WA 38 rootstocks and training systems

WA38-1 WA38-2
WA38-1 WA38-2


The WA38 apple project will provide useful information about the management of Cosmic Crisp™ (WA 38) before the variety is released in 2017:
1. Identify growth and productivity characteristics of WA 38 on Nic 29 and Geneva 41 trained to conventional vertical and angled systems.
2. Identify growth and productivity characteristics of WA 38 on Nic 29 and Geneva 41 trained to a bi-axis (fruiting wall) with and without mechanization.
3. Conduct an economic analysis of WA 38 production in the three training system scenarios.

The WA 38 tree has been characterized by an upright and spreading growth habit with medium vigor (like Granny Smith is a Type IV). It is precocious, with spur development on two-year-old wood and the tendency to produce in the outer part of the canopy and leave blind wood near the trunk. The fruit is crisp, firm and juicy with non-browning flesh and consistently showing excellent long term storability (Evans et al., 2012). Preliminary information on its behavior on different rootstocks and training systems has been provided by the Phase 3 evaluation of the breeding program. It is now time to evaluate WA 38 in a multi training systems trial located in two different sites: WSU Wenatchee Sunrise Orchard and WSU Prosser Roza Orchard.
The two-site trial mentioned above was planted in 2013 to assess the variety utilizing trees from the nursery grafted on two rootstocks, M9 (Nic29) and Geneva 41. Two training systems, spindle and V-system, are compared in this trial with densities of 1,499 trees/acre and 2,997 trees/acre, respectively (Fig. 1). Nic29 is the most vigorous and strongest among M9 clones and Geneva 41 is more dwarfing, winter hardy, very precocious, fire blight resistant, replant tolerant and woolly aphid resistant.
In the same planting, one-year-old trees were headed back at 2 ft to develop a bi-axis tree (Fig. 2) that will be one year younger than the spindle and V-system trees. Half of these trees will be trained to a fruiting wall and all tasks will be carried out with varying degrees of mechanization. The studies on mechanization will be carried out only on the fruit wall system because is more suitable for an early management. The cost of tasks will be tracked in this block to allow for an economic comparison between cost of production with labor assist/mechanization and with traditional (non-mechanized) production. This study will identify any unique barriers to mechanization that might exist with WA 38 and/or the training system.

PI: Stefano Musacchi

Co-PI: Matt Whiting, Karen Lewis, Karina Gallardo, and Tom Auvil

Collaborators: Sara Serra

Start date: 2014  |  End date: 2016

Source of funding: Washington Tree Fruit Research Commission (WTFRC)