INTRODUCTION

When and how olives are harvested are among the most important factors in both the quantity and quality, and therefore value of processed table olives and olive oil. Efficiency of harvest, the percent of fruit removed from the total crop on the tree, is the first component of total processed product value. Quality of the fruit, partially a function of maturity for table olives and oil, and size for table olives, and condition when delivered to the processing facility is the second component of total processed oil or table value. Harvesting is the final step in field production of an olive crop, but if done at the wrong time or in the wrong way it can markedly affect net return to the grower. However, within limits, depending upon the use of the harvested fruit, the two factors are ranked differently.

Efficiency of harvest removal and collection is the more important factor in developing mechanical harvesting for olives destined for olive oil.  Fruit quality and condition, within limits, is secondary. Fruit quality and condition, the potential for producing an acceptable table fruit when delivered to the processing plant, is the most important factor in developing mechanical harvesting in olives destined for table fruit. Efficiency of harvest is secondary. Given the relative size of the world’s olive oil and table olive industries, and the relative difficulty of developing mechanical harvesting for oil or table fruit, successful harvesting of olives for oil is being developed sooner and more easily than successful harvesting of olives for table fruit processing.

The major reason for developing mechanical olive harvesting is the high cost of hand harvesting; currently the single most expensive cost in olive production worldwide. In California’s San JoaquinValley the 2009 average hand harvest cost per ton was approximately 50% of the gross return per ton. Other major olive producing countries report similar percentages. Further, in most olive producing countries adequate supplies of harvest labor are less available, and the liability to meet  safe working and fair employment standards is becoming more difficult.

These two factors, the potential for olive harvesting methods to affect the quantity and quality of the final processed product, and harvest costs, mean efforts to develop mechanical harvesting for olives must be dictated by both the quality of the table olives or oil produced and by the reduction in harvest costs. Though, as discussed above these factors, within limits, rank differently depending upon the final use of the harvested fruit. However, reducing the cost of olive harvest is of no advantage if the harvested olives cannot be successfully processed into high quality table olives or oil.

RECENT OLIVE MECHANICAL HARVESTING RESEARCH IN CALIFORNIA

California’s table olive industry is primarily based upon a single cultivar, the ‘Manzanillo’, processed in a style called “California black ripe”.  Much smaller amounts of ‘Mission’,  ‘Sevillano’ and  ‘Ascolano’ are also processed in this style.  The name is misleading as the fruit is harvested physiologically immature, therefore the abscission zone is unformed, and the fruit has a higher Fruit Removal Force (FRF) force than oil olives, which are generally harvested at physiological maturity.  Immature ‘Manzanillos’ routinely have an FRF as high as 1 kg when harvested.  When physiologically mature the FRF is less than 0.10 kg.  This immaturity, combined with the traditionally large trees, 4 – 6 m tall and 3 - m ft wide, and pendulous, thick growth habit of California’s irrigated ‘Manzanillo’ olive orchards makes mechanical harvesting difficult. 

Mechanical harvesting of oil olives has developed much more rapidly because new olive oil cultivars have been bred for slow growth, planted in high to super high densities, 486 – 1800 trees per hectare, and trellised or trained in a hedgerow that is easily harvested by over the row grape, coffee and blueberry harvesters. The olive oil industry pursued the long term goal of tree genetics, the mid term goal of new orchard conformations with hedgerow tree training and pruning, and the short term goal of adapting existing mechanical harvesters from other crops..  

Similarly, if the California table olive industry is to ultimately succeed it must also pursue tree breeding, new orchard conformation with hedgerow training and pruning, and mechanical harvesting technology. However, there is no current table olive tree breeding program in California and only one currently active in Spain.  Therefore, California’s table olive industry must pursue the short and midterm goals as follows.  For the short term this means developing a picking technology and tree pruning method for the current California table olive orchards.  For the midterm this means developing a picking technology and new orchard conformations, with new training and pruning methods.

Therefore, the focus of California Black table olive mechanical harvesting research for the last decade has been on dual objectives; developing successful mechanical harvesting for current and new orchards.  The effort has required the simultaneous input of University of California’s agricultural engineers, plant physiologists, food scientists, agricultural economists and horticulturists, California’s two major table olive processors, multiple commercial mechanical harvester fabricator/contractors, and the support of the California Olive Committee (COC).  The project included research cooperators from Spain and Argentina and has been conducted in California, Argentina and Portugal.  The project has had two distinct phases and a  long evolution as new harvesters have been evaluated and modified. Only the most recent summarized 2008 and 2009 research results will be given here.

a) Table Olive Mechanical Harvesting Research from 1996 through 1999.

The first phase was initiated in 1996 with a call from the olive marketing order, the California Olive Committee (COC) to harvest equipment fabricators for potential olive harvesters.  Agright of Madera, CA presented a modified wine grape harvester with a “canopy contact” head.   Research trials by Ferguson et al. (1999) from 1996 through 1999 demonstrated this picking technology was very efficient if the rods of the harvester head made direct contact with the portion of the canopy bearing fruit.  However, the rounded shape of a traditional olive tree rendered all but the portion of the tree canopy within the horizontal and vertical range of the picking rods, and facing the row middles, unharvestable.  The harvest head could remove up to 98% of the canopy fruit facing the middle of the row, but fruit above or below the harvester head, or in the canopy between trees, was removed with less than 50% efficiency.  Later versions of this machine have multiple heads that could move along a horizontal axis deeper into the canopy, slightly improving the overall harvester efficiency, (Fig. 1).  Additionally, the catch frames with the early iterations of the canopy contact head harvesters were incompetent, losing 19% of the fruit removed by the picking head.  This overall removal efficiency put final fruit harvester efficiency at approximately 60% or less.  Additionally, the fruit was often bruised and cut, Fig. 2, and unacceptable for processing as California black ripe table olives.  With the appearance of the olive fly (Bactorcera olea)) in 1999, mechanical harvesting research was discontinued.

b) Table Olive Mechanical Harvesting Research from 2006 through 2009.

