The back story
Tart cherries don’t need to be grown on big trees.
After the fall of communism in Eastern Europe and the breach of the Berlin Wall in 1989, countries like East Germany and Poland were re-integrated into a world where machine technology was much preferred to human labor.
In some cases, in the process of “catching up” with the West, they actually gained an opportunity to “jump ahead.” They abandoned hand harvest and began using technology growers in the United States are just now discovering.
“Tart cherry growers in Poland and East Germany never had trunk shakers in a big way,” said Dr. Amy Iezzoni, tart cherry breeder at Michigan State University. “Since they relied on hand labor for harvest, they had small trees that were close together. These turned out to be the perfect orchards for over-the-row harvesting.”
Today, cherry growers there harvest their cherries using machines like those used to harvest blueberries, currants, and grapes.
Meanwhile, tart cherry growers in the United States are “stuck” with the old trunk-shaker harvesting technology. That technology came into the tart cherry industry in the 1960s. It is still in use more than 40 years later.
Short and bushy
“It is true that the European Schattenmorelle tart cherry tree is a shorter, less vigorous tree than the Montmorency tart cherry grown in the U.S.,” Iezzoni said, “But if you take the trunk off the Montmorency, it’s a bush. If you don’t prune it to grow a trunk, it will be a short, bushy tree.”
The reason for growing a trunk is so one can use a trunk shaker, but it also makes the orchard less profitable because it takes five years or more to grow the trunk. “If you grow it as a bush, it will not take the time it takes to establish it as a tree,” Iezzoni said.
Iezzoni’s work has been both with breeding new rootstocks and also with breeding new varieties, especially varieties that would be resistant to cherry leaf spot. But she is not convinced that a better rootstock is necessary to grow shorter Montmorency cherries that would be of a size conducive to an over-the-row harvesting system such as the one she, Dr. Ron Perry, and other MSU horticulturists are working to develop.
One critical part of changing rootstocks to make trees smaller and more precocious is that the new rootstock must not reduce cherry fruit size. That is often a problem with stone fruits, and is one reason why rootstocks are not more widely used with peaches. Her research work so far looks like that won’t be a problem with tart cherries.
Iezzoni is working on a project to develop rootstocks for sweet and tart cherries, and a series of them is being tested at the Washington State University Roza farm at Prosser, at the University of Oregon, and in test plantings at two Michigan horticultural research stations, one in Traverse City, and the other at Clarksville. She is working in the last year of the five-year project funded by Washington and Oregon.
“We have a handful of rootstocks that are as precocious and dwarfing as Gisela 6 and some as much as Gisela 5,” she said. These new rootstocks will help growers move to over-the-row harvesting.