2017 ASHS Annual Conference

Renewal of sweet cherry (Prunus avium L.) fruiting wood to maintain optimal canopy light interception and distribution is key for high productivity and fruit quality throughout the life of an orchard. Typical renewal involves replacement of 10 to 20% of the tree canopy annually by removing one to several of the largest branches. In a mature orchard, this renewal process is subject to competition between sun-exposed fruiting sites and interior canopy renewal sites that intercept less light and compete poorly for translocated photoassimilates, often resulting in poor renewal growth. This is particularly problematic for high density orchards that utilize rootstocks selected for reduced vigor and high productivity. Renewal of canopy fruiting sites on a whole tree basis, by annually removing the entire secondary canopy structure of 10 to 20% of the trees in the orchard, is an alternative renewal method that eliminates the competitive inhibition of shoot regrowth while promoting a proportional level of overall orchard renewal. This study explores the initial response of sweet cherry trees on various training systems and size-controlling rootstocks to whole tree renewal. Four training systems were studied: Tall Spindle Axe (TSA), Super Slender Axe (SSA), Upright Fruiting Offshoots (UFO), and Kym Green Bush (KGB). A preliminary study in 2015 with UFO-trained ‘Rainier’ on dwarfing Gisela 3 showed the best regrowth response of whole tree or standard selective renewal cuts when made at bloom. In 2016, whole tree renewal of the four systems was studied with ‘Benton’ on three rootstocks : Gisela 3, semi-dwarfing Gisela 5, and semi-vigorous Gisela 6. During bloom, all fruit-bearing components of the canopy were pruned back to stubs close to the permanent structure (usually the trunk or cordon, depending on system). Regrowth occurred from May to September, and renewal shoot data were taken in December. Shoot number and average shoot length tended to be inversely proportional when comparing the canopy architectures: TSA resulted in the most new shoots, while KGB and UFO had the longest average shoot length. Across all training systems, Gisela 6 resulted in both the highest number of new shoots and length per shoot. Vigorous regrowth often resulted in sylleptic lateral shoots arising on the renewed proleptic shoots, which may have significant implications for the different training systems. The results indicate that each canopy system-rootstock combination responded with enough growth to make whole tree renewal a potential option for rapid, relatively uniform renewal of fruiting sites.