Evaluating Training Systems In Establishing Precision Orchards

Greg Lang

Greg Lang

The NC-140 Sweet Cherry Canopy Architecture and Rootstock Trial has been (and continues to be) a valuable experiment for guiding the development of greater precision in cherry orchard management. This trial was planted in 2010 at 13 sites across North America, though it remains only in Michigan (with ‘Benton’), New York (two sites, with ‘Regina’), and British Columbia and Nova Scotia (with ‘Skeena’) due to disease, deer damage, or scientist retirements across the other sites.

The rootstocks in the trial range from dwarfing (Gisela 3, Gi3) and semi-dwarfing (Gi5) to semi-vigorous (Gi6), and the canopy architectures include Tall Spindle Axe (TSA), Kym Green Bush (KGB), Upright Fruiting Offshoots (UFO), and in Michigan and New York, Super Slender Axe (SSA).

Advertisement

In Michigan, the NC-140 trial site at Michigan State University’s Clarksville Research Center is on a very fertile soil, resulting in the most vigorous growth of any of the current sites.

Since the trial was planted at uniform tree spacings (5 feet, except for the SSA at 2.5 feet), one goal was to examine how well each architecture/rootstock combination filled the allotted orchard space at the end of Year 3 (2012), and develop appropriate tree and row spacing recommendations for sites with soils and climates likely to promote similar tree vigor.

Top Articles
Have a Plan For Climate Change? Why Fruit Growers Need To Act Now

This resulted in tree architecture/rootstock combinations that range from 515 to 1,936 trees per acre (Table 1). Consequently, this comprises the first factor in orchard establishment costs. If average nursery tree cost is $10, the baseline orchard tree cost would range from a little more than $5,000 per acre (KGB/Gi6) to just under $20,000 per acre (SSA/Gi3). Not surprisingly, those extremes also reflect the lowest (KGB/Gi6) to highest (SSA/Gi3) early yield potentials.

Costs Associated With Training Systems
Another differential economic factor for establishment of these sweet cherry training systems is trellising. The KGB and TSA are freestanding canopy architectures. The SSA can be freestanding, but posts and top wires (and perhaps a temporary lower wire) are advantageous for tree alignment during establishment, since the goal is a narrow, uniform fruiting wall suitable for potential adoption of mechanized platforms for pruning, harvest, and/or hedging. Similarly, the UFO requires a bottom wire for horizontal training of the “cordon” leader, plus either several additional trellis wires or a top wire with twine tied about every 8 inches to the bottom wire for orientation of the multiple vertical fruiting leaders to create a narrow, uniform fruiting wall.

Such trellis materials add significantly to orchard establishment costs, though if the orchard is in a location where bird netting or rain covers are needed, the use of posts might already be part of the overall orchard infrastructure cost. Certainly, irrigation is an additional establishment cost across all canopy architectures, though tree density can affect the number of irrigation lines per acre.

NC-140 Cherry Rootstock TrialYields A Big Factor
Thus, with general orchard establishment costs and early yield precocity, key remaining economic factors for these intensive orchards include mature yields and labor efficiency for annual pruning and harvest. Yields thus far have been quite variable due to the many risks inherent with sweet cherry production. The first significant crop (2012) was lost entirely due to a record early bloom followed by multiple frost events. This not only killed young fruit, but also caused bacterial canker infections that killed spur and shoot meristems, thereby impacting future yields in 2013 and 2014 as well. Poor pollination conditions in spring 2014 and 2015 had additional negative impacts on yields, with June drop in 2015 approaching 80% on some trees.

Consequently, preliminary data for cumulative yields projected on an orchard basis (using the recommended spacing in Table 1) from 2013 to 2015 (Years 4 to 6 after planting) have been highest for the TSA/Gi3 trees at 16.3 ton/acre, followed by the UFO/Gi3 at 13.7 ton/acre. The most productive trees through Year 4 (2013) were SSA/Gi3, but subsequent yields in 2014-15 have not kept up with the increasing yields of the TSA, UFO, and KGB trees. Cumulative yields for SSA/Gi3 have been 9.4 ton/acre, only slightly higher than UFO/Gi5 at 8.7 and TSA/Gi5 at 8.5 ton/acre.

The lowest cumulative yields have been on SSA/Gi6 and KGB/Gi6 at 2.4 and 2.6 ton/acre, respectively. At Clarksville, the strong vigor of Gi6 is excessive for the ultrahigh density SSA canopy architecture, creating fewer flower buds and more shade.

The low yields of the KGB likely could have been improved if a greater number of vertical fruiting leaders had been created during canopy structural development, thereby moderating annual growth to promote more spur development. This illustrates how training systems such as the KGB and UFO, which utilize development of a variable structure of multiple vertical fruiting leaders, can be managed for greater precision in cropping after planting. If annual vigor of the upright leaders is too great, the number of leaders can be increased to moderate growth potential and promote spur formation across more fruiting units. If annual leader vigor is too weak, the number of leaders can be reduced to invigorate the remaining fruiting units, increasing leaf area and moderating flower bud formation.

Such simplified fruiting units make it easier to estimate leaf area and flower bud balance to achieve a more precise crop load (leaf-to-fruit ratios) of specific quality fruit. Analysis of the data thus far from each of the NC-140 trials is currently being undertaken, with analysis and conclusions across sites expected later in 2016.

Stay tuned!

0