Vineyard irrigation is a necessary part of vineyard management in dry wine growing regions where winegrowers completely or partly rely on irrigation water. With irrigation, winegrowers can control vine growth and grape quantity and quality. This is because water availability is a crucial factor affecting plant physiology and the quality of grapes. In dry production areas such as the Mediterranean region, the use of irrigation is thus a fundamental practice which grants the economic sustainability of viticulture.
Vineyard irrigation and climate change
In addition to areas traditionally considered as “dry” during the growing season, new regions are increasingly showing the need of irrigation. The climate change underway is leading to an increase in temperatures and a reduction in rainfall in the summer period, increasing water stress in vineyards, which could potentially undermine both yield and grape quality. These changes will make it necessary to implement irrigation in viticultural areas for which drought is a new phenomenon. The increase in temperatures will also cause a reduction in the water resources available, making it necessary to decrease the water footprint by using deficit irrigation strategies which optimize water use efficiency.
Such practices are already routinely adopted in viticultural areas with limited rainfall throughout the production season. Indeed, irrigating with small amounts of water has the effect of reducing growth and canopy size, limiting transpiration losses and therefore maintaining production and quality at reduced water inputs. However, particular care must be exerted, as the line between moderate and excessive water stress is very thin and crossing it might lead to incomplete/unbalanced ripening and deteriorate the polyphenolic and aromatic profile of wines. For this reason, a deficit irrigation strategy needs to be carefully planned and its effects need to be continuously monitored.
What is deficit irrigation in viticulture
Deficit irrigation maximizes the efficiency of water use, by concentrating limited seasonal water supplies to drought-sensitive crop growth stages. Outside these periods, irrigation is limited or even unnecessary if rainfall provides a minimum supply of water. Water application is therefore inferior to the actual water needed for maximum growth. While this inevitably results in plant drought stress and some production loss, it maximizes productivity for a given amount of water and stabilizes yields.
For grapevine, the effect of water deficit on fruit growth varies according to the period during which it is applied. Research shows that it is greater when it is applied during berry formation (between flowering and veraison) when can limit cell division and expansion and decrease the final size of berries and total yield. Similarly, a stress applied at the time of flower bud differentiation can negatively impact fruitfulness and production the following year.
Fruit quality is also sensitive to water stress, depending on its levels. Whereas moderate stress can increase sugar concentration and anthocyanins and phenol compounds in berries (thereby enhancing wine color and aroma), excessive stress and high temperatures could cause a photosynthetic limitation reducing the accumulation of sugar. Finally, water stress can impact on acid content in grapes in interaction with temperature. This effect is particularly pronounced after veraison, when rapid acid degradation due to high temperatures and water stress can result in dull wines lacking freshness and crispness.
Using Vintel for deficit irrigation: an experimental study during the Italian drought of 2022
It is now clear that under climate change, the key to viticultural sustainability will be the adoption of smarter and more precise water management strategies. For that, it is crucial to have a complete vision of the water status of vineyards and its evolution over the production season. New technologies provide us with different tools that can support informed irrigation choices, and optimize water use during drought. One of these tools is the irrigation DSS Vintel, which uses accurate plant-soil models to simulate vineyard water status, and give irrigation recommendations, day by day according to production objectives.
A recent study by the university of Udine, Italy, has highlighted that Vintel can indeed help plan and optimize irrigation to preserve production and quality in areas hit by summer drought, which is becoming more and more frequent. Vintel has been chosen by the University of Udine within the European project “Aquavitis” as a tool to conduct trials on the effects of water availability and the impacts of climate change on the vineyards of the Friuli Venezia Giulia region, in North-Eastern Italy.
Indeed, in the spring-summer of 2022 Northern Italy has experienced one of the worst droughts in the last 70 years, with precipitations reaching a historical minimum and rivers running almost dry. The drought has resulted in water restrictions and has hit hard the agricultural sector, as low river levels made irrigation difficult.
Paolo Sivilotti, the researcher who supervised the trials explains : ” The test was conducted in 2021 and 2022 near Udine. It analysed the response of Pinot gris, a typical variety from the region, to three different water treatments: no stress, moderately stressed, severely stressed. ” To monitor and maintain these water stress levels over the season, Mr. Sivilotti used Vintel, which simulates predawn water potential as an indicator of plant water status.
Using Vintel, water potential was mantained at:
- No stress : -0.2 MPa over the whole season
- Moderate stress : -0.35 MPa between flowering and harvest
- Severe stress : -055 MPa between flowering and harvest
” What was really interesting was to see whether a deficit irrigation strategy could help optimize water use and what level of stress should be maintained after flowering to ensure a satisfactory yield and grape quality. The DSS Vintel was the ideal tool to conduct this study because its models do not just simulate soil moisture but provide a direct estimate of the effect that soil water shortage has on vine water status. The pressure chamber measures made during the growing seasons confirmed the accuracy of simulations, making any DSS adjustment unnecessary.”
