Fresno County raisin grower Jim Berekoff’s Thompson seedless grapes were softening in mid-June, but he wasn’t ready to shut down his powdery mildew control program, not until berries had reached full veraison. Barring any cool weather, that could happen by the end June, he says.

Powdery mildew pressure in his 60-acre, flood-irrigated vineyard has been about average this season. Very hot weather in early June seemingly ended the powdery mildew threat, but temperatures moderated later to the 70- to 85-degree range, ideal for growth of the disease-spreading spores.

“This is a very critical time,” says Berekoff. “If I back off now, the disease could bite me. If a number of grapes haven’t softened by the last week of June, I’ll treat again with sulfur dust or a fungicide spray.”

That should be it for the season, bringing his total powdery mildew prevention program to six treatments. Except for several applications of sulfur dust, most of these treatments combined a spray of wettable sulfur and a systemic fungicide.

“I do all the field work myself,” he says. “By combining both types of materials I’m not spending all my time on the tractor. And, I can irrigate without worrying so much about powdery mildew developing while water is in the field.”

Berekoff has been growing grapes near Kerman, Calif., for the past 30 years. Now semi-retired, he’s cut back his 130-acre raisin operation to the more manageable 60 acres. He leases out his remaining 70 acres of Thompson seedless.

Berekoff’s vines have been flourishing under ideal weather this year. “The weather has been good to them,” he says. “The vines are clean and look very healthy. The bunch count is good, and there are good shoulders on the bunches. After treating the vineyard with gibberellic acid at bloom, the berries are sizing up nicely. Right now, the crop size looks to be above average. If the weather turns real hot, though, they’ll start getting stressed.”

Insect pests like leafhopper and omnivorous leafroller haven’t been a problem.

“Over the years, most growers in the area have included an insecticide in their bloom sprays to control these pests,” he explains. “I think we’ve knocked down the populations to where there are not many out there.”

Despite a history of mite problems, the healthy condition of his vines this year could eliminate any need to control the pests this season, Berekoff reports. If not, he’ll treat them with a foliar applied with an electrostatic sprayer. It allows him to apply a fungicide using just 26 gallons of water per acre, about half the amount of water needed with a conventional sprayer.