Tweaking dried-on-vine raisin production

Like many raisin producers who have adopted dried-on-vine (DOV) systems, Benjamin Wilson continues to learn how to make the most of the reduced labor method of making raisins.

Wilson, of Handel and Wilson Farms, Shafter, Calif., converted his first conventional vineyard to DOV 10 years ago, harvesting his first DOV raisins in 2001.

“We’ve made changes in our approach every year, as we learn which practices work and which don’t,” he says. “The jury is still out as to whether DOV or continuous tray is most profitable for us.”

Except for one block of Selma Pete, most of his grapes are Thompson Seedless.

Earlier this month, Wilson described the condition of his Thompsons as “decent, but not stellar.” Following last year’s high yields, he expects production to drop 15 percent this year to a more average level.

Based on bunch counts, however, his 2009 Selma Peter crop appears much more promising. “They look outstanding — it could be the biggest crop we’ve seen on this ranch. These vines are just coming into production; some are in second leaf and others in fourth leaf. The open-gable trellis gives them a little more space to develop.”

His biggest challenge with DOV is controlling the amount of crown fruit. Unfortunately, that requires hand labor.

“That’s frustrating, because one reason for going to DOV is to reduce hand labor costs,” Wilson says. “Every time you send workers into the vineyard, you’re killing your profit-potential.”

Seven to 10 days after cutting the canes, he’ll hang the crown fruit on wires to dry with the other grapes. Then, when mechanically picking the DOV raisins, a worker on a trailer behind the harvester pulls out any remaining crown fruit.

“We do whatever is necessary to keep the green percentage low enough to prevent fermentation and rotting, but we’ve never got it down to zero percentage,” he says.

Wilson grows his grapes on an open-gable, Sun-Maid south side and on T-trellis systems. The more open the DOV canopy in the Selma Pete, the easier it is to pick the fruit.

The later maturing Thompson Seedless poses another challenge. “We’re always fighting to get them dry enough before the weather starts working against us in the fall,” Wilson says. “On the other hand, using DOV with Selma Pete on an open gable trellis is a slam dunk, if you want to invest in that type of trellis.”

Another practice Wilson varies from year to year is the use of gibberelic acid to speed maturity and improve bunch shatter.

“The times we’ve had good shatter, we haven’t had as much bunch rot,” he says. “Last year, the only block we didn’t treat with gibberrelic acid had bunch rot. This year we treated all blocks. Timing of the application is critical. Some years we get a nice shatter, some years it’s only so-so.”

TAGS: Grapes
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