Pros and Cons of Mechanical Pruning

Luke Milliron, UCCE Orchard Systems Farm Advisor, Butte, Tehama, and Glenn Counties; Franz Niederholzer, UCCE Orchard Systems Farm Advisor, Colusa, Sutter, and Yuba Counties

Some prune growers are adopting mechanical pruning as an alternative to standard hand pruning of mature, bearing trees as labor costs climb and labor availability drops.

The cumulative result of this style of mechanical pruning is unclear and should be studied. However, some generalized pros and cons can be gleaned from UC research and grower experience.

Definitions for this discussion:
Mechanical pruning: a ‘boxed’ treatment applied every year, consisting of mechanical topping plus two-way hedging during post-harvest. Includes some hand cuts for removing suckers, diseased and dead wood.
Hand pruning: selective cuts made annually with loppers and the assistance of ladders. Includes a mechanical topping every other year to reduce labor costs.

Pros of Mechanical Pruning:

  • Cost: Some growers report that standard hand pruning can cost approximately $1000 per acre, while a mechanical hedging and topping program may be closer to $250 per acre.
  • Availability: We are hearing reports that pruning crews are not available in some areas at any price, and if they do start an orchard, may not stay to finish the job.
  • Total Value: A 2006 to 2009 UC study evaluated various timings (June, September or dormant) for mechanical pruning treatments (flat topping, angled canopy “V” or “mohawk” cuts, etc.; treatments included large thinning cuts and no hedging). In this trial, the standard hand pruning treatment had lowest cumulative economic value compared to a range of topping cuts, indicating potential for economic gains from moving to a program that includes at least some mechanical pruning. The annual report for this study (CPB 5) and others on pruning research are available at the  Read the annual report from this project (CPB 5) and other research on pruning at the Dried Plum Research Report Database

Cons of Mechanical Pruning of Mature* Orchards:

  • Disease risk: Hedging results in thousands of indiscriminate cuts that are potential entry points for rain-splashed fungal spore infection from diseases such as Cytospora and Botryosphaeria (figure 1). Spraying with a fungicide protectant like Topsin-M® soon after any pruning can reduce the risk of infection.  
A 15-year-old orchard that has been mechanically ‘boxed’ for seven years showing branch dieback (tree on the right). The orchard manager had not previously protected pruning wounds with a fungicide but plans to start this year.

Figure 1. A 15-year-old orchard that has been mechanically ‘boxed’ for seven years showing branch dieback (tree on the right). The orchard manager had not previously protected pruning wounds with a fungicide but plans to start this year.

  • Reduced fruitwood thinning: Mechanical hedging doesn’t selectively thin fruitwood to improve fruit size. Instead, shaker thinning, as needed, is relied on to achieve good fruit size. Reduced fruitwood thinning may also result in fruit on positions that are more difficult to shake such as long “hanger” spurs. If a grower is going to stop detail pruning in an orchard, estimating fruit per tree and shaker thinning –where needed– will be essential to avoid growing a big crop of small, low value fruit.
  • Unknown long-term results: This ‘boxed’ style of mechanical pruning has not been evaluated by UC researchers. Despite anecdotal grower success, long-term results on yield, dieback and overall orchard longevity are unknown.

Differences in equipment, orchard design and grower preference make for many ways to “mechanically prune”. Be aware of the challenges and potential benefits of shifting away from ladders and loppers as labor becomes more expensive and less available. We encourage you to talk with neighbors, industry reps, PCA/CCAs and your local UC farm advisors when developing a pruning program this fall.

*We are unaware of any growers who have eliminated hand pruning of young trees. Careful hand pruning is still needed to develop trees that will carry good to heavy crops year after year for the life of the orchard.

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