Benefitting from unseasonably warmer weather, canes had reached about 18 to 24 inches in length and bloom had just finished by May 10 in the northern San Joaquin Valley vineyards served by Jim Alfieri, PCA with Wilber-Ellis. Based in Manteca, Calif., he works with wine grape growers in San Joaquin, Stanislaus and Merced counties.
Vine development has been running about a week or two ahead of normal. So has powdery mildew. He started seeing the telltale signs of the disease in early May.
“We’ve been able to find powdery mildew fairly easily on the leaves,” he says. “It hasn’t yet spread to the bunches. But, without proper treatment, it will.”
His program to protect vines from powdery mildew begins with a wettable sulfur and copper spray to reduce early-season inoculum when the canes are about 4 to 6 inches long. This year, that was around March 20. He followed this treatment 10 to 14 days later, when the canes had reached about 12 inches in length.
At the end of April and beginning of May, with foliage growth limiting effectiveness of sprays, Alfieri switched to dusting with sulfur. He applies the dust in rotation with different sterol inhibitor and strobilurin fungicides as needed until veraison.
By early May Alfieri was starting to see leafhoppers instars, which are common in his area. This spring he’s also been keep an eye on omnivorous leafrollers. Once fairly widespread in his growers’ vineyards, now it breaks out only sporadically, he reports.
In fields where the insect has posed problems in the past, he put out pheromone traps in March to catch the first flight. This year he started catching the moths around the first of April and the counts has been normal.
“We try to spray the vines before the bunches close, which would be around the end of May this season,” Alfieri says. “Otherwise, OLR can get inside the bunches to lay eggs. When the larvae come out, they’ll feed on the berries, opening them to sour rot infection.
Sour rot or summer bunch rot also occur in varieties with naturally-tight bunches as the enlarging berries crack, exposing them to disease-causing fungi. He sprays with gibberellic acid to prevent that on varieties for which that treatment is registered. He times that spray to reduce cluster compactness by reducing fruit set for about three weeks prior to bloom. In fact, that’s when he treated some Zinfandel blocks last month.
Except for some vine breakage caused by high winds in mid-April, this year’s wine grape crop is off to a promising start. “Everything is looking good,” Alfieri says. “Daytime highs have been between about 75 and 85 degrees. The vines like that kind of weather. With the right amount of water and fertilizer they just go.
“We’re seeing lots of bunches. Provided they all set, this should be a decent crop.”
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