Nicolas Cantacuzene,
Emeritus Vineyards, Sebastopol, CA

Leaf removal is a widely used practice in California to fight disease pressure and influence wine quality. While it is agreed that leaf removal is beneficial, in California excessive removal (known as “over-leafing”) could affect grape quality. Pinot Noir, though not as photo sensitive as Sangiovese and Grenache, is thin-skinned and is therefore more prone to sunburn, disease, and temperature increase.

Winegrowers have practiced leaf removal to influence different wine styles and allow air circulation to fight disease pressure.

Since Sunlight into Wine by Richard Smart and Mike Robinson was published, winegrowers have been favoring more fruit exposure, but at what cost? A recent article written by Mark Greenspan (Advanced Viticulture, Santa Rosa, CA) has underlined the excessive practice of leaf removal and its impact.

The object of this article is to survey a number of wineries to determine what methods and motives are behind leaf removal in high quality Pinot Noir production in California.

Among the people surveyed, most winegrowers appear to practice leaf removal to some degree. Two schools of thought emerge from this survey — growers who carry out leaf removal to varying degrees and growers who favor shoot thinning and lateral removal.

It appears that over-leafing was more predominant a few years ago, as Michael Browne (Kosta Browne, Sebastopol, CA) notes: “A few years ago many of our growers were stripping the fruit zone because that was what everyone was doing.”

However, recently there has been a tendency among most growers to refrain from fully exposing the fruit zone. They have observed that stripping the fruit zone could negatively influence grape quality: “If high heat occurred, as it often does, the clusters would dehydrate quickly and also get bleached by the sun,” adds Browne.

The main reasons behind leaf removal for most growers are combating disease by allowing more air flow, favoring skin thickening, and influencing wine style. However, there are a range of options pertaining to the quantity of leaves to be removed or retained without damaging the grapes or the vine.

A typical program for growers is to practice leaf removal (also known as “leafing”) on basal leaves at fruit set or thereafter, and not on the afternoon side, unless it is a high disease pressure year. Removing leaves at fruit set allows the fruit to acclimate to a certain amount of sun exposure and promotes bud fruitfulness for next year’s crop.

Browne is experimenting with leafing pre-bloom on basal leaves in order to encourage next year’s bud fruitfulness, promote light into the canopy earlier, and facilitate operations for his crew before the canopy grows too large.

Browne observes that early leafing produces “a bit of shatter and a more open cluster which we like. The remaining leaves tend to grow down and protect the fruit zone also.” However, he notes that the clusters are not protected, which could be troublesome if there is rain or wind at bloom.

More traditional leaf-removal programs promote leafing at fruit set. The extent to which leaves are removed varies among growers. Marty Hedlund (Dehlinger Winery, Sebastopol, CA) says, “We shoot-thin, shoot-position, remove leaves and laterals, cluster-thin, and cool the fruit zone with sprinklers (if necessary). Fruit/wine quality and plant health are the reasons for incorporating these operations into our efforts. The degree to which we use any, some, or all of the above is dependent upon the wine, variety, and site.”

Scott Zapotocky (Paul Hobbs Wines, Sebastopol, CA) says, “We leaf approximately half the basal leaves on the eastern side of the vines to increase air flow and filter sunlight to the clusters. We do this in late May/early June, or once vine growth slows down.”

One advantage of leaf removal is a thickening of the skin, and better air circulation that allows for fewer incidences of disease. Ginny Lambrix (DeLoach Vineyards, Santa Rosa, CA), who manages many vineyards in the Russian River Valley and on the coast, evaluates her need for leafing at fruit set on a case-by-case basis.

“The light environment is one of the factors I consider,” says Lambrix. “If the vineyard is organic, in a high fungal pressure area, prone to tough tannins or low color, or has produced vegetal wine, then we pull basal leaves. If the vineyard is weaker, thus smaller leaves and better light, I am less inclined to pull leaves, but shoots have to be positioned and C-clipped to retain air flow and the light environment. I never pull leaves late.”

Kirk Lokka (Emeritus Vineyards, Sebastopol, CA), notes that sun exposure produces softer tannins and gives the perception of early maturity. “Leaf removal is necessary in the Russian River Valley due to the fog influence,” adds Lokka.

Steve Dooley (Stephen Ross Wines, San Luis Obispo, CA), who grows grapes in the cool climate of the Central Coast, believes, “Sunlight on grapes makes dark, flavorful wines with polymerized tannins.”

Some winery clients of Jeff Newton (Coastal Vineyard Care Associates, Santa Ynez, CA), who manages vineyards in Santa Barbara County, prefer full sunlight as a way of advancing stem maturity. “Their style of winemaking,” he says, “includes extensive stem inclusion and they need those stems to be as mature as possible.” This extreme leafing technique requires cool summer conditions in order to avoid sunburn.

Dean de Korth (Bernardus Winery, Carmel, CA), who practices leaf removal to some degree in Carmel Valley, encourages filtered light and tries to “avoid sunburn at all cost. If heat is eminent, leafing might be postponed.”

