Mar 17, 2020
Precision key to ideal crop load management

Terence Robinson, a tree fruit physiologist with Cornell University, has been an influencer in the evolution of apple training systems for 35 years.

He maintained that posture when he took the podium during the International Fruit Tree Association’s 63rd Annual Conference and tours held Feb. 9-12 in Grand Rapids, Michigan.

Robinson maintains that if apple trees fail to fill their space after three years, there is a ‘huge economic penalty” in lost yield and income.

“Matching rootstock vigor with scion vigor, soil vigor and climate vigor that gives the best combination of growth and yield for the variety is a key management decision,” Robinson said.

“Growing a small tree, that’s got to grow a lot of canopy to get that space filled, it’s taken me two to three years. I think that’s not the right way to go. Planting more trees, planting and having an ‘instant orchard’ is the more profitable way to go because you get the payback in investment much quicker.”

Robinson favors planting grow-through trees on a two-year cycle. In the first year, the strategy is to bench graft in late winter and then grow a grafted tree to four feet in the first year using raised beds and black plastic mulch. Year two will include growing an eight-foot tall tree with 15-20 short feathers. In year three, growers should plant an “instant orchard” that can produce 300-400 bushels an acre in the second year.

“Plant new orchards only with high priced varieties, and grow trees 10-12 feet tall,” he said.

“We have to design orchards for high light interception but also high conversion efficiency.”

“It turns out that our analysis still shows the optimum economic density is still somewhere around 1,300 trees per acre – 2,300 a hectare – but you have to grow them tall.”

A 1:1 ratio of tree height to row width gives the optimum light interception. Trees taller than row width lose fruit quality. There is a yield penalty if a pedestrian orchard (seven-foot trees) does not reduce row width, also.

“My problem in the East, when you start with little trees that are 4-foot tall, it takes us three to four years to get them up to nine to 9-feet tall. To get to 12 feet, it takes you forever. You have to do something different.”

Robinson often finds “it’s so depressed when I go out to an orchard. They’re four years old, and we can’t get the tree to the top wire. We’re losing a ton of money when that happens to us. Some of you say ‘I’m from a north climate, I can’t do nothing.’ You can’t accept that. You have to figure out a way to maximum rootstock vigor. In rootstocks, we have a range of vigor now that are fairly efficient. You have to pick one that’s going to push the tree enough. Maybe you have to switch to grow-through trees and center plant into the orchard.

Bi-axis option?

In considering the value of a bi-axis tree, Robison said if vigor is excessive, then having two leaders results in less vigor of each leader.

Most orchards in the northern producing regions lack vigor and thus bi-axis is only a modest improvement, not a “game changer,” he said.

“My point is select a rootstock that has high conversion efficiency, but will fill the space in two to three years and will be easy to manage at maturity in old age.”

“Some of the shapes, the V-shapes, do have a problem in the lower part of the canopy. Reflective film has been marvelous in overcoming that disadvantage,” Robinson said.

There are lesser benefits from biaxis trees if planted at the optimum density of 1,300 trees per acre, but if planted at lower density there is an early yield penalty.

“There are some benefits to bi-axis or multi-axis trees,” Robinson said. “But there are also less advantages. And unless I’m proven wrong, I don’t believe those are game changers. What is a game changer, is getting high yield over the first five years and recouping the entire investment by the end of the fifth year.”

Robinson said is a penalty for trying to grow a two-dimensional canopy versus a three-dimensional canopy unless growers go down to narrow rows of seven or eight feet.

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Robinson acknowledged fruit color and quality are better at any given tree height with between row spacing with a two-dimensional versus three-dimensional canopy. However, there is a yield penalty for a narrow two-dimensional canopy compared to a three-dimensional canopy at any tree height. It’s also necessary to invest in technology that improves fruit quality (sunburn and color).

“Is 100 bins an acre of 80% packout worth more than 80 bins of 95% packout? It becomes an economic question.”

Robinson said it does make sense to grow a bi-axis or cordon tree and plant to density, but there are trade-offs. Early light interception is tied very tightly to tree planting density. If a grower plants fewer trees per acre with a bi-axis, they will have lower early light interception and thus lower early yield.

“Yield drives profitability and thus the savings in tree cost results in lost yield and reduced profitability. There is an optimum tree density for optimum profitability. Any lesser density results in less profit.”

“The idea that we’re going to go twodimensional for robotic pickers on our 11 to 12-foot rows just because that’s what the engineers demand, there will be a penalty. Maybe it’s still going to be profitable, but we still have to understand that penalty.”

Robinson also believes there is a very substantial cost in planting small trees from on-farm nurseries.

“However, I have argued against it for 35 years, but I came back from my sabbatical leave, and I said, why argue with them, let’s join them. I’m in favor of it if you can do a grow-through tree and plant an eight-foot-tall tree.”

— Gary Pullano, managing editor