Mechanical Harvesting of Blueberry
Interest in mechanical harvesting of blueberries has increased lately as new labor regulations have been enacted, and as over-the-row mechanical harvesting technology has become more refined. Not all fields can be mechanically harvested, however, with self-propelled harvesters. Generally 10- to 11-foot rows and 25-foot headlands are needed to maneuver the machines. Ground with a slope in excess of 10 percent presents difficulties. Plants need to be pruned annually in order to prevent the formation of twiggy growth and keep the crown narrow.
Hedgerow plantings are most conducive to mechanical harvesting. Growers have tried to restrict the base of the crowns and erect trellis wires in order to keep the bushes relatively narrow. In research trials, narrowing the crown reduced ground loss through the catch plates on the harvester, but also reduced overall plant yield as a result of loss of fruiting wood. Excessive weed growth at the base of the plants will need to be controlled as it can seriously interfere with catch plates.
In the Northwest, mechanical harvesters are either purchased, leased, or rented for the harvest season from machine manufacturers. As a general rule, a minimum of 10 acres of producing blueberries is required to justify the expense of purchasing a self-propelled machine. In order to further amortize the expense of operating a harvester, growers will custom-harvest other fields or other crops such as blackberries and raspberries.
Early attempts at utilizing machinery to harvest blueberries centered on the use of hand-held vibrators (battery or air compressor powered). Canes are bent over a portable catching frame and vibrated with short bursts in order to dislodge the ripe berries. Problems with this harvesting method include having to run the berries through an air separation unit to remove the large amount of debris that is collected.
In the past 10 years, design engineers and manufacturers have made significant strides in improving self-propelled, over-the-row mechanical harvesters. The first harvesters had a slapper-type picking mechanism where metal rods “slapped” the bushes from both sides. On slapper machines, dislodged fruit falls to the base of the machine where it is caught on sloped catch plates. Berries then roll to a conveyer belt that runs towards the back end of the machine. A cup conveyer belt moves the fruit up to the top of the machine where it is sent past an air blower to remove trash and then onto a second conveyer belt that passes past an operator for inspection prior to filling a plastic processing flat.
There are a number of problems inherent in the slapper principle. If the machine is driven too quickly through the plantation, a significant amount of fruit (15-25 percent) can be lost on the ground behind the machine. Because of fruit bruising, most of the harvested fruit has to be sent to a processing outlet. Branches can be broken off or scarred, allowing entrance of disease organisms. Even with a properly adjusted slapper machine, there is still a considerable amount of over-ripe or green fruit that will have to be sorted out by graders in a processing line.
The next advancement in harvesting technology came with the introduction of the sway-type picking mechanism. In this arrangement, a forward set of rods works in coordination with a rear set of rods in the middle of the picking tunnel to compress the bush and “sway” it from side to side to dislodge the berries. Sway machines work very well on trellised crops such as red raspberries, or free-standing, low density bush crops. In mature blueberry plantings, however, growers have found that the bushes tend to become compressed excessively within the tunnel. After the machine has passed a bush, the recoil of the stems results in a loss of both ripe and green berries behind the machine onto the ground.
Fruit from sway machines generally has to be processed. Recently one manufacturer introduced a small version of an over-the-row sway harvester that is pulled behind a tractor and powered by the PTO shaft. At a price of approximately one-fourth of the larger self-propelled machines, this machine will probably be best suited to younger, smaller plants.
The most recent and successful harvester technology is based on the rotary head principle. On either side of the picking tunnel, a revolving drum with multiple nylon beater wands turns with the forward motion of the harvester. Drums either travel horizontally or vertically (depending on the machine manufacturer) to shake the fruit off the stems, where it falls to the conventional fish plate and conveyer belt system below. Rotary machines impart the least fruit bruising and stem damage of all the different machines available. As yet, no estimates of harvest loss have been made on the newest rotary head machines. One manufacturer has introduced automatic steering on its machine to further reduce loss through open catch plates; the machine is centered on the base of the plant which the driver cannot often see. Still, machine operators need to be well-trained and follow the manufacturer’s recommendations for efficient harvest.
With a properly adjusted rotary machine and selection of cultivars, growers may be able to machine pick the first one to two harvests and sell the fruit fresh. However, machine-harvested fruit for the fresh market should be sold quickly since it has a very short shelf-life. Later pickings usually have to be processed.
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University. How to Order