California’s central San Joaquin Valley growers thought they had it made in the shade when mechanically harvested dried-on-the vine raisins were promised to produce as much as twice as many raisins per acre at half the labor cost.

Who wouldn’t be all ears, if someone promised that overhead and open gable trellising systems would produce 3 to 5 tons or more raisins per acre that never touched the ground for sun drying.

However, those promises have turned out to be a bit jaded by shade.

Originally developed in the 1970s in Australia where labor is shorter than the kangaroo’s front legs, drying raisins on the vine (DOV) and gathered by machine began to catch the fancy of California raisin growers about a decade ago. Growers initially were not interested in DOV, partly because there was no economic incentive when labor was relatively plentiful and inexpensive. Also, Thompson seedless, the long traditional raisin variety grape, did not adapt well to the big, sprawling trellising systems. Producers were content with 2-tons per acre average yields from traditional two-wire, field-dried Thompsons.

However, as labor became scarcer by the season, growers warmed to the DOV idea.

DOV is the next step after the first successful mechanical raisin grape system, machine harvested/continuous trays, which is still the most popular labor-saving way to produce raisins. This involves cutting canes holding green grapes a few weeks ahead of harvest and letting the grapes partially dry on the vine and before laying on row-long paper trays the with modified wine grape harvesters. This can be accomplished in traditionally trellised vineyards.

A DOV vineyard is far more expensive to establish and prune, but promises to yield of 4.5 to 5 tons per acre for an overhead trellis that completely covers the vineyard, much like an arbor, and 3.5 to 4 tons of dried raisins on the open gable system which spreads out the vine canopy very wide over the vines, but does not close the middles. You can still use conventional farm equipment to farm open gable, but it requires special equipment to farm the overhead trellis, particularly the harvester.

Bolstering the DOV evolution has been the development of early drying raisin varieties, Divine (released in 1995) and Selma Pete (released in 2001), that are vigorous enough to produce the tonnage promised. Fiesta, a raisin variety released in 1973, was tossed into the DOV equation due to its high vigor.

There are slightly fewer than 20,000 acres of DOV trellising systems in the Central Valley, where all of California’s raisins are produced. Virtually 100 percent of the U.S. raisins and 45 percent of the world’s crop are produced within a 60-mile radius of Fresno.

DOV represents less than 10 percent of the total raisin-type acreage, and it’s not growing much, despite continual labor problems and record raisin prices. Most of the existing DOV vineyards are either Fiesta or Divine varieties. However, the newer Selma Pete has become more popular for DOV.

DOV has not taken off as many had expected for several reasons. One is the cost of the trellising system. A grower can easily spend $12,000 or more just for stakes, wire and hardware. That is roughly double a conventional vineyard.