Sweet cherries are borne on flowers at the base of short limbs in the super spindle axe system. (Courtesy Stefano Musacchi)

Sweet cherries are borne on flowers at the base of short limbs in the super spindle axe system. (Courtesy Stefano Musacchi)

Stefano Musacchi, who was hired in 2013 to fill Washington State University’s endowed chair in tree fruit physiology and management, has been one of the world’s active participants in designing and evaluating sweet cherry production systems.

In 2007, he and colleagues Federico Gagliardi and Sara Serra at the University of Bologna in Italy began what would become a seven-year period of observation and data collection on three high-density training systems. The result of their work was reported in a paper published in HortScience in March this year.

The study evaluated performance of ten sweet cherry varieties on Gisela 5 and Gisela 6 rootstocks in the three training systems: spindle, V-system, or super spindle axe (SSA). Only some of the varieties studied are grown in the United States, but, in general, the study produced useful conclusions.

“Our results demonstrated that it is possible to develop a high-density-planted sweet cherry orchard producing a significant yield by the second and third year after planting,” they say. “The SSA and V-systems, in combination with the correct cultivar, guaranteed a high level of production and positively affected fruit quality.”

The V-system and SSA produced higher yields than spindle on both rootstocks, on all the varieties tested.

Generally speaking, low production per tree (7 to 12 pounds) was compensated for by a high number of trees, they reported, and the quality was very high. More than 90 percent of the fruit had a diameter more than 28 mm (9-1/2 row).

“Pruning will be a key factor to minimize wood aging and yield reduction,” they say.

The high-density training systems, particularly the SSA in combination with short-pruning, offers the possibility for orchard mechanization. “For mechanical pruning, the small width of the trees could allow lopping machines to shorten all the one-year-old shoots at four to five buds of length.”

Among the three systems grafted on Gisela 5, trees trained to the spindle system had the highest trunk cross-sectional area, followed by V-system and SSA.

Choice of cultivar was important for yield, sweetness, and cherry size. Different cultivars also respond differently to the different pruning methods, depending on where they bear most of their cherries—on basal buds or spurs.