for Mechanical Pruning
Demonstrations
- By Karen Gentry
Associate Editor
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More than 50 Michigan growers gathered in Lawton, Mich. in December for demonstrations of two hedgers and two cane positioners in a vineyard operated by Mark Gregory of Gregory Farms. The demonstrations were led by Tom Zabadal, from the Southwest Michigan Research and Extension Center, who helped develop a prototype for mechanical pruning in the early 1990s.
Pruning requires more labor than any other task in the annual cycle of vineyard management, according to Zabadal. In the past mechanical pruning resulted in long-term decline of vine size and productivity. Zabadal said in recent years technological innovations have made mechanical pruning a viable, cost-effective alternative to manual pruning, although it can hurt the vines if not done properly.
Gregory has been mechanically pruning his grapevines since 1996 on 65 acres of Concord grapes. He waited as Zabadal, and Gary VanEe, professor of ag engineering for Michigan State University (MSU) developed a prototype of equipment that he felt he could use for pruning grapevines before purchasing a hedger in 1996.
“I’ve been able to maintain the same quality of fruit and the same tonnage. Being a small operator, I try to do as much as I can myself,” said Gregory about mechanical pruning. Once a year in the winter he begins his pruning process.
First he runs a cane positioner through his vineyards to make canes that tend to grow horizontally more vertical. “The hedger is able to cut more off that way. The idea is to leave 70-90 buds per vine. I couldn’t accomplish getting enough off unless you comb them out,” Gregory said.
Gregory uses a tractor fitted with an arm that raises up and down. He attaches the cane positioner to the arm of the tractor for the first step in pruning the vines, a procedure that takes about two hours per acre. Gregory takes the positioner off and mounts the hedger on the same attachment using the same tractor. Hedging takes about 1 1/2 hours for an acre.
He does a walk-through of the vineyard between mechanical operations to replace the cordon and to make cuts in some remaining brush the positioner wouldn’t pull down. He also replaces vines during the walk-through which generally takes 1 1/2 hours per acre.
Mechanical pruning saves Gregory one to 17 cents per vine and three–five cents per vine for tying that normally goes to workers. He estimates there are 500-600 vines per acre. In the past he paid out $4,000-$5,000 to three–four workers for most of a month plus his additional time spent hand pruning.
Gregory uses a hedger manufactured by Gillison’s Equipment Company in Benzonia, Mich. “I just bought the cutter, not the whole unit,” he said. He adapted the cutter to his own tractor. Gregory said it would cost growers a lot more if they aren’t able to do the hydraulics and welding to adapt to their operations. Gillison’s will soon introduce a commercial version of cane positioner as an attachment to their hedging equipment.
“I think this is going to catch on and be the wave of the future,” said Gregory. He said the cane positioner has helped to be able to do a more complete job.
“It’s a tribute to Dr. Zabadal and engineers there (MSU). We all appreciate their efforts,” Gregory said.
“We’re the only ones advocating cane positioning,” said Zabadal. He said cane positioners are used in the dormant phase for cane positioning and in the growing season for shoot positioning.
Pruning Concord grapevines
Zabadal and other MSU researchers evaluated several strategies for mechanical pruning of Concord grapevines in a six-year experiment at the Grabemeyer Farm in Sister Lakes, Mich. Zabadal found that severe mechanical pruning that attempts to simulate hand pruning practices with the removal of 80-90% of mature buds on a vine during the dormant season provided results comparable to commercial hand pruning in yield and fruit maturity.
The first mechanical pruning unit was fabricated by MSU in 1992 featuring a dual-action cutter bar and rotating tines at the base of the cutter bar.
A unique gearbox, modeled after a design that was developed and manufactured by Gillison’s for larger pieces of equipment, was used with a vertically oriented cutter bar so that there are moveable teeth on both blades.
Cane positioning
Numerous mechanical pruning units often retained too many fruiting nodes so vines developed too large a crop with unacceptable fruit quality. Efforts were made to reduce the follow-up hand pruning needed for the desired level of pruning severity.
Many of the excess, undesirable nodes retained on Corncord vines after hedging are situated on canes running on top of the trellis. Researchers reasoned that if those canes could be moved out away from the cordons on top of the trellis, then they would be better targets for the hedging operation. After numerous efforts, a cane positioning head with a proper design, tine orientation and durability was field tested in 1998 and has performed well under a variety of conditions, according to Zabadal.
The cane positioner can also be used as a shoot positioning device to enhance fruit exposure and overall fruit quality. Research showed that mechanical shoot positioning two weeks after bloom significantly increased fruit soluble solids accumulation by an average of 0.4 brix for the research period with no influence on yield.
Preparing a vineyard
Most of the trials in this project involved vines trained to the Hudson River Umbrella (top-wire cordon). Successful mechanical pruning requires vines to be trained in a stable, well-engineered trellis. Vines with sagging cordons and crooked trunks are poor candidates as are trellises with loose wires.
Medium-to-large size vines are best suited for mechanical pruning because they’ re capable of tolerating the less precise pruning severity achieved through mechanization than with hand-pruning. To sustain mechanical pruning, growers need to continue stimulating vine size through weed control, fertilization and pest management.
Because the mechanical pruning described is non-selective for the nodes retained on the vine, it is necessary to retain more nodes on mechanically-pruned vines than for those hand-pruned to achieve the same fruiting potential.
Mechanical pruning strategy
1. Shoot positioning – Performed two weeks after bloom. Enhances development of fruit soluble solids in most years and starts the process of reorienting shoots so canes will be better targets for mechanical pruning.
2. Cane positioning – Completes the reorientation of most of the canes that can establish themselves at the top of a trellis.
3. Cordon renewal, trunk renewal and managing unpositioned canes - Mechanical pruning may eliminate canes that are needed for cordon renewal or trunk renewal. Perform these tasks prior to mechanical pruning. Portions of loosened cordons from the top wire should be reattached prior to the hedging operation.
4. Mechanical pruning – Performed at a ground speed of approximately one mile per hour, this takes about two hours per acre. Grower refinements include: a) the pitch of the cutter blade relative to the plane of the trellis so that it becomes more or less aggressive as it is tilted toward the trellis; b) using a foot pedal to instantly stop or reverse cutter action; c) the angle of the cutter blade from vertical so that the top portion of the cutter is angled out away from the trellis, canes are pruned less severely at the top and left longer than if the cutter bar was positioned vertically.
5. Followup - Walk the rows to remove any portions of vines that have obviously been missed.
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