California wine grape growers long ago traded bushy canopies for sleek trellising systems, but they continue to discover the importance of managing the vineyard canopy to optimize light conditions for maturing grapes.

Table grape vineyards were the primary model for the vineyards serving California wineries until the early 1980s, said Dr. Nick Dokoozlian, vice president, viticulture, with Modesto’s Ernest & Julio Gallo Winery, during a presentation at the annual British Columbia Wine Institute viticulture conference in Penticton, Canada, last summer.

Vineyards were planted on 12-foot by 8-foot spacings, but the sprawling canopies of the vigorous vines prevented the maturing fruit from getting much light. Researchers found that California wine grapes enjoyed less than 1 percent ambient light—less than any other crop then in production.

While ambient lighting, or sunlight energy, of up to 20 percent a day helps grapes mature and ripen, California’s vines were seeing nothing near that amount of light. The result was high-yielding vines producing low-quality fruit that lacked color, flavor, and the phenolic compounds that enhance wines’ appeal to the palate.

“The part of the canopy in which we needed light in order to get adequate fruit load as well as ripen our canopy was the darkest part,” Dokoozlian said. “We definitely had a problem.”

During the 1980s, growers reconsidered row spacing and introduced cultural practices such as shoot thinning and leaf removal that have since become standard. The changes opened up the vines to more light, and the quality of California wines started to improve.

But when type-B phylloxera hit in the late 1980s, the industry went into a tailspin.

The disease led to the removal of tens of thousands of acres of vines. What was otherwise a disaster for the industry gave growers a chance to replant their vineyards based on their new understanding of the importance of lighting to the canopy and fruit.

The new vineyards were denser, with 8-foot by 5-foot or even 8-foot by 4-foot spacings, and vertical shoot positioning trellising systems became commonplace. Attentive management focused on controlling vine vigor and ensuring grapes were getting enough light.

“We got to retool our entire industry,” Dokoozlian said. “In 1989, there was not one, not one vertically shoot-positioned vineyard in the Napa Valley. Now, if you go there, you can’t see anything but VSP vineyards, for the most part.”

Vertical trellising increased the clusters’ exposure to sunlight, but it also reduced the shading the grapes enjoyed, warming up the clusters. The new ideal canopy with 1.2 leaf layers sheltering a reduced crop load wasn’t working quite as smoothly as expected.

In fact, the best fruit harvested from the vines planted in the wake of phylloxera was frequently the most sheltered fruit.

“If you tested and measured the color of it, you’d find the least exposed clusters have the highest amount of color. And when you make wine from them, they make the best wine,” Dokoozlian explained. “It’s not that we had too much light, it’s that by giving the clusters that much light, they get too much sun, and the temperatures increase.”

Some growers even began avoiding fruit on the southern and western sides of the vines because the afternoon sun effectively burnt them. Wines made from the overexposed grapes had a distinct savor of dried fruit rather than the fresh fruit flavors consumers expected.

Growers realized they had to optimize light penetration of the canopy while limiting heat levels, which could be as much as 8 or 9°C higher than on the more sheltered side of the vine.

Dokoozlian said the experiences have shown that canopies must be managed with a view to the direct and indirect effects new practices have on the ripening fruit.

“Canopy management is everything we do in the vineyard,” he said.

“We want as much diffuse light as possible with minimal amounts of direct light.”