Growth of unpruned June budded 'Chandler' walnut on clonal Paradox rootstock
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
'VX211', 'RX1', 'Vlach', unheaded, PAR, SWP, micropropagation