Growth of unpruned June budded 'Chandler' walnut on clonal Paradox rootstock

J. Hasey, B. Lampinen, L. Milliron, C. Beumel
California walnut growers have several nursery product options available including seedling or clonal rootstock, or finished bareroot one-year old June buds or two-year old nursery grafted trees. Typically, after planting, rootstock or finished trees are cut back to three to six buds and trained to a single leader (trunk) during the first leaf. The primary scaffolds develop during the second leaf and secondary scaffolds during the third leaf. June budded ‘Chandler’ walnut trees were grown for one year in the nursery on ‘VX211’, ‘Vlach’ and ‘RX1’ clonal Paradox rootstocks. Trees were left unheaded when they were dug from the nursery. Growth is being compared in a large replicated trial that was planted in February 2015 in Sutter County, California. Trees were not headed at planting or during first or second dormant season. Tree growth characteristics were noted and rootstock circumference was measured in the fall each year and scions measured in 2017. Midday canopy photosynthetically active radiation interception was measured in 2017. Unheaded June budded ‘Chandler’ trees on clonal Paradox rootstocks produced functional primary branches during the first leaf. By the end of the second leaf, trees had a well-developed structure much more advanced than a normal two-year old tree. Trees were mechanically harvested and produced high yields in the third leaf with ‘RX1’ producing significantly higher yields than the other rootstocks. Rootstock circumference for ‘VX211’ was significantly greater than ‘Vlach’ which was significantly greater than ‘RX1’ 2015 through 2017. However in 2017, scion to rootstock ratio was significantly higher for ‘RX1’ compared to ‘VX211’. Using unheaded June buds only grown one year in the nursery with no heading in the first or second dormant periods, allows earlier tree development reducing costs of orchard development while producing quicker returns.
Hasey, J., Lampinen, B., Milliron, L. and Beumel, C. (2021). Growth of unpruned June budded 'Chandler' walnut on clonal Paradox rootstock. Acta Hortic. 1318, 109-114
DOI: 10.17660/ActaHortic.2021.1318.17
'VX211', 'RX1', 'Vlach', unheaded, PAR, SWP, micropropagation

Acta Horticulturae