As fall approaches, Fresno County, Calif. raisin grower Ken Shinkawa is casting one wary eye at his slow-to-mature Thompson seedless raisin crop and another at his calendar as the date edges ever closer to the Sept. 20 insurance deadline for machine picking grapes onto raisin trays for drying.
Also a concern is the ever-present field chatter about possible labor shortages.
Shinkawa’s 120 acres of vines north of Caruthers, Calif., are “a good two weeks later than I’d like to see,” he says. “Maturity is so late this year that growers will want to hold off harvesting as late as possible — which means a pretty small window to harvest grapes without weather damage.
“Those who normally work for me report that the supply of labor is short, not just in California but also for apple growers in Washington. A lighter labor supply and a shorter harvest window will put quite a bit of pressure on grape growers and labor contractors to get the job done in a timely fashion.”
A smaller-than-expected California crop may help ease that pressure somewhat. The USDA’s National Agricultural Statistics Service predicts California growers will harvest 2.05 million tons of raisin grapes this year — down nearly 7 percent from the July forecast. This year’s bearing acreage is 210,000, the same as last year. The 2011 California Raisin Grape Objective Measurement Report describes the 2011 crop as shaping up to be of average size.
For Shinkawa, the maturity of his grapes is not only late, it’s also variable — even within clusters.
“Clusters have more berries of different sizes than usual,” he says. “Some berries are achieving sugar, while others on the same cluster haven’t softened yet.” He attributes this to erratic spring temperatures that prolonged the bloom.
In early August, he began seeing a little powdery mildew developing in a few spots in his vineyards. Fortunately, he’s been able to contain what could have been a serious threat to his grapes by starting his mildew control program early.
“Early is really your only chance to control mildew,” Shinkawa says. “Once the clusters tighten with berry swelling and the full canopy develops, it’s very difficult to get good spray coverage to prevent the disease.”
He begins his disease control program to prevent phomopsis when he sees green tissue, applying cupric hydroxide and wettable sulfur. He tries to spray prior to rainfall. This program, which protects against phomopsis lesions and cracking, also helps provide early control of powdery mildew.
Once temperatures warm to the point mildew can become a problem, he rotates various fungicides with different modes of action to prevent development of fungicide resistance, and adds wettable sulfur to every load of spray. He’ll treat until veraison.
Mildew could still be a problem on grapes that had not softened by early August, if the weather stays cool, he notes. “Any mildew that formed on these small berries could move up the rachis and slow maturity of the whole cluster. But, it’s so late in the season, I don’t think that will happen.
“I’m hearing of vineyards where berries that had mildew early in the season are now splitting. That happens because the affected tissue doesn’t expand as the berry grows bigger. Those splits can increase the risk of bunch rot developing in the cluster.
Sugar in his grapes is coming up very well, he says, and assuming no big heat spikes to slow the process, he expects his vineyards will be ready for cane cutting Aug. 26 for vine drying for machine picking. That’s three to seven days later than he likes. However, he’s not sure the grapes will reach the desired 21° Brix by then.
Two weeks later, he’ll bring in the grape harvester. He expects to start picking up dried raisins about 8 to 10 days after picking.
Until then, Shinkawa is waiting and watching. “By now, I’ve done everything I can do to reach harvest,” he says.