No water stress
Moderate water stress
Severe water stress
The results show that “the moderately stressed regime allowed to save 31% and 50% of irrigation water in 2021 and 2022 with modest impacts on yield and physiology, and without any repercussions on quality“. Indeed, a wine tasting panel has tried the wines produced in 2021, and no difference between the stressed and non-stressed wines has been remarked.
“Obviously more studies are needed to assess the best deficit irrigation strategies in different viticultural contexts.”
However, results confirm that under climate change, precision deficit irrigation can be a valuable strategy preserving production, quality and decreasing the water footprint of viticulture.
“Not only, during extreme events like the one that hit Northern Italy this summer, deficit irrigation might be the only possible alternative, if water restrictions are put in place or if water becomes too expensive.” In this context, tools like Vintel are precious allies to vine growers in the creation a climate resilient, more sustainable viticulture.
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Wine quality depends on the effective management of alcoholic fermentation, which is a key process carried out by the yeast Saccharomyces cerevisiae in the musts. One of the key factors in successful fermentation is the availability of yeast-available nitrogen (YAN). If the musts lack sufficient YAN, fermentation can be delayed or stopped altogether, resulting in the formation of undesirable compounds that alter the wine’s aroma. To avoid these problems, an adequate level of YAN is crucial.
What is YAN ?
To convert grape sugars into alcohol efficiently, yeasts need sufficient quantities of assimilable nitrogen, mainly in the form of ammonium and amino acids… Among amino acids, some, such as proline, are not assimilable by yeast. This is because Saccharomyces cerevisiae, unlike other yeasts, lacks external proteases (enzymes that digest proteins) and therefore cannot hydrolyze peptides and proteins to extract amino acids. Therefore, YAN includes only ammonium ions (NH4+), free amino acids, and some peptides, which means that assimilable nitrogen can represent less than 50% of the total nitrogen.
Nitrogen requirements of yeast during fermentation
Scientific studies show that a YAN level above 180-200 mg/L is optimal for ensuring regular and complete fermentation. Lower levels can lead to incomplete fermentation, leaving residual sugars and producing wines of lower quality. According to the Institut Français de la Vigne et du Vin (IFV), the minimum YAN level in a should be at least 140 mg/L, including 50 mg/L in the form of ammonia, toto prevent fermentation from stalling.
Furthermore, YAN also influences the aromatic profile of the wine. The production of aromatic compounds, particularly esters, largely depends on the amount of assimilable nitrogen available to the yeast. Generally, the initial concentration of assimilable nitrogen in the must is directly related to the quantity of aromatic compounds produced during alcoholic fermentation
Nitrogen fertilisation to improve must quality
YAN level is therefore a key indicator for winegrowers seeking to optimise the quality of their musts. Proper nitrogen fertilisation increases the nitrogen content of the berries. For example, trials carried out by the IFV between 2005 and 2009 showed that urea-based foliar fertilisation can boost the nitrogen content of berries by 50% to 100%, depending on the dose applied.
If musts are low in nitrogen, adding YAN as a nutrient during fermentation is an option. However, this method can result in different aromatic profiles compared to wines from vineyards with adequate nitrogen fertilization.
For example, a recent study on Chardonnay revealed that, while adding nitrogen in the form of diammonium phosphate or organic nitrogen during fermentation can achieve fermentation kinetics similar to those from vineyard fertilization, they produce wines with less pronounced tropical fruit aromas.
In summary, while cellar additions of nitrogen are effective for completing fermentation, conducting a balanced fertilization in the vineyard is preferred as it enhances the aromatic characteristics of the wine.
Using decision-support tools to control nitrogen nutrition
Decision-aid tools such as Vintel® are particularly useful for improving nitrogen nutrition in vineyards and, consequently, the fermentation process. These tools enable winegrowers to forecast the nitrogen requirements of their vines based on environmental conditions (soil, weather, cover crops) and the specific characteristics of plants (phenological stage, growth, target yield). Thanks to this data, winegrowers can fine-tune their fertilisation practices, optimising nitrogen uptake and, ultimately, the quality of their musts, ensuring that they ferment evenly to produce quality wines.
In short, precise fertilisation adapted to each vineyard is essential for producing high quality grapes and ensuring optimal fermentation. Effective management of assimilable nitrogen helps to prevent fermentation issues and produce top wines.
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Summer brings new challenges for vineyards, with the appearance of various pathogens. While downy mildew is a concern in spring due to frequent rainfall, summer sees the prevalence of other harmful diseases that can impact on grape quality.
What diseases commonly affect vines in summer?
