Powdery mildew pressure heavy in raisin vineyards

Powdery mildew pressure heavy in raisin vineyards

Warm weather had pushed Huter Farms’ Fresno County raisin grape crop as much as 10 days ahead of normal.

This spring’s sunny, unusually warm weather had pushed Huter Farms’ Fresno County raisin grape crop as much as 10 days ahead of normal.

“The vines are looking good, and veraison is just around the corner,” says E.G. Huter. He and his father, Elmer, Jr., grow 360 acres of Thompson seedless grapes near Kerman, Calif.

Like other growers in the area, the Huters expect to harvest a sizeable crop this year. By contrast, their 2012 tonnage was one of their lightest crops in recent memory. 

Shatter this season occurred in their vineyards in mid-May. “We like to do a little thinning and sizing of the grapes with gibberellic acid added to a fungicide spray at late bloom.  Right now, the clusters are nice and long with an oblong shape to the individual grapes.” Overall, it was a nice shatter which should result in plump raisins.

He expects berry softening to start before the end of the month. Normally, veraison doesn’t begin in the Huters’ vineyards until after July 1.

Except for a week of cooling in early May when the vines were blooming and later over the Memorial Day weekend, temperatures have been running well above normal – including the first weekend of June, when thermometers in the Fresno area reached 108 degrees. It’s normally July before growers see 100-degree days.

The hot weather is a double-edge sword. It is moving the grapes ahead of schedule, but it is also heightening demand early for water, which is in short supply this season.

Ditch water from the Fresno Irrigation District is being reduced 40-percent from a normal water year. Water deliveries didn’t start until the first week of May and are scheduled to continue only through July.

The delay in water deliveries prompted them to start pumping water from their wells in March. In years of adequate rainfall and snow in the mountains, pumps would be idled, even after harvest with a ditch water run until October.

This year, the Huters were able to supplement water supplies with reclaimed water from the City of Fresno. That water is cheaper than pumping, but with a limited supply the wait list is long.

Like other raisin grape growers in the Kerman area, the Huters’ vines have been under heavy powdery mildew pressure this spring. “The Powdery Mildew Index has stood at 100 for at least a month,” E.G. says. He credits their regular treatments of wettable sulfur and rotating fungicide chemistries with keeping the disease under control.

The Huters prefer the wettable sulfur form in a tank mix with fungicides. “It costs more, but it’s easier to work with.  We think it provides more effective and longer control,” E.G. says.

The most recent powdery mildew sprays included a miticide. “Spider mites have been reported in the area, but they haven’t caused any major problems,” he says. “We haven’t seen any yet in our fields and want to prevent a blow-up.”

Labor issues

The Huters have been using machines to harvest all but a few of their grapes for more than a decade. They farm a 10-acre piece of north-south rows that isn’t suited to mechanical harvesting. They normally have available 12 men and women cutting canes and operating the harvesting equipment.

“As harvest draws closer, we will decide if we need to find a contractor for the 10 acres or go with our own crew,” E.G. says. “The industry, as a whole, is struggling to get enough labor for harvest; hand picking takes up a lot of profit, it’s a killer. We’re never going back to hand picking our grapes.”

If you would like to read more about California grape growing, subscribe to GrapeLine, the exclusive electronic newsletter sponsored twice a month by Chemtura. To sign up, go to the Newsletter Sign Up box on the Western Farm Press home page (westernfarmpress.com). It’s free and e-mailed the second and fourth weeks of each month from March through October.


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