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.