full-grown trees experience when they are dug from the nursery and planted in the orchard. He will monitor them to find out if the sleeping eyes continue to perform best in –subsequent years.
Although the grower would have to replace the sleeping eyes that didn’t survive, Adams calculates that sleeping eyes would still work out to be less expensive, though not by much. The grower would also need to take into account the cost and availability of labor required for growing the sleeping eyes into trees.