Depending on weather conditions, proponents of leaf removal will adapt their regime. Mark Bixler (Kistler Vineyards, Sebastopol, CA), says, “Since we are in the Russian River Valley with all its June/July/August morning fogs and the risk of botrytis is high, if it rains in the last few weeks before harvest, we then pull leaves on the afternoon sun side of the vines to allow quick drying of the bunches (not really with the objective of allowing more sun exposure).”

Dr. Bob Wample (Cal State University, Fresno), notes that, in his opinion, people should be cautious about which leaves they decide to remove. “In most situations I would restrict leaf removal to those leaves positioned at or below the cluster on the shoot since those above the shoot are the primary source of carbohydrates for the developing cluster. More leaves on non-bearing shoots can be removed to improve light penetration and reduce the potential for powdery mildew infection if desired.”

Some growers have been producing high-quality fruit by shoot thinning and lateral management. Many winegrowers who practice minimal leafing believe appropriate canopy management is adequate to bring the fruit to maturity without mildew incidence and loss of varietal character. The belief is that shoot thinning gives an adequate amount of filtered light to the clusters and promotes even ripeness of the fruit without substantial fluctuations in temperature.

Daniel Roberts (Integrated Winegrowing, Sebastopol, CA), who advises a number of growers in cool climates, notes that, “Grapes on leafed clusters are five to ten degrees warmer in afternoon sun depending on row direction.”

Roberts does not believe in leaf removal as a general rule and uses shoot thinning as a means of managing the canopy. He advises his clients to cane-prune, shoot-thin to three shoots per foot, position shoots with branch locks, and also remove laterals in the fruit zone, one node above the top cluster, morning side only. Roberts considers shoot thinning and lateral removal appropriate for combating disease. Roberts says, “These techniques lost less than 1% of the Pinot Noir or Chardonnay to botytris.”

Other growers also believe leaf removal is not suitable for their program and prefer focusing on canopy management. Doug Braun (Presidio Winery, Santa Ynez, CA) in the Central Coast region believes in lateral removal and acknowledges that leaf removal is beneficial in combating disease. He believes filtered light is appropriate and that leaf removal does not “move varietal character in the right direction or help grape maturity.”

Randy Heinzen (Director of Viticulture, Saintsbury, Napa, CA), who practices leaf removal, considers the management of laterals a very important tool. “If managed properly, laterals or lack of laterals,” says Heinzen, “can drive late season ripening and be responsible for protection against sunburn.”

Proponents of shoot thinning believe that this technique provides an appropriate amount of sunlight to fruit and promotes even ripeness. Some growers, observing the increase in leaf removal stimulated by Smart and Robinson, have re-evaluated their practices and have favored shoot thinning over leafing. Most of the methods proposed by Dr. Smart for leafing are adapted to more vigorous sites. For most of the proponents of shoot thinning, filtered light is adequate to carry berry ripening and sugar accumulation while maintaining varietal character, without a high incidence of mildew.

Many people interviewed believe filtered or dappled light is preferable to direct sunlight. However, there seems to be a wide variety of options concerning the amount of light to which the clusters are exposed. Too much fruit exposure will burn the fruit, whereas too little will influence development of green characters.

Depending on the region and style of winemaking, growers will either shoot-thin or remove leaves as a function of the style of winemaking. Roberts does mostly shoot thinning in cool regions.

Fred Scherrer (Scherrer Winery, Sebastopol, CA), observes, “I think sun exposure has more to do with fruit personality than with speed of ripening. Excessive exposure can lead to too many base notes and tannin, not enough perfumes and grace.”

Newton notes that high-quality grapes can be grown under a wide variety of canopy management scenarios in the Santa Ynez Valley. Some clients ask Newton for maximum leaf removal, and others simply trim laterals, retaining two or three basal leaves. From his observations, he believes leaf removal is mainly a function of wine style. “Not leafing can result in slight vegetal flavors while overexposure can reduce fruit flavors in the wine,” says Newton.

Anytime leaves are removed, it will increase berry temperature. Some regions might require an increased berry temperature, whereas other regions will require that it be lower. Temperature and not light incidence was found to have a detrimental effect, increasing the accumulation of anthocyanin. Studies conducted by Nick Dokoolizian et al. suggest that the beneficial effects of light decreased with elevated fruit temperature.

Mark Greenspan, says: “Higher fruit temperature will have little effect on sugar accumulation, but will increase the rate of berry metabolism.” Sunlight is indeed needed to fully develop fruit composition. However, if the fruit temperature is elevated (about 85ºF), there is a decrease in color and phenolic development, and also a higher pH and lower titratable acidity.

Proponents of shoot thinning believe there is a balance between sugar accumulation and berry metabolism. If the berry temperature is too high, berry metabolism will occur at a different rate than sugar accumulation. In choosing a canopy management program, it is important to consider the balance between sugar accumulation and berry development. Ideally, these processes should evolve in conjunction. Heinzen notes that “proper leafing helps define the rates of sugar maturation versus phenolic maturation.”

Canopies should be managed with the intention of balancing the vine. There are as many possibilities of leafing/thinning as there are wine styles. Either extreme leafing or lack of it have detrimental consequences for grape/wine quality.