Good Fruit Grower / April-15th 2012 / Get spacing and ­rootstock right

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Get spacing and ­rootstock right

Growers making the best choices make the most money.

Choosing the right apple varieties—ones that enjoy good consumer demand and sell for a good price—is the most important step an apple grower can take toward profitability, says Dr. ­Terence Robinson, Cornell University pomologist.    

But once a grower makes his choices, the real hard work begins. The orchard needs to be planted, and the choice of rootstocks and spacings are vitally important.

“If you do everything right, you can still make money if you plant the right variety in an 8 by 16 spacing and 340 trees per acre,” Robinson told apple growers at the Mid-Atlantic Fruit and Vegetable Convention in ­Hershey, Pennsylvania, in February.

But, he added, economic analyses show the highest profitability occurs when growers plant about 1,000 trees per acre. It is up to the grower to find the combination of rootstock and soil that will fill the space rapidly but not be too vigorous at that spacing.

In making decisions about rootstocks, growers must look at economics (precocity and productivity), liveability, rootstock vigor, scion vigor, climate, soil type and fertility, irrigation/fertigation, replant disease, ­spacing, and training system, he said.

Robinson is one of the developers of the tall spindle system, in which trees are trained to grow 10 to 12 feet tall in a narrow profile that contains no permanent scaffold limbs. Using that system, a thousand trees planted three to four feet apart in rows 10 to 12 feet apart will fill an acre.

He suggests the following:

—Use a 3-foot spacing for weak and medium vigor varieties.
—Use a 4-foot spacing for vigorous varieties.

From strongest to weakest, he ranks scion vigor in this order: Mutsu, Northern Spy, Jonagold, McIntosh, Cameo, Fuji, Gala, Empire, Idared, Greening, Macoun, ­SweeTango, Jazz, Spur Delicious, NY1, and Honeycrisp.

Geneva rootstocks

Cornell has had a rootstock breeding program for some time, and its Geneva rootstocks are just now reaching commercial availability. Robinson is convinced they will be superior because they were selected to be disease resistant, precocious, and productive. But there are not enough of them now.

In making rootstock decisions to get the right ­rootstock to fit the spacing, he suggests:
—Use vigorous clones of M.9 (Nic29 or RN29) for medium vigor cultivars or when planting on replant soil.
—Use weak clones of M.9 (T337 or Flueren56) for ­vigorous varieties or on virgin soil.
—Use M.26, interstems, or M.7 for very weak varieties.
—Use irrigation and/or fertigation to improve lack
of vigor.
—Use limb bending and limb renewal pruning on tall spindle system trees to keep trees slender.

Rootstocks that live

In choosing a rootstock, the primary consideration is, will the tree live, he said.

“Fireblight is devastating in New York and in Michigan and some other areas,” he said. “Some method to control fireblight is critical.” Fireblight infects blossoms and can move, in 60 days, down into the rootstock. “If M.9 and M.26 rootstocks become infected, the tree will die,” he said.

“Geneva rootstocks are resistant to fireblight,” he said. “If the rootstock doesn’t die, we can quickly regrow the parts of the tree that are lost in a fireblight epidemic and not lose the orchard.”

Cornell has been working to breed and prove new rootstocks for several years, with the specific goal of putting fireblight-resistant rootstocks and/or replant ­disease-resistant rootstocks into each of the current size niches from small trees to large.

So far, not many Geneva rootstocks have been available for growers to plant. About 325,000 were produced in 2009, 400,000 in 2010, and 600,000 in 2011—in a market that needs 15 million rootstocks a year, he said.

“There will be 500,000 G.11 liners planted in U.S. nurseries this coming spring and 1 million in 2013,” he said. Production of G.41 this year will be nearly 300,000, he said.

Geneva released seven rootstocks before 2010, and another six since then. Of the rootstocks now being commercialized, G.65 is the smallest (M.27 size), G.11 is the size of M.9 T337, G.935 is the size of M.9 Pajam2, and G.41 and G.16 are in between G.11 and G.935. G.202 is the size of M.26 and G.30 the size of M.7 and MM106.

The releases made in 2010 are G.214, just larger than M.9 Pajam2; G.222, just smaller than M.26; G.969 and G.213, just bigger than M.26; G.210, the size of M.7-MM106; and G.809, which is halfway between M.7 and seedling size.

Growers should look closely at the NC-140 rootstock trials to see which rootstocks perform best in their area. This is critical, he said.

He noted that, at Champlain, New York, the northerly production area just south of Montreal, varieties on M.9 rootstocks yield only 67 percent as much as the same varieties and rootstocks planted at Geneva, where winter temperatures are warmer, he said.

Yet when planted on G.935, they do equally well in both places. G.935 is a cold-hardy rootstock, he said.

G.214, which is the size of M.9 Pajam2 and rated as highly yield efficient, productive, resistant to fireblight, and tolerant to replant disease, has not as yet produced any liners for commercial use.

“We have had a setback in the development of stool beds of G.214, and its propagation is starting over, an 18-month delay,” Robinson told growers in January during the International Fruit Tree Association tour to Chile. That news was ­published in the January 15 Good Fruit Grower magazine.

Density effect

Robinson also said that growers must learn from experience how to compensate for the density effect when choosing ­rootstocks. While the rootstock itself affects the size of a tree, and thus ­determines how closely they can be spaced, the spacing affects root competition, so closer spacing itself produces smaller trees.

Management of the tree also affects its size. When limbs point upward, the tree will grow shorter and wider, he said. If the feathers are bent down below horizontal, trees will be taller and slenderer.

Large means large

“Large branches create large trees,” he said. Smaller branches are taxed more heavily to support fruit than are large branches. Consequently, large branches transport more carbohydrate back to the trunk, and the tree will become still larger.