During the last half of August, field crews walked the rows of Philip Hagopian’s Thompson seedless vineyards near Madera, Calif., dusting vines with sulfur or clipping off bunches wherever they found signs of possible botrytis outbreaks.
Hagopian’s flood-irrigated vineyards include 250 acres of Thompsons, which he grows for raisins, as well as small blocks of wine grapes — Black Muscat and Riesling — and Flame Seedless and Red Globe table grapes. He also grows 80 acres of almonds.
Earlier in the season, about a third of his Thompson acreage suffered heavy pressure from powdery mildew in parts of three of his four raisin grape blocks. Cracks or splits in the infected berries left the grapes vulnerable to entry of the botrytis organisms.
Hagopian first noticed botrytis decay in his grapes at mid-August, particularly in areas along pipelines and at row ends where water accumulates.
“We’ve been checking the areas where we had problems with powdery mildew for any signs of rot,” he says. “We’re not finding too much, but where we do, we want to get it out.
“Mildew overwintered in some of our fields. That, coupled with weather conditions conducive to growth of mildew, made it really tough to control the disease in those areas.”
During the spring, he dusted his Thompsons regularly with sulfur to head off mildew. But after seeing mildew on some berries, he cranked up his control program a notch or two, increasing sulfur application rates, adding treatments with other mildew-fighting materials such as potassium bicarbonate and a sterol inhibitor fungicide, and reducing or delaying his water applications in an attempt to discourage development of the disease.
“We stopped the mildew to some extent, but we weren’t fully successful,” Hagopian says. “We’ve had losses — right now, I just don’t know how much. We’re trying to minimize any decay in the grapes from botrytis. I’m not sure exactly how the fruit will look coming off the vine. Hopefully, we can get everything harvested and stay under the packer’s 5 percent mold limit.”
He expects his 2011 raisin crop to be bigger than last year, but mildew limited the size of berries where it was a problem this year. “If the stunted berries don’t crack, they should have fairly intense flavor because of relatively higher sugar levels. So, they should still have good quality.”
Hagopian planned to start hand picking three of his Thompson Seedless vineyards Sept. 9, four days later than last year. He planned to also cut the vines in his one mechanically harvested vineyard that same day.
His goal is to get his single trays of raisins off the ground by the insurance deadline of Sept. 20 for the hand harvested crop and to pick up his continuous trays of machine picked grapes by the Sept. 25 deadline.