In the 26 years that Merced County, Calif., grape grower Steve Moeller has been producing raisins from Thompson seedless grapes, he’s learned a thing or two about making a good crop. One of the most valuable lessons has been: Don’t try and fix what is not broken.
“I’m always looking for an opportunity to improve our operation,” he says. “But, what we’re doing works for us and we’re making money, so I don’t see us changing our practices a lot in the years ahead.”
At the same time, the location of his furrow-irrigated vineyards — near Livingston in Merced County — pretty much limits his agronomic flexibility. They are at the northern limit of sunlight intensity and climate suitable for making raisins.
Moeller’s two Thompson seedless vineyards, totaling 18 acres, date back to 1928 when his wife’s grandfather planted the first vines. The hand-picked grapes have been made into raisins, using single trays, every year since the first harvest.
“If a winery doesn’t want your grapes, what else can you do with a perishable crop?” he asks. “With raisins, I can control my destiny a little more by reconditioning them, if necessary, after harvest.”
Given his location, spring frosts are always a threat to his crop, and chances of getting rain on his drying grapes are also higher than for growers farther south in the valley. Moeller has established a respectable record in managing those risks. Typically, his yields exceed 2 tons of raisins per acre.
“There have been very few times when we haven’t had a good crop,” he says.
One reason for that success has been consistency in following his production schedule.
“As far north as we are, we can’t change our routine for making raisins a whole lot. If your timing isn’t right, you could have a lot of problems.”
For example, he tries to lay his grapes on the ground by Sept. 1 in order to provide sufficient drying time before rain chances increase too much. Waiting a few more days for sugar levels to increase isn’t worth the risk, Moeller says. This past season, however, because of delayed maturity of the grapes, he postponed putting them on trays for three days.
Usually, the raisins are ready to pick up 14 days after the grapes are put on the trays, but this year he let them dry an extra three days. The timing was close: rain fell on his vineyards the following day.
Moeller’s fertilization program includes the use of chicken litter, spread at the rate of 4 tons per acre in February. He started this practice not long after he began growing grapes to deal with a nematode problem. “This compost has rejuvenated the vines,” he says.
He makes his first irrigation as soon as water begins flowing through irrigation district canals in the spring, usually around the first of March, and continues every 10 to 14 days until the Fourth of July.
“I cut off the water as soon as the grapes reach veraison,” he says, and then the vineyards receive no water until harvest. That stresses the plants, causing them to make more sugar. The vines aren’t hurting, though; every time we disk in July and August, we’re still bringing up moisture.”
He aims for 21 to 22 sugar points in his grapes at harvest. Immediately after the raisins are picked up, he gives the vineyards a good irrigation so they will go into winter with plenty of subsoil moisture.
Moeller switches among various fungicides to control powdery mildew, and to keep phomopsis cane and leaf spot in check he makes three applications of wettable sulfur: when the plant shoots begin growing, when they reach 8 to 10 inches in length and again at 21 inches. From then on he makes applications every three weeks until he stops irrigating July 4. This approach saves time compared to using dry sulfur, which has to be dusted on the vines every 7 to 10 days, he says.