UC Davis

Annual production costs for peaches (Prunus persica) grown in California are heavily dependent on the costs of labor for pruning, fruit thinning, and harvest, which is done from ladders because of large tree size (DeJong et al., 1999). To reduce production costs, dwarfing rootstocks have been developed which allow for the establishment of commercially viable orchards that eliminate need for ladders in orchard management. New dwarfing rootstocks for peach must reduce vigor, be graft compatible, and give good fruit production without reduction of fruit size and quality (Reighard, 2002). In April 2015, an orchard system trial was established at the University of California Kearney Agricultural Center, Parlier, CA. The research block consisted of two peach [Prunus persica (L.) Batsch] scion cultivars June Flame (early bearing cultivar) and August Flame (late bearing cultivar) grafted onto three different rootstock genotypes: HBOK 27(Controller 6, moderately dwarfing), P-30-135 (Controller 9, slightly dwarfing), and Nemaguard (CA commercial standard, vigorous). Controller 6 was used in two of four planting/pruning systems, each planting/pruning system had three replications per cultivar. Controller 6 systems were referred to as C-6 V and C-6 Quad. C-6 V was a high-density planting with an in-row spacing of 1.2m (1800 trees/hectare) and trained to the KAC-V perpendicular V system (DeJong et al., 1994). The C-6 Quad system was pruned to a Quad V with a larger in-row spacing of 2.4 m (895 trees/hectare). The Controller 9 Quad system (C-9 Quad) was identical to the C-6 Quad system with the only difference being their rootstock. Between-row spacing was 4.6m in all systems with size-controlling rootstocks. Nemaguard (Nema Quad) was used as the commercial standard rootstock with a planting density of 2.4m in-row spacing and 5.5m between-row spacing (750 trees/hectare). Systems with size-controlling rootstocks were topped to a height of 2.5m while the Nema Quad systems were topped at 3.5m. Harvest data were collected in the growing seasons 2017-2019. At harvest, fruit count per tree and total weight of fruit was recorded for each data tree. Results were analyzed to identify any significant differences in individual mean fruit weight, fruit produced per hectare, and the relationship between the two. Apart from the C-9 Quad system, yields per hectare and mean fruit size among systems were generally similar with both cultivars, during all three years. Since there were few performance differences among systems, and no consistent differences that occurred two or more years in a row, it appears that orchard systems with size-controlling rootstocks can produce yields on par with the current commercial standard systems. Further trials are necessary to determine long-term viability of these rootstocks and their production capabilities.