Pennsylvania State University horticulturist Dr. James Schupp knows growers face a host of barriers to adopting new technologies. But the rapid adoption of the mechanical string thinner by East Coast fruit growers proves that modern orchard systems can be aligned with new technology to reduce labor costs and improve fruit quality.
Schupp, who is involved in the Comprehensive Automation for Specialty Crops research project that’s looking to increase orchard labor efficiencies, yields, and fruit quality, has searched for new technologies and evaluated existing and prototype ones. His experiences have helped him identify what’s needed for growers to be able to successfully adopt new orchard technology.
Tree architecture is critical, he said. Tree systems must be two-dimensional and columnar in style, with no more than 14 feet between rows. “Twelve feet is better, ten feet best,” he said.
V-style systems can also be mechanized. The concept is to have a continuous wall of fruit to provide a steady workflow as mechanized equipment moves down the row.
Schupp suggested a range of tree densities for these modern orchard systems—between 778 trees per acre for 4 by 14 foot spacings to 1,320 trees per acre for 3 by 11 foot spacings. Single rows of ten-foot tall trees with narrow canopies can accommodate mechanical thinners, pruners, and harvest machines. The canopy will need support with wire and stakes. Size-controlling rootstocks help growers maintain desired tree height.
Schupp said the modern canopy shape complements the natural tree form and lends itself to simplified pruning and training tasks. It also results in good light penetration and light distribution and produces the type of fruit that consumers prefer.
He saw a biaxis system in Italy that he believes has potential because it creates a narrow tree wall of fruit. The biaxis helps split the tree’s vigor into two leaders while reducing the number of trees needed to fill the fruiting wall.
Too many recipes
In addition to high financial investment and high-risk barriers faced by growers, there’s been a lack of standardized systems, he said during the Washington State Horticultural Association’s convention in December. Through the years, orchard training systems have been developed for various reasons, but mechanization was never a driving factor.
“There are more than 30 named apple systems for growers to choose from,” Schupp said. “We have too many recipes out there. Technology cannot be expected to fit 30 different systems. Rather than have 30 systems, we ought to have two or three.”
Preparing for new technology will require change for most growers, Schupp said, suggesting that they consider the tall spindle, vertical V, or inline V as they transition to modern-style orchards.
Field trials of the Darwin blossom string thinner, a mechanical thinner developed in Germany, began in the United States in 2007. U.S. growers have quickly accepted the technology, and some 25 growers in four states have bought machines for both fresh and processed peaches.
“That’s the fastest transfer of technology that I’ve ever seen in my career,” he said.
The blossom string thinner works on angled and vase-style tree canopies, knocking off 35 to 50 percent of the blossoms to prethin the trees. University studies have shown the net economic impact of using the mechanical thinner for processed peaches is a gain of $236 to $1,490 per acre for processed peaches and $185 to $934 per acre for fresh. The increase comes from labor savings and increased fruit size. Mechanically removing blossoms instead of hand thinning green fruit results in larger fruit because the crop load is reduced earlier.
Schupp noted that the string thinner was quickly adopted because tree architecture was already suited to the machine, and growers didn’t have to change existing tree designs. Also, peaches don’t have effective chemical thinning options as do apples, so expensive hand thinning was the only means of adjusting the crop load.
“Limb accessibility was the real key to the string thinner adoption,” he said.
While labor-saving equipment, like orchard platforms and harvest-assist machines, can be expensive, Schupp reminded growers that not all new technology is expensive. He highlighted two inexpensive technologies that are available to better manage crop load.
The Lakso carbon balance model, developed by Cornell University researcher Dr. Alan Lakso, uses ambient light, photosynthesis, and the tree’s carbohydrate supply and demand, to predict the effect of weather on the efficacy of chemical thinners so that growers can make better decisions on when to apply them.
Schupp has also tested a limb-caliper disk developed in France called the Equilifruit disk. The plastic hand tool has notches to measure the diameter of limbs, with a corresponding number on the notch that tells the worker how many fruit to leave on the limb.
In comparing the Equilifruit to a heuristic “rule of thumb” traditionally used by growers, Schupp found that workers using the rule of thumb usually overthinned the tree.
When looking at total yield, the Equilifruit gave favorable fruit size, better overall distribution on the tree, and prevented overthinning, he said, but the disk is only practical on spindle-style trees where renewal pruning is done, Schupp said.
“The point is that there are simple tools now available to increase orchard efficiencies,” he concluded. “They’re not all expensive.