Autumn King was developed by USDA’s Agricultural Research Service horticulturists and released five years ago. The work was directed by ARS Horticulturist David Ramming, based at the ARS San Joaquin Valley Agricultural Sciences Center near Parlier, Calif.

Rather than calling Autumn King a green grape, he identifies it as a white grape to avoid any misperception that the word green refers to an immature grape.

“Growers are quite enthusiastic about Autumn King because it has larger berries, higher yields and ripens later in the season that Thompson seedless,” he says.

In the Fresno area, Autumn King can be picked starting the first part of October and marketed fresh through the Christmas holidays, Ramming says. That’s a big plus compared to Thompson seedless. Harvested in August or, the very latest, in September, Thompson grapes must be kept in storage for the December holiday trade. As a result, this past season Autumn King attracted good prices, he reports.

Autumn King berries are big, too. “It sets the new standard for berry size,” Ramming says. Autumn King berries, which typically weigh about 11 to 13 grams each, are twice as large as those of commercial Thompson Seedless table grapes, which are normally about 5.5 to 6.5 grams. Unlike Thompsons, Autumn Kings reach the large size naturally, without a gibberellic acid treatment.

Depending on how the vines are planted, trellised and clusters thinned, the cane-pruned Autumn King can produce 1,000 boxes or more per acre, he says. That compares to about 800 boxes per acre for Thompson on a double-T trellis and around 1,200 boxes per acre when grown with a gable trellis.

Autumn King is only the latest in a number of red, black and white varieties developed over the last 64 years by the ARS grape breeding program in California. They include the seedless varieties Sweet Scarlet, Scarlet Royal, Flame Seedless, Crimson Seedless and Princess.

In fact, Princess, a white mid-season grape released in 1999, is the only public variety that competes with Thompson seedless, the long-time industry standard for white grapes. Currently, Princess ranks eighth in terms of acreage of all table grapes planted in California.

Without the use of gibberellic acid it produces the same size berries as Thompson seedless that has been treated with the growth hormone. However, with gibberellic acid, Princess berries usually weigh in the 8 to 9-gram range.

“There’s no perfect variety,” Ramming says. “Sunburn can be a big problem for Thompson, but not for Princess. However, Princess is a vigorous-growing grape and should have plenty of cover to protect it from sun exposure.”