Canopy management is something that most wine drinkers never think about. However, it is critical to fruit quality. Through canopy management, vineyard managers arrange the green shoots of the vine on the trellis and manage the leaf area throughout the season. In regions that represent climatic extremes, such as California’s Napa Valley and New York’s Finger Lakes, vineyard managers will make very different canopy management decisions as they consider factors such as sun exposure, air flow, temperature, and mechanization.
To understand the challenges of vineyard management in Napa and the Finger Lakes, it is first essential to understand their climates. Napa has a Mediterranean climate. This means it has a wet season in the winter and a dry season in the summer. This type of climate can also have wide diurnal swings (the difference between the high and low temperatures during a 24-hour period); however, the ranges of yearly highs and lows are less extreme than in other climates. The humidity is low during the dry season, and the intensity of the sun is quite strong. In contrast, New York’s Finger Lakes region has a continental climate, with pronounced seasonality and precipitation of various forms throughout the year, including rain, ice, and snow. During the spring and summer, humidity is high. This area is more northerly in latitude, which extends the sunshine hours during the summer as late as 9pm, but this also leads to an exceedingly early sunset around 4pm during the winter. The diurnal swings are less pronounced than in the Mediterranean climate of Napa, but the high and low temperatures of the calendar year are dramatic. It is because of these differences between the two regions that their considerations for canopy management diverge.
When discussing canopy management, it is also important to understand the goal of the vine. In the wild, grapevines climb trees. The host tree forms the structure on which the vine can grow and ultimately reach a sunny spot high in the tree’s canopy. The relationship between the vine and the host tree is mildly competitive, not for water or nutrients but for sunlight. Until the vine reaches sun, it primarily focuses on vegetative growth, sending shoots upward in search of a spot in the light. Canopy management decisions must take these natural tendencies of the vine into account.
Because sun exposure is critical to the fruit initiation process, it is clear why it would be of interest to a vineyard manager. However, fruit initiation is only one part of sun exposure. Photosynthesis, the process by which plants make their carbohydrates for food, needs sunlight to take place. The way the leaves are arranged on the trellis is critical to optimizing exposure to direct sunlight. In fact, a leaf will absorb approximately 90% of the sun’s energy that reaches it. This means that if a leaf is second in line, shaded by other leaves on the vine, it will only receive about 10% of the sun’s energy to convert into sugar. The leaf will receive just 1% if there are two leaves in front of it. In an area with a long growing season, such as Napa, this is not as critical. However, in the case of the Finger Lakes, every hour of sunlight is precious. The short growing season is already a challenge, but add in cloudy or rainy days with little photosynthetic energy available, and a vineyard manager must work to optimize the photosynthetic ability of each leaf.
Hans Walter-Peterson, viticulture extension specialist at Cornell, says, “We get rains and more humid conditions during the growing season, and VSP [vertical shoot positioning] and Scott Henry training help to better expose leaves and fruit to air movement and sun to allow them to dry more quickly, which reduces disease pressure.” This can also be done through a trellis organization known as the Lyre method, which is how my family’s Finger Lakes winery, Trestle Thirty One, plans to train our future vineyard. This training method splits the canopy into a v-shape and allows light to infiltrate down into the middle of the canopy and to the outside. While VSP trellis systems are most common, a Lyre or modified Lyre allows for more sun exposure on all the leaves of the canopy.
In Napa, many of the training systems are similar, with the exception of head-training, which is risky in more humid environments. The VSP systems are modified to allow for what is called California Sprawl on the afternoon side (the side that gets direct sunlight in the afternoon), which helps protect the fruit from the sun.
Sun exposure also plays an important role in flavor development. This is why training systems such as the pergola method are not ideal for wine grapes. The pergola maximizes sun exposure for leaves but largely shades the fruit. Sun exposure on developing grape skins aids in the production of flavanols, which enhances wine quality. However, too much of a good thing can be a problem. In Napa, so-called dappled sunlight is preferred, because full exposure to intense sunlight can cause sunburn of the fruit, which inhibits anthocyanin formation and can cause the berries to take on a “cooked” character. This dappled light effect is achieved by careful leaf pulling, or the removal of leaves in and occasionally above the fruiting zone, so that the fruit is not overly exposed to the sun. In the Finger Lakes, since the sun is less intense and more precious, growers can expose more of the fruit to direct sun by pulling more leaves, particularly on the morning side of the row.
Airflow is also a particularly important consideration for vineyard managers. A canopy that has ideal airflow is referred to as an “open” canopy and typically has dappled sunlight throughout the leaf zone and no tightly packed shoots. In mid-summer, having good airflow through the canopy and around the fruit can help mitigate disease pressure. In Napa, because of the low humidity, this is usually not a problem. However, in wet springs, such as that of 2019, having an open canopy helps control fungal diseases like powdery mildew. Open canopies also help with spray penetration when a grower needs to address a disease issue before it becomes problematic. “Proactive prevention is key and having an open canopy is critical for that, particularly when dealing with powdery [mildew],” says Matt Allenson, vineyard manager for Foley Family Wines in Carneros.
In the Finger Lakes, fungal disease pressure exists throughout the growing season because of the high humidity, and constant new growth due to year-round rain creates susceptible tissues for mildew. Therefore, in the Finger Lakes, constant canopy management to create airflow is very important, while in Napa, canopy management is generally a once-per-season practice.
The temperature of the canopy is key to the health of the vine. Vines transpire, and through this process, the microclimate within the canopy is kept slightly cooler than the air in the mesoclimate of the vineyard. If the temperature of the canopy becomes too hot, generally around 96 degrees Fahrenheit, the vines will shut down and cease both transpiration and photosynthesis. This can happen during a heat spike, periods of water stress, wind events, or some combination of these. This is particularly important in Napa, where irrigation is widely used to supplement what little groundwater the vines can find during the heat of the summer and early fall. Growers pay close attention to both vineyard and canopy temperature to monitor how the vines are coping with the weather.
Lastly, when considering different methods of canopy management, the practical aspect of farming needs to be examined. Mechanization can have profound impacts on how a canopy can be managed. For example, if vines are head trained, as is the case with the iconic I-Block Sauvignon Blanc at Robert Mondavi Winery, mechanization will be limited, and labor will need to be sourced for nearly all tasks. On the opposite end of the spectrum, if a manager wishes to fully mechanize, using a VSP system is ideal. The canopy is neatly controlled, and if shoot positioning is done using a skilled crew, most other jobs in the vineyard can be done largely by machine, with a small amount of hand follow up if needed. Finding skilled vineyard labor is a problem in both Napa and the Finger Lakes, and demand is high for the crews that are available in these regions.
The general principles of canopy management are the same throughout the world. Sun exposure on leaves and fruit must be optimized by managing the leaf area of the vines. Airflow must be monitored to assist in reduction of fungal disease pressures and with spray penetration. Canopy temperatures are an important indicator of vine stress, and the costs of canopy management must be taken into account. Even so, regional challenges require different approaches. Napa and the Finger Lakes are two extremes, but there are unique conditions in all wine-growing regions. The dexterity required of vineyard managers is what makes growing in different areas of the world exciting and unique.
Excellent essay, Nova!
Thank you for sharing, great article! Just a quick question: why do you say that pergola is not an ideal system? Winemakers in Rias Baixas have been successfully managing disease pressure by using the pergola system. Or VSP would be better, but they do it because of tradition?