There's a promising new angle on mechanical pruning

Issue Date: February 25, 2009

By Bob Johnson

A new method of mechanical pruning may allow growers to slash pruning costs, while providing at least the same yield and fruit quality as is achieved with more conventional hand pruning.

One morning in mid November Erick Nielsen's mechanical pruner rumbled down the row of trees in a Live Oak orchard, making a cut angled down toward the center of the trees.

At the end of the row the machine turned the corner and made a second downward cut from the other side, creating a "V" in the top of the prune trees.

The result of this unusual cut is a more open canopy that allows light to reach fruit near the bottom of the tree next season.

And there is mounting evidence that this "V" cut could be the center piece of a system that will allow growers to slash pruning costs, while providing at least the same yield and fruit quality as more conventional hand pruning.

"In the 1980s when we pruned the trees mechanically we got smaller yields," recalled Bill Krueger, University of California Cooperative Extension tree crop farm advisor in Colusa County. "We just had a flat hedger and couldn't do a 'V' cut like here."

Krueger is working closely with Nielsen to learn how far the more flexible mechanical pruners can go in cutting costs without sacrificing yield or fruit quality.

They discussed the results of their ongoing trial with the growers who came to see a demonstration of the versatile mechanical pruner at Everett Tumber's prune orchard in Live Oak.

So far the results of their experiment look very promising.

In a three-year trial at Nielsen's prune orchard outside Orland, using the machine to make the "V" cut and also hand pruning with a pole saw during the dormant season has slashed total pruning costs by well over half.

"The estimated cost for the hand pruning was $3.25 per tree or $594 per acre with overhead included," Krueger said. "The dormant pole saw pruning is estimated to cost about $200 per acre. The mechanical pruning is estimated to cost about $40 per acre. So, the mechanical plus dormant pole saw pruning would cost about $240 per acre."

This approach has also increased yields by an average of more than 25 percent over the three years. Fruit size and drying ratio have been comparable to the conventionally pruned trees.

These results are only for three years—and the long-term affects of this minimalist pruning remain to be seen. But the results are promising and they may have implications that go far beyond the prune industry.

In addition to growing prunes on his farm outside of Orland Nielsen takes his mechanical pruning operation to tens of thousands of acres throughout the state as Erick Nielsen Enterprises.

His company tops and prunes a wide range of fruit and nut trees including walnuts, almonds, pistachios, oranges and pomegranates, in addition to prunes.

Krueger and Nielsen are looking at finding the combination of mechanical pruning with a supplemental pole saw or a pneumatic saw to get the best yields with the lowest total pruning costs.

In the trial being conducted on a 10-acre block of Nielsen's prune orchard, which is exceptionally productive, they are adjusting the alternatives each year based on what they see.

"All of the treatments get some pruning in addition to the mechanical," Krueger said.

This is a change in approach from two decades ago, when Krueger did trials of mechanical pruning with no hand touch up and found that they reduced yields.

In the current trial different machine pruning cuts are being augmented by different combinations of work with pole saws, pneumatic pruners or lopers and ladders.

Another new wrinkle is that the timing of the mechanical pruning has been shifted.

"We have shifted our mechanical pruning from the dormant season to either mid summer or immediate post harvest," Krueger said.

But the greatest difference could be the equipment that can cut down toward the center of the canopy, creating the unique "V" shape.

"We thought the "V" notch would open up the canopy and get more light to the lower fruit," Krueger said. "It doesn't look as pretty but you get more fruiting area with the mechanical pruning."

In the first year of the trial there were eight different approaches using mechanical and hand pruning to economize over traditional ladder and loper pruning.

All of these eight alternatives produced higher yields, much higher yields, than the more expensive conventional pruning.

That result was not unexpected, as the affect of reduced pruning is generally a short-term increase in yield.

"The first year after you stop detailed pruning you get more fruit; but the question is what happens in the later years," said Franz Niederholzer, University of California Cooperative Extension farm advisor in Sutter and Yuba counties.

But the encouraging news is that some combinations of the machine pruning and pole saw touch up have continued to produce higher yields out to the third year.

The trial will continue in order to learn if this economical approach continues to pay dividends in the longer-term.

But the funny looking trees with the "V" cut may turn out to be a key to reducing labor costs without hurting yields.

"There are some new ways to do it that look promising," Niederholzer said. "The whole point is to see if you could grow good prunes and spend less money pruning."

(Bob Johnson is a reporter in Magalia. He may be contacted at bjohn11135@aol.com.)

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item. Top