Oidium and Black Rot are two pathogens that can seriously affect leaves and bunches during growth and veraison. Powdery mildew, in particular, does not require rain or leaf wetness to develop, making it a threat even in summer, which is generally a less rainy period.Black Rot, on the other hand, poses the greatest threat to vines during the critical phenological phase between the fall of the flower caps and veraison.
Post-veraison, grey rot, or botrytis, is particularly problematic. This fungus feeds on the sugars contained in the berries, damaging the bunches and encouraging the development of acid rot. It also imparts unpleasant odours and flavours to the wines produced.
Major consequences for vineyard health and wine quality
The impact of these diseases on vineyard health can be devastating, reducing both yield and quality of the harvest. Grapes affected by these pathogens often lead to wines with undesirable aromas and tastes, far from the desired quality level.
Prevention : an effective strategy
Proactive control and prevention strategies are essential to protect vineyards from these summer diseases.
Vineyard maintenance for optimum management
It is important to select resistant grape varieties and prune properly to improve air circulation and reduce humidity, which limits the development of pathogens. Frequent inspection of the vines allows early detection of the first signs of disease. It is crucial to intervene immediately when symptoms appear to prevent the spread of disease.
The application of specific fungicides and biocontrol products, such as plant extracts or antagonistic micro-organisms, must be carried out in accordance with recommended treatment schedules or the predictions of disease DSTs (Decision Support Tools).
In the case of a plot sensitive to black rot, it is useful to use anti-mildew or anti-oidium products that also have an anti-black rot action to have a comprehensive defense strategy.
Vigilance for high-performance vineyards
Even in the drier summer months, we must not lower our guard. Vigilance and early intervention are crucial to maintaining healthy vineyards and guaranteeing high-quality wine production. Decision support systems (DSS), such as Vintel®, provide precise alerts on disease pressures. This enables winegrowers to optimise treatment timings and implement effective preventive measures, thereby enhancing vine protection and securing the future harvest against summer diseases.
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This year 2024, French vineyards are experiencing an unprecedented level of powdery mildew pressure. Vines were hit by early contaminations starting in late March, owing to early phenology and mild, wet weather. Such an early onset of attack is exceptional in this regionWeather conditions in April and May, marked by heavy rainfall, exacerbated the situation, making disease management particularly difficult. While some regions are beginning to benefit from drier weather, allowing better control of the disease, the importance of vigilance and effective application of treatments remains crucial to limit damages.
Downy mildew, a significant impact on plants and yields
Downy mildew, caused by the pathogen Plasmopara viticola, attacks various parts of the vine: leaves, bunches and berries. This disease has several negative effects:
It reduces the leaf surface used for photosynthesis. Affected leaves exhibit oily yellow spots on their upper surface and white mold on their underside.
It damages the berries turning them brown and crushed, consequently decreasing the quality and yield of the harvest.
It weakens the shoots, preventing shoot development and wood formation, making winter pruning more difficult. These combined effects reduce the vine’s reserves, compromise berry growth and make the plants more vulnerable.
What conditions are conducive to risk?
The development of downy mildew is favoured by specific climatic conditions:
Ideal temperatures for the spread of the disease are between 20 and 25°C with a humidity level of 85% or more.
Prolonged rainfall, dew and morning fog exacerbate the risk of contamination.
Periods of vigorous vine growth, when new shoots are most vulnerable, are particularly critical. In addition, certain grape varieties, such as Cabernet Franc, Cabernet Sauvignon, Chardonnay and Merlot, are particularly sensitive to mildew.
Appropriate treatment and prevention methods
Copper-based fungicides and specific systemic products are commonly used to combat downy mildew. It is essential to alternate the types of fungicide used to prevent the pathogen from developing resistance. In addition, combining substances with different modes of action and creating spatial heterogeneity in their application helps to prevent the development of pathogen resistance.
Various cultivation techniques can prevent downy mildew, such as pruning to improve air circulation around the plants, removing infected debris to reduce sources of contamination, and ensuring effective drainage to avoid puddle formation. Green pruning eliminates unnecessary shoots and promotes shoot aeration; maintaining a cover crop protects the soil and reduces water or contaminated soil splashes. Trellising and leaf removal also improve aeration. Finally, controlling plant vigour by limiting fertilization prevents excessive growth, which is conducive to powdery mildew.
Protecting vines effictively
For an effective protection against downy mildew, it is essential to follow reliable weather forecasts when planning treatments, to avoid water stagnation around the plants, and, in years with high disease pressure, to ensure a continuous phytosanitary protection without excessively long intervals between treatments. It is also important to regularly check the functionality and efficiency of sprayers, and to use decision-support systems such as Vintel to receive risk alerts on downy mildew and other diseases
Proactive, well-informed management is key to effective powdery mildew control. By combining different strategies, winegrowers can protect their vines and ensure the quality of their harvest inspite of the challenges posed by the unfavourable climate conditions of 2024.