Though most California table olive orchards are generally part of a diversified ranch operation, the increasing hand harvest costs, and stagnant olive prices of recent years, precipitated the removal of an increasing number of olive orchards.  The reason was the increasing table olive hand harvest costs were eroding profitability.  However, the United States is still the single largest table olive market in the world, giving California growers a marketing advantage.  Recognizing this problem, and the potential opportunity, the remaining olive growers organized for the resumption of mechanical harvesting research, again supported by the COC, in late 2005.    

When research was resumed the in 2006 there were two parallel and equal objectives.  The first was to develop an efficient picking technology.  Once this was defined, how to propel the harvester, catch the fruit, and convey it to a bin could be designed around the picking technology. The second objective was to identify an abscission compound that would decrease the FRF, and make the harvester more efficient. 

As the following results will demonstrate; two viable picking technologies have been identified.  However, development of an abscission compound remains as elusive as it has for the past 50 years. (Martin; 1994; Burns et al., 2008)  As the discussion of abscission in earlier in this manuscript concluded, development of an abscission in agent, much less obtaining a registration for a crop as small as olives, remains a goal not achievable within the next decade.  Both the California and international research from 2006 through 2009 have identified no new potential candidates and confirmed the earlier results that ethylene releasing compounds are as unreliable as previously demonstrated. (Burns et al., 2008; Martin, 1994)  As a result, the mechanical harvesters being developed for the California table olive industry need to achieve economic efficiency without the use of fruit loosening agents.

The two viable picking technologies currently being evaluated are canopy contact harvesting heads, and trunk shakers.  The canopy contact harvester can be successfully used in existing orchards that have been pruned to a hedgerow.  It can also be used for newer high density orchards trained to a hedgerow.  The trunk shaking technology can be used in new high density orchards with straight trunks but is ineffective in older conventionally trained orchards.  Interestingly, both have approximately the same final harvest efficiency, from 58% to 63%.  However, the mechanism of fruit removal is different, the two machines harvest different parts of the canopy more efficiently, and the potential for tree damage is different.  However, the final fruit quality as determined by grade at the receiving station of the olive processor is remarkably similar. 

Improving Harvester Efficiency with Orchard Modification

The new super high density olive oil orchards being developed in Argentina, Spain, Tunisia and California among others were all developed as orchards that could be harvested with existing mechanical harvesters; wine grape, blueberry and coffee harvesters.  All are straddle type harvesters with limited height and width.  

Our early research suggested high density hedgerow orchards could improve the efficiency of both canopy contact and hedgerow orchards. (Ferguson et al., 1999)  Efficiency would improve with canopy contact harvesters because the olives would be more accessible to the harvest head rods as shown in figure 4.  Efficiency would improve with trunk shakers because more of the olives would be closer to the axis of shaking, the main trunk.

 Based on this concept a high density hedgerow orchard with three different training treatments was established in 2002.  The objective was to produce a tree no more than 4 m tall, 2 m wide and skirted up to 1 m, and spaced at 3.7 m in the row and 5.5 m between rows with 490 trees/ha.  The training treatments were a free standing espalier with all the major structural branches trained within the tree row, an espalier woven vertically through three horizontal wires at 1, 2, and 3 m, shown in Figure 9, a treatment espaliered and clipped to the trellis wires, and a conventionally trained control.  The objective was to determine if these training methods decreased yields per acre. 

This orchard began bearing in year 4. None of the three trellised training treatments has a significantly decreased yield relative to the conventionally pruned control. This suggests ‘Manzanillo’ table olive orchards can be trained and pruned for mechanical harvesting with both canopy contact and trunk shaking harvesters without significant losses in yield.  However, data will be collected until the yields plateau for at least three successive years.

The next step in this ongoing research program will be to determine if the canopy contact harvesters and trunk shaking harvesters will have higher final efficiencies in high density hedgerow orchards, or in conventional orchards that have been topped, hedged and skirted to produce a modified hedgerow. These trials will be conducted in 2010.  At that time we also hope to determine the field operating parameters of ground speed, acres per hour, tons per hour and cost per ton and per hour to harvest the olives.  The final project goal is an online interactive harvest calculator which will allow growers to enter their orchard parameters to determine if hand harvest or machine harvest produces a better net return. 

CONCLUSIONS

Interestingly, though olives are one of the world’s oldest continuously produced tree crops the technology of production has remained unchanged through even the industrial revolution, a revolution that had a greater impact on agriculture than any other sector. Now however, the changes in olive orchard development and olive harvesting technology are bringing this traditional crop into the twenty first century.   Within ten years all truly commercial table and oil olives will be mechanically harvested. The research has been an ongoing process of defining, and ranking the limiting factors, while pursuing all of them simultaneously.  For table olives two picking technologies have been developed.  The most limiting factor, fruit damage, has been eliminated.  Now viable harvesting machines must be developed for both picking technologies and the orchards best suited to these harvest technologies must be defined. 

 For a complete set of images for this article, see

http://ceventura.ucanr.edu/newsletters/Volume_7,_No4_-_October-December_200929892.pdf