TULARE, Calif. — As recently as 10 to 15 years ago, Labor Day signaled an end to large table grape volumes, and prices responded by climbing.

But now, Labor Day marks the beginning of the second half of the season, thanks in part to later-maturing varieties and production systems that rely on plastic covers to protect the grapes from fall rains, said George Matoian, sales/marketing, Visalia Produce Sales Inc., Visalia.

Sundale Vineyards, Tulare, has invested heavily in plantings of the late-season autumn king, a large, green seedless grape, as well as late-season crimson red and Sundale Red — large, red seedless grapes, said Sean Stockton, president.

“What’s driven our success is the late-season deal and our extensive covering program,” Stockton said. “We’ve done it every year in anticipation of a wet season.”

Historically, the first rains of the season in the San Joaquin Valley occurred from mid-September to early October. That was one of the main reasons why most San Joaquin Valley table grape growers exited the table grape deal after Labor Day to avoid the risk of having fruit still on the vines, said Matoian, who also grows table grapes.

Fall rains can prompt fungal growth on the berries, requiring costly hand-trimming during harvest. Under the worst conditions, entire bunches can be lost to rot or other fungal diseases.

Newer varieties, such as red globe, autumn royal, autumn king and crimson, don’t even really get started until late summer.

“If you look at the table grape numbers, a major part of the volume is now harvested through the end of September, October and November,” Matoian said.

Stockton called the autumn king a game-changer.

“We haven’t had a variety, other than the 16-pound thompson that was harvested in August, for your Thanksgiving shelves,” he said. “Now we’re harvesting the autumn king in late October and early November that are three or four weeks old for your Thanksgiving shelves. It extends the season out of California all the way to Christmas.”

Most growers now cover their vines with plastic sheeting, beginning in September — “rain or shine” — to protect them from possible rainstorms, said Max Jehle, an independent consultant with Max Ag Consultants Inc., Visalia.

Using machines built in-house, Sundale begins covering the vineyards Sept. 1 and typically finishes the third week of September, Stockton said.

The program allows Sundale to hold the varieties on the vines through much of the fall without the damaging effects of rain.

“It’s been incredibly effective for us to weather those storms and have fresh fruit that we’re able to pick late in the season,” Stockton said.

Depending on the trellis design, the plastic and labor to apply the material together can run $600-$1,000 per acre, Jehle said.

Some growers will apply it as a tube over the top anchored at each end. This allows for sun and airflow on the sides. At the threat of a storm, workers pull down the sides over the vines.

If the forecast calls for an extended dry period, workers can lift up one side to reduce moisture condensation, which could promote fungal diseases, under the plastic.

Each time the plastic is rolled up or down adds to labor costs, Jehle said.

Because of the thinness of the plastic, it can’t be reused the following season, he said.

Matoian admits using the plastic covering is expensive, but he said the alternative is even more costly.

“If you have adverse weather conditions, you could lose the crop,” he said.