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.

Hard times compared to other crops

Secondly, raisin farming has fallen on economically hard times compared to other permanent crops. Although raisin prices are at record levels of $1,900 per ton, other crops, like almonds, walnuts and pistachios, offer more profit potential at far lower costs.

It can easily cost $10,000 per acre to establish a simple two-wire Thompson seedless vineyard versus $6,000 to $7,000 for an almond orchard. And there is more hand labor in farming a vineyard than an orchard.

Long-time low prices for raisins are why 80,000 acres of raisin-type vineyards have been pushed and shredded in the past decade, despite escalating raisin prices. Yet, Thompsons are still coming out.

The move to continuous trays and DOV raisin production along with reduction in vineyards somewhat has eased the labor situation. It once took as many as 40,000 workers to hand harvest raisins. That need is down to about 20,000 workers. However, each year growers are worried they may not have enough workers to get the raisin crop in bins before fall rains. This past season, there was a season-long shortage of agricultural workers statewide, but raisin growers dodged the bullet once again thanks to the weather that allowed them to start earlier and go later into the harvest season.

However, there are grape growers who have invested in DOV vineyards and are committed to making it work. A small crowd of them and others interested in DOV gathered at a meeting sponsored by the San Joaquin Valley Viticultural Technical Group west of Fresno to hear four growers offer their take on DOV grape growing.

While there was a consensus on some practices, like it being imperative to put DOV vineyards on rootstock to ensure vigor, there seemed to be just as many differences, much of them evolving around trellising, pruning, positioning shoots and canes to solve one big problem.

“Shade is our enemy,” says Ben Letizia, a raisin producer from the Selma area.

He was joined by fellow DOV growers Ron Kazarian of Circle K Ranches in Fowler, Trent Hammond whose family farms in the Biola area and Ron Brase from Rolinda.

The panelists often looked like mimes trying to explaining the various vegetation management systems of pruning and cane placement and cordons. The one thing that has been clear is that there has been plenty of on-farm experimentation.

Kazarian may not have been sold a bill of goods seven years ago when he was told he could get 4 tons of raisins per acre at half the labor costs of traditional raisin production. However, it has been seven years of “frustration” to fill that bill.

University of California viticulture farm advisor for Fresno County, Stephen Vasquez, detailed research work at the meeting he has cooperated on with UC viticulture specialist Matt Fidelibus, based at the UC Kearney field station in Parlier.

Holding back shade

Excess leaves shade causes bud death and impacts bud fruitfulness, he says.

“DOV systems are planted to very vigorous vines, and that is the biggest problem,” he says. It takes precise irrigation and fertilizer management to throttle back this vigor.

Growers need vigor to cover the massive trellis systems and most of the DOV vineyards are on rootstock to encourage that vigor.

However, too much of a good thing creates a jungle and vines suffer underneath the blanket of leaves, many of which never see sunlight and fall on the vineyard floor.

”This is a huge negative,” he says. Not only does shade impact this year’s crop, but it can impact developing buds for the next year’s crop. There are basically two crops on a grapevine at the same time, Vasquez said. Mess up one year, and you could mess up two crops. DOV systems are far more labor intensive to prune and manage.

“You need a more technical pruning crew. You really have to think to train a DOV system. You have to set up the vine differently to where the canes lay out,” Vasquez says.

DOV systems require as many as 30 man hours per acres just to properly select and prune wood. This is roughly double the cost of a traditional two-wire Thompson system.

There was a wide array of trellising systems described by the four panelists, including a very unique looking cordon created by Brase. He twisted two canes together like two ropes to make a single cordon. Vasquez said that came from Australia.

Kazarian said trellising is a long-standing subject at growers’ coffee shops. Several certainties emerged from the panel:

--Grafting a DOV variety to a Thompson seedless stump is not a good idea. For one reason, DOV vines use high amounts of potassium and Thompson roots cannot pick up enough K to satisfy the DOV varieties.

--Controlling powdery mildew from the first year of establishment is critical, especially for Fiesta, which is particularly susceptible to powdery mildew.

--Leaf thinning is an option for reducing a vigorous DOV canopy.

--Cut canes early ahead of harvest. Wait until after Aug. 15 and you may have to book dehydrator time. Hammond has set up an on-farm drying house in an insulated building with heaters to finish drying down at least some of the raisins each year. He dries them in half full raisin bins.

--A zinc application is critical two weeks prior to bloom. Without it clusters will be scraggly, with shot berries and low quality fruit.

--Selma Pete must be pruned to longer canes to get the 15 nodes necessary for a crop.

Although it has proven challenging, DOV raisin vineyards are likely here to stay for those who stay with raisins. Vasquez said USDA-ARS plant breeder Dave Ramming continues to develop varieties perhaps more suited to DOV production.

“Growers will continue to experiment in their own vineyards and that is good,” said Vasquez, who indicated UC will continue its research efforts, as well.

However, he added it will take grower commitments to continue producing raisins in any system, when other alternative crops may be more financially appealing.