Success in controlling relentless powdery mildew pressure this season, combined with unusually few insect pests, has resulted in nice-looking vineyards at Dwayne Cardoza Ranches, Inc., near Easton, and for other raisin growers in this area of central Fresno County, Calif.
“You can drive all over the countryside around here and everyone’s vineyard looks very lush,” says Dwayne Cardoza. “Except for mildew, they’ve been really clean of disease all season long.”
Cardoza has been growing raisin grapes since 1979 and has 200 acres of organic vineyards. About half the grapes, planted 10 years ago, are dried-on-the-vine DOVine variety. The rest — Selma Pete, Fiesta and Zante currants — are picked green and tray-dried.
Facing just a single disease threat to his crop up to this point in the year is unusual, Cardoza notes. In addition to powdery mildew, he and his neighbors often contend with phomopsis. Keeping powdery mildew at bay this year has been a long, tough battle, one that Cardoza waged from early spring until veraison began the first week of July.
“Every raisin grower around here was fighting mildew flareups this year,” he says. To control the disease he began dusting his vines with sulfur every seven days until early July, after which he treated with Kaligreen shortly before berries started softening.
Although, Cardoza usually needs to treat for omnivorous leafrollers (OLR), the only pest causing the slightest concern this season has been mites. “They haven’t been a real problem for me or other growers this year,” he says.
He once used various organic compounds to control mites, but two years ago he replaced those materials with six-spotted thrips beneficials, dispersing them at the rate of 2,000 per acre. They, along with other beneficial bugs, such as ladybugs, lacewings and spiders, have been effective in controlling the mites, he says. Cover crops of fava beans, oats, wheat and peas, provide habitat for the beneficial.
Cardoza’s vineyards are about two weeks later than normal in maturity, but he expects them to make up some of the lost time before harvest. Warmer daytime temperatures, which began during the last part of July, along with mild evenings, has reduced stress on the grapes, he says.
“We haven’t had a lot of 100-degree plus days, and that helps the grapes push a little harder. I don’t see us catching up all the way, but we may reduce the delay to about eight to 10 days.”
He’s plans to begin harvesting Zantes the third week of August and cut the canes on overhead trellises around Aug. 29, the same day he expects to start picking Selma Petes. Crews should be putting down trays Sept. 7-9. In the last week of July, a neighbor with the same varieties pulled sugar levels ranging from 11° to 17° Brix, he says.
A wide variation in berry size has him expecting average grape yields. The cool, wet weather this spring resulted in a late bloom that extended about four to seven days longer than the usual week to 10-day period.
“The range in berry size is all over the place,” Cardoza says. “I’ve noticed a lot of small berries and many of them won’t make raisins. I think we’ll pick more fruit than we’ll deliver this year.”