“This is a nice time of year to be in the vineyards — they look really good,” says Fresno County, Calif., raisin and wine grape grower Don Hornor “The weather has been cooperative, and with the recent above-normal temperatures, vines are growing super fast.”
Hornor Farms, located near Kerman, grows 800 acres of Thompson seedless and 120 acres of Zante currants, along with 300 acres of Rubired.
The promising picture he describes for May is far different from what he was seeing earlier. This past winter — for the first time in more than three decades of growing grapes — he flood-irrigated vineyards twice, once the week before Christmas and again in lateFebruary. They then received no precipitation until March.
“In some years, we’ll do one irrigation, or maybe run water down every other row,” he says. “But nine out of 10 winters, we don’t irrigate at all.”
Early April brought another unusual weather event. While at the local coffee shop one morning, several growers mentioned that their pickup thermometers showed readings in the range of 32 to 34 degrees. “Since they weren’t talking about temperatures of 30 degrees or colder, I didn’t think anything of it,” Hornor recalls. Two days later, his foreman reported what he thought was sulfur burn on some vines. When Horner went to look, from 20 percent to 80 percent of newly-forming grape bunches had been damaged in about half his fields.
Overall, raisin industry observers believe there was about a 3 percent crop loss from spring hail and frost.
Hornor’s hardest-hit blocks were those recently in preparation for an irrigation. About a fourth or more of bunches in fields with cover crops were also damaged. Ironically, just across the road from those fields, vineyards being irrigated during the frost escaped injury, without even so much as leaf burn, Hornor says.
“Just a foot or two difference in elevation within the same field was the deciding factor in whether or not bunches got frosted. In areas with the worst damage, bunches which were out about two to three inches were totally frosted and black. This is my 37th year of producing raisins, and I’ve never had this kind of frost damage. In some fields, we’ll probably pick only about a fourth of the grapes that we normally would.”
Although damaged vines have since produced new shoots, fruit formation has been minimal, with no more than about 10 percent of the vines developing new bunches, Hornor says.
So far, powdery mildew pressures fields are much lower than a year ago. “Last year, with late spring rains and higher humidity, was horrible for powdery mildew,” he says. “It was the worst ever — we were spraying every week. It seemed like everyone was battling the disease.”
This year, even though temperatures in the first part of May were conducive to growth of powdery mildew, winds and lower humidity have helped keep the disease at bay, he says.
His powdery mildew control program begins with one or two applications of wettable sulfur, depending on his irrigation schedule, when new shoots are in the range of 6 to 18 inches long. Once bunches have stretched out and are starting to be covered by leaves, he switches to dusting sulfur for better penetration.
Due to the unusually heavy powdery mildew pressure last year, he’s dusting vines about every five days this season. Normally, he applies the material every 7 to 10 days, alternating the dusting sulfur with an application of a sterol inhibitor, which provides about 14 to 18 days of control. He continues this cycle of treatments, which is fitted around his irrigation schedule, until verasion in mid-July.
In the latter part of May, he includes a preventive miticide spray with the fungicide treatment.
“Mites can be pretty bad,” Hornor says. “The best way to control them is to prevent them. One miticide treatment is good for about 30 days. We’ll keep monitoring, and if there’s a problem we will treat again with a stronger material.”