As the farm labor force in California continues to shrink and costs continue to climb, growers have been compelled to mechanize much of their farming tasks. Harvesting is one of the most labor-intensive tasks for California raisin growers, and fortunately, mechanical harvesting is an option for them. The technology has been around for quite some time now; however, some growers have been hesitant to convert to mechanized harvesting for one reason or another. For many, it’s a question of finance. Many of the old Thompson raisin vineyards are not set up to be mechanically harvested, but times are changing.
Total acreage harvested by mechanical means in 2018 was 45,429, nearly 30 percent of the State’s total raisin-type grape acreage, according to the Pacific Region Office of USDA’s National Agricultural Statistics Service. The Overhead Trellis Management System was used on 13,346 bearing acres in 2018, accounting for 8.8 percent of the total raisin-type grape acreage. Fresno and Madera County growers have 49 and 42 percent of the Overhead Trellis acreage in the State, respectively. Kern County growers have 6 percent of the Overhead Trellis acreage. Other mechanical harvest systems include Continuous Tray at 20 percent of the raisin acreage, South Side with 0.4 percent and Open Gable with about 1.2 percent of the raisin-type grape acreage.
Although Fresno County has the most acreage with mechanical harvesting, at 32,991, that acreage only represents 31 percent of the Fresno County raisin-type grape acreage. Kern and Madera County growers harvest 11 and 43 percent of their raisin-type grape acreage by mechanical means, respectively.
By variety, Thompson Seedless grape acreage with mechanical harvesting is 32,191 or 25 percent of the total raisin-type grape acreage. Fifty percent of the Fiesta grape acreage is harvested mechanically and 68 percent of the Selma Pete acreage is harvested mechanically.
Most California raisins are produced by sun drying after placing bunches on paper trays on terraces between vine rows. The Overhead Trellis System has led to increased production of dried-on-the-vine raisins, increased machine harvesting, and decreased hand labor use.
The Pacific Region Office of USDA’s National Agricultural Statistics Service, in cooperation with the California Department of Food and Agriculture, conducts an annual grape acreage survey. The 2018 Grape Acreage Report, published in April, summarized the latest survey results. At the request of the raisin industry, an additional question was added to the grape acreage survey form the past ten years to gather information on raisin-type acreage that is harvested mechanically. In addition to the mechanical harvest data, producers were asked to update acreage by variety and year planted. Growers were initially contacted by mail and follow up was done by telephone. This report summarizes data for mechanical harvest methods of raisin-type grapes. The totals included are only for those that voluntarily reported to this survey.
We sincerely thank the many vineyard operators, owners, and management for firms providing the information. Funding for the raisin-type grape acreage report was provided by the Raisin Administrative Committee.
Mechanical Harvest Methods
- Overhead Trellis–Grapes are dried directly on the vine, forming a canopy over the rows. It allows the mechanical grape harvester to get underneath and gather the dried fruit.
- South Side Trellis–In an east-west row orientation vineyard, an angled cross-arm is added to each trellis stake to support two wires on which fruiting canes are tied. The southern exposure of the fruit facilitates drying. The raisins may be harvested mechanically with a south side harvester.
- Continuous Tray–Grapes are mechanically harvested and laid out on a continuous (rather than individual) thin sheet of paper where they dry in the sun for two to three weeks.
- Open Gable – Trellis wires are connected between rows of v-shaped supports. The unique V-shape lets in additional sunlight and traps the heat. This greatly improves ripening and drying. Raisins are harvested mechanically with a harvester that has been modified to place the raisins in bins instead of gondolas.