April, 1999
Results from the NC-140 trials and research trials in other countries are beginning to give the Vertical Axe (VA) the nod as the most popular high-density system for apple growers.
I took part in an international symposium on high-density systems for apples in Belgium this past summer. In that meeting, researchers and Extension experts were in agreement, regardless of the location, that the VA system, or its modification, was becoming the most popular system. Growers generally have found it to be a grower-friendly and productive system. Most importantly, it has proven to be a cost-effective system, when considering expenses and returns. More recently, Wolfgang Drahorad, of the South Tirole Advisory Service in northern Italy, repeated these comments in his presentations at the International Dwarf Fruit Tree Association meeting in Hamilton, Ontario, Canada, when he suggested that the 10-foot tall tree was becoming the most popular orchard. Not long ago the apple growing system of choice in that area was the shorter statured Slender Spindle system.
Our data from our NC-140 systems trial at the Clarksville Horticultural Research Station demonstrates the impact of the taller VA tree on yield and labor. In that trial the most efficient and productive combination is Empire and Jonagold on M.9EMLA in the VA at 608 trees per acre. On a per-acre basis, production is equal to or better than trees in the Slender Spindle, but with 400 trees per acre less. For growers, the system of choice (VA) is going to allow no more than 500-700 trees per acre. To make this system perform, we need to have a tree reach 10-12 feet in height.
To reach the 500-700 trees per acre, the plant spacing will need to be around 5 by 14 or 15 feet and grown to a 10- to 12-foot height. Our experience thus far indicates that the rootstock selection makes all the difference in the world to make this system perform. Soil type and geography has a lot of influence on the rootstock selection in Michigan for the VA.
In southern Michigan, which includes the more vigorous soils of The Ridge, Belding/Lowell, southwest and southeast areas of Michigan, we prefer M.9 clones, such as M.9 RN 29, Pajam 2 and M.9 EMLA for the taller canopied VA systems.
Trees on M.26 (especially for Empire) and G.30, although large, also have a place for VA in southern Michigan. Even though we have relatively little experience with G.30 in Michigan, it appears to have promising potential for growers because of its vigor, productivity (similar to M.9) and its tolerance to fireblight. Note that the supply of this stock is limited because it is relatively new and there appear to be some serious propagation problems in the nursery.
The other M.9 clones such as M.9 NAKB 337, Pajam 1, and the non-M.9 clones like Bud.9 and Mark are also very productive. However, these clones are much weaker and don’t belong in the taller VA systems. Instead, these stocks work well for the shorter-statured Slender Spindle and V systems in tight spacings. Additionally, the more vigorous M.9 clones offer more flexibility to the grower and have more tolerance to error. While irrigation is still recommended, they at least have more vigor to get past droughty conditions better than the stocks with the weaker root systems. Secondly, these taller trees are less vulnerable when it comes to spring frost by producing more flowers and fruit higher in elevation compared to the shorter systems.
For orchards in northern Michigan, the soils are generally sandy, droughty, infertile and the growing season shorter. As a result, the traditional dwarfing M.9 clonal stocks rarely fit unless the grower has a fertile site and applies plenty of water.
Mark, Bud.9, NAKB 337, Pajam 1 and other weaker growing M.9 type clonals don’t belong in most northern sites, unless they are planted in a Super Slender Spindle system at one to two feet apart.
If an M.9 clone is still the desirable choice, then I recommend using clones that possess some vigor. In this case, the most vigorous M.9 clones, such as M.9 RN 29, Pajam 2 (Cepiland) and M.9 EMLA work best. Realize that these stocks are less cold hardy than Bud.9, M.26 and likely G.30. Under most site conditions in northern Michigan these stocks should be planted at spacings of a maximum of 4 by 13 or 14 feet.
Secondly, don’t have tree height expectations beyond eight feet for these trees, even with keeping the leader fixed erect to a stake as in the VA. Should the grower prefer the taller tree of 10-12 feet, then follow the same training protocol (VA) using M.26 or G.30 (M.7 at wider spacings of seven to eight feet). In most northern Michigan sites, G.30, which is twice as productive and precocious as M.26 and equivalent to M.9, can be treated as M.9 clones in more southern areas of Michigan if planted with a support system, at 5-6 feet by 14-15 feet.
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