March, 1999
By Ron Perry and Gail Byler
Michigan State University
Intensive orchard management systems utilizing dwarfing rootstocks have now become commonplace as a standard practice in North America for apple production.
Some of the questions regarding what are the best rootstocks and orchard systems have been categorically answered related to horticultural parameters. It has become increasingly apparent through reports on intensive orchard system experiments that in the first seven years of an orchard planting, plant density is the one critical factor in productivity, even more important than system design or other factors.
One system that achieves the goal of accelerated planting density without inhibiting canopy light penetration is the "V" system. The Guttingen V system was developed at the Guttingen Research Station in Switzerland. Commercial growers in Europe and in the U.S. have begun to adopt the system and, in some cases, have modified it for their conditions. One major modification is making the system an all-wire support system (similar to the Taturra), rather than the individually staked supported trees developed originally in Switzerland. A trial was established in 1993 with Imperial Gala planted on 19 rootstocks on the Guttingen V and V-trellis system. This planting has been productive since it first started producing significant crops in the fourth growing season.
Three hundred and twenty trees with Gala scion were established in a split plot randomized complete block design in 1993 at the Clarksville Horticultural Experiment Station. The main plots of the experiment are two V systems - Guttingen V and the wired V trellis. All trees were supplied with trickle irrigation soon after establishment and planted at a spacing of 2.5 x 13 ft. or a density of 1,340 trees per acre. The Guttingen V trees are supported by a two-wire system with metal tubes and an angle of approximately 20° from vertical. The trees on the wired V have no tube support and instead have eight wires (four on each side). Support in both systems extends to a height of seven feet. The trees have been trained since establishment in the slender spindle fashion, with trees leaned to 20° from vertical, each in an alternate direction down the row.
The sub plots within the system tested and compared the performance of 19 rootstocks. Rootstock treatments include: Mark, Bud.9, M.9, M.9 EMLA, Vineland 605-1, Vineland 605-3, P.2, P.22, M.9 NAKB 337, M.9 NAKB 338, M.9 NAKB 339*, M.9 NAKB 340, M.9 Janssen NAKB 337, RN 29, MAC 39, CG 10, Burgmer 751, Burgmer 756, and Burgmer 984.
Since establishment we have been collecting data on tree vigor (measured by trunk caliper), yield and average fruit size.
Results and discussion
A statistical analysis performed on the yield data does not indicate that there is a significant difference (statistically and economical returns) between the trees planted and trained in the two systems. So from a grower’s perspective, the system support of choice is entirely up to the orchard operation, personal preference and resources.
The wired-V system can be a little less costly, because of the comparison in expense of purchasing metal supports versus wire on a per-acre basis. We noticed better branching, horticulturally, in the wired-V trellis system. The tradeoff is that it is a little more inconvenient to harvest in the trellis system.
The rootstock influence on vigor, cropping and fruit size is interesting (Table 1 and Chart 1). There appears to be little difference, statistically, between the top 12 rootstocks for cropping.
Topping the list is Mark followed by Burgmer 984 (M.9 clone from Germany), M.9 NAKB 339 (sister clone of 337), and NAKB 340. The bottom four rootstocks in cumulative yield since 1993 include V.1, P.22, CG.10 and Mac 39. Note that in the first five years of cumulative yield, none of the treatments approached the goal of 2,500 bushels per acre that Terence Robinson, Cornell University has challenged high-density growers with.
Considering the fact that there are 1,340 trees planted per acre, that is a disappointing statistic. This goal may not be as reachable with this variety as it is with others. In our 1990 NC-140 systems trial, Gala used as guard trees in the trial on the best rootstocks (Bud.9, Mark, M.9 EMLA and Ottawa 3) barely reached 2,000 bushels an acre at the end of five years. The difference, however, is that the trees in the systems trial were planted at a much lower plant density of 608 trees per acre and trained to a much cheaper Slender Cone (HYTEC) system. In both these trials Gala cropping in the second and third years was relatively low in comparison to other varieties. In the systems trial, Jonagold and Empire five-year cumulative yields surpassed 2,500 bushels an acre in both the slender spindle and vertical axe at 996 and 608 trees an acre, respectively.
If we evaluate rootstock performance with the small-fruited Gala, it is important to review production and fruit size in the same view. Chart 1 shows that the more impressive rootstocks in 1998 were those which had high cropping and maintained relatively good fruit size. Those stocks included Bud.9, NAKB 340, and Bg.984. This is not the first time that we have found Bud. 9 to both produce good yields and good size fruit with Gala. We had the same experience in the 1990 systems trial, where Bud.9 was best for both yield and fruit size among eight stocks, which included M.9 and M.26 in the test.
Conclusions
It is still too early to make too many conclusions in this six-year-old planting regarding rootstocks. We only have leading candidates for the closely planted V.
Because of the tight spacing, Bud.9 is probably the rootstock best suited, when you take in all considerations, such as vigor (120% of NAKB 337), yield, fruit size, innate cold hardiness and resistance to phytophthera.
In other trials, the normal comparative vigor of Bud.9 to NAKB 337 is that Bud.9 is the same size or 5% smaller. The jury is still out on V orchard system for Midwestern apple growers from the monetary perspective. Remember that the initial capital outlay is high. At 1,340 trees per acre, and an estimated $5 per-tree cost, that equates to $6,700 per acre, not counting trellis support estimated at another $2,500-$3,000 per acre. It would mean that you would have to have a more precocious variety (high, early-bearing yields) that commands a high per-unit price to pay for the system.
I’m not suggesting that it can’t be done, but the challenge is there, especially with Gala. There are always ways to overcome these obstacles, which separates the resourceful growers from others; for example, if the grower produced their own trees or if they were able to reduce costs on support materials. Secondly, the V still has great potential for adoption by PYO or direct-sale operations, where fruit prices can be more lucrative and where land space is limited.
These trees have been extremely impressive at the Clarksville Horticultural Experiment Station and we look forward to the potential of higher cropping in the future. We hope to continue the trial with the supplemental support granted by the Michigan Apple Research Committee.
Ron Perry is with the Department of Horticulture at Michigan State University and Gail Byler works at the Clarksville Horticultural Experiment Station.
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