Lynn Long (left) and grower Dave Meyer discuss pruning strategies in a block of fifth-leaf Chelan trees on the Krymsk 5 rootstock.

Lynn Long (left) and grower Dave Meyer discuss pruning strategies in a block of fifth-leaf Chelan trees on the Krymsk 5 rootstock.

Geraldine Warner

The cherry rootstocks Krymsk 5 and 6 are not so precocious as Gisela rootstocks but more productive than standards such as Mazzard, orchardists are finding. Dave Meyer, a cherry grower in The Dalles, Oregon, has a mature block of Lapins on Krymsk 5 and 6 and Gisela 12 rootstocks. Krymsk 6 is comparable in size to Gisela 6, but K.5 is bigger—closer to G.12, but with less dense fruiting, Meyer reported during a grower tour to his orchard.

Krymsk 5 is an option where a grower might want more precocity and dwarfing than Mazzard but less precocity than a Gisela rootstock, he said. In some situations, the Gisela rootstocks have a tendency to overcrop.

In Meyer’s Lapins block, the average yield from the trees on Krymsk rootstocks is about 8 tons per acre, which Meyer said is low by most people’s standards, but he is happy with fruit quality and size.

Lynn Long, Oregon State University Extension educator, said people are finding that K.5 is not as productive as G.6, but much more productive than Mazzard.

“I think that’s exactly where you want to be on these dwarfing rootstocks,” he said. “You want a tree where you can get the right balance of leaves to fruit. If you have too many fruit, you’ll have small fruit. It’s easier to get that balance with Krymsk 5.”

Long said that Lapins, being a productive variety, is generally grown on Mazzard rootstocks, “but Dave has been successful growing quality year in, year out on a more productive rootstock.”

Meyer said he has Skeena on K.5 and K.6 also. He’s noticed that in years when fruit set is heavy and the cherries would typically grow in clumps, like grapes, the fruit on trees on Krymsk rootstocks is more spread out, ­making it easier to pick the fruit without damage.

He has Chelan on Colt, Mazzard, K.5, and K.6, and prefers K.5 with that variety. The trees grow as quickly as trees on Mazzard or Colt for the first few years, but then stop growing and maintain their size. With the central leader system, K.5 are more productive than on the other rootstocks, yielding a small crop in the third leaf and a good crop in the fourth, Meyer said.

Long said another good combination is K.6 with Regina, an unproductive variety, because the rootstock increases productivity.

Both K.5 and K.6 tend to sucker, but it’s not unmanageable, Meyer reported. The Krymsk rootstocks are reportedly sensitive to prune dwarf and prunus necrotic ring spot viruses, but Meyer had not seen any evidence of them in his trees.

Long said hypersensitivity to a virus can be a positive thing because the infected tree can die within a year before the virus can be transmitted by insects or root grafts to neighboring trees. A tree on Mazzard that becomes infected will decline slowly, giving the virus an opportunity to spread.

Meyer said he suspects that the Krymsk rootstocks, which originated in Russia, are better able to withstand harsh conditions, whether extreme heat or cold. Meyer noted that on hot afternoons in August or September, if the trees are stressed, the leaves on Gisela rootstocks often seem cupped, but leaves on Krymsk lay flat. It’s been reported that K.6 performs better than G.6 in California’s hot areas. Long said this is based just on grower observations so far and has not been researched.

Training systems

Meyer uses the central leader, steep leader, and Kym Green Bush systems.

Long said a trial he conducted at Greg Johnson’s orchard in The Dalles indicates that central leader trees come into production earliest because of less pruning, but by the fifth leaf, the KGB trees outyield the other systems. Pickers are able to pick more fruit per minute on the KGB system than in the other systems because the KGB is a true pedestrian orchard.

“Any time you have to deal with a ladder, it slows your picker down,” he said. “Their productivity on the KGB was higher.”

Long also found in the Johnson trial that in the early stages there was more labor involved in training the central leader than the other two systems.

Long provided some guidance on how to prune trees on productive rootstocks. Any wood that is weak or below horizontal should be removed in the dormant season because they typically will tend to overcrop with small cherries and there will be no new growth at the tip of the shoot. New leaves are needed in order to size the fruit, he explained. Otherwise, the shoot will draw resources from the rest of the tree.

One-year-old wood should be tipped annually during the dormant season to reduce the coming season’s production and encourage branching and growth of new leaves.  Spurs should be renewed by cutting into older wood because the best quality fruit will be grown on young spurs. No spurs should be older than five years, so about 20 percent of the wood should be renewed every year, whether the system is the KGB, central leader, or Upright Fruiting Offshoots (UFO), Long said.

Branches in the top of the tree should be cut in summer, after harvest, to reduce the vigor of the top. The rest of the cuts are done during the dormant season to ­invigorate the bottom of the tree.

However, Meyer said with his Chelan trees, which lack vigor, he plans to cut the tops back in the winter. “With any other variety I would come in postharvest and take the tops down,” he said. “With the Chelan, I will probably winter top them because of the lack of vigor.”

Long has written an article on how to prune cherry trees on productive rootstocks, which can be downloaded from http://ir.library.oregonstate.edu/xmlui/handle/1957/20783.