Fungus-resistant grape cultivars, commonly referred to as PIWIs (an abbreviation of the German term pilzwiderstandsfähig), are hybrids of Vitis vinifera with other Vitis species that exhibit low susceptibility to powdery mildew (Erysiphe necator) and downy mildew (Plasmopara viticola), the major fungal diseases in viticulture. In contrast, traditional grape cultivars are highly susceptible and require frequent fungicide applications during the growing season. The reduced number of fungicide treatments required by PIWIs lead to significant environmental and economic advantages, including fewer tractor passes, lower fuel and water consumption, and reduced pesticide-related waste. However, these benefits are rarely quantified.This study compares two fungus-resistant cultivars (Cabaret noir and Sauvignac) with two traditional ones (Pinot noir and Rivaner), using data from an experimental vineyard in Luxembourg. Environmental impacts are assessed using Life Cycle Assessment (LCA), and economic costs analysed both from a private and social perspective, accounting for direct production costs and environmental externalities.Results show that fungus-resistant cultivars can reduce environmental impacts by up to a factor of three, particularly in the climate change and freshwater ecotoxicity categories. Economically, growing PIWI cultivars allowed average savings of €685/ha/year at the level of the winery (mostly driven by lower fungicides use) compared to traditional cultivars. The estimated environmental costs in PIWI systems were €157/ha, compared to €406/ha for traditional systems. Sensitivity analyses confirmed the robustness of these findings across variations in disease pressure, yield and input prices, while showing that additional fertilizer inputs can reduce the relative magnitude of the environmental advantage.Altogether, the findings highlight the strong potential of fungus-resistant cultivars to lower both the environmental and economic burden of viticulture, supporting their broader adoption as a sustainable alternative.

Due to their high potential for fungicide reduction, fungus-tolerant “PIWI” cultivars are increasingly gaining interest in European viticulture. This investigation aimed (i) to obtain phenological observation datasets of PIWI cultivars across a broad set of European locations, (ii) to apply the temperature sum based “UniPhen” model allowing for a precise simulation of the phenological development at all BCCH stages between bud swelling and berries ripe for harvest and (iii) to discuss the potential implementations in applied viticulture as well as in viticultural climate change impact research. Four consecutive years of complete data sets of phenological observations originating from eight locations in Central Europe for 13 PIWI and 3 traditional cultivars were used to apply the UniPhen model using a cumulative degree day approach with three temperature thresholds (lower threshold: 10 °C; upper threshold: 20 °C; heat threshold: 30 °C). Muscaris showed the thermal-temporally earliest budburst, while Solaris was earliest in beginning of flowering and harvest ripeness. The latest budburst and the latest beginning of flowering in PIWI cultivars were observed in Pinotin, while harvest ripeness was reached latest by Calardis blanc. The average normalised standard deviation (SD15 °C) over all stages, locations and cultivars was 5.5, corresponding to 5.5 days at 15 °C, with the lowest SD15 °C values around budburst and flowering stages. The highest SD15 °C values were observed in the bunch closure and post-veraison stages. UniPhen “PIWI” enables a precise simulation of all 31 BBCH stages between the beginning of the bud swell (01) and berries being ripe for harvest (89) for 13 fungus-tolerant cultivars and can be extended to additional cultivars. The model can be applied (i) as a bioclimatic indicator describing the suitability of a location/region for the cultivation of specific cultivars under present and future climate conditions, (ii) for the simulation of cultivar-specific phases of highest susceptibility for fungal diseases and, indirectly, the timing of fungicide treatments as well as (iii) for the classification of the relative late frost risk depending on the thermal-temporal precocity of budburst. This knowledge helps to lower the barrier to growing PIWI cultivars and helps to pave the way for a more sustainable, climate change-resilient viticulture.

Budbreak plays an important role in the grapevine growing cycle and temperature is its main driver. Therefore, phenological models use two temperature-based approaches to simulate budbreak: a chilling-forcing scheme, which describes either endo- and eco-dormancy periods, or a forcing-approach, which exclusively simulates the eco-dormancy period. Both approaches are able to estimate budbreak under current temperature conditions, but they diverge under future climate forecasts. Additional divergences in phenological estimation are driven by climate as simulated by different global and regional circulation models and GHG concentration scenarios. Thus, this study explored the sources of uncertainty in budbreak estimation across Europe in a historical baseline (1976-2005) and near-future (2026-2055) climate. The experimental design comprised six phenological models calibrated for eight distinct grapevine varieties. These phenological models were applied to one historical and two future representative concentration pathways using different combinations of regional and global climate models according to data availability. In total, 25 experiments were performed for the historical period and 35 for the near-term future (18 and 17 for RCP2.6 and RCP4.5 scenarios respectively). The results showed different spatial domains of uncertainty across Europe. The total uncertainty in estimating budbreak was low in Central Europe and increased outside these regions in both the historical and future periods. Specifically, the uncertainty in the baseline period was mainly related to the phenological models (~94.7 %) with slight spatial differences across the study area. In the future period, Central Europe was characterised by high uncertainties due to the climate models (~40 %). Outside these regions, uncertainty increased due to the phenological models, the highest uncertainties being associated with the Mediterranean basin for the cold-adapted varieties, while the north/northeast regions showed the highest uncertainties for the warm-adapted varieties. High temperatures resulted in low daily chilling rates for BRIN, while only certain temperatures positively contributed for UNIFIED and UNICHILL. Additionally, low temperatures did not accumulate forcing units for any phenological model, while an increase in temperature led to a linear (GDD, Richardson-BRIN until a threshold) or parabolic (WANG, UNIFORC) increase in the daily forcing unit rate. These differences limit the use of the phenological models, which will need to be taken into account when applying these models in their application in different environments in the future.

Sunburn on grapes has emerged as an economic concern in recent decades. The phenomenon can be attributed to climatic changes, characterised by elevated air temperatures and intense solar radiation, leading to increased crop failures as well as quality losses of wines. This study aimed to evaluate comprehensively selected preventive strategies for the sunburn-sensitive, white cultivar ‘Riesling’. To this end, the impact of the timing of bunch zone defoliation on sunburn necrosis within three wine-growing regions in Central Europe, as well as the application of sunscreens onto grapes and shading by protective nets at one of these sites, were visually assessed in the contrasting growing seasons 2021 and 2022, respectively. Early defoliation between the end of flowering and fruit set decreased sunburn necrosis severity by down to 59.6 % in comparison to late defoliation at bunch closure across the two years. Furthermore, rot severity was reduced by down to 85.3 % in comparison to no defoliation across both growing seasons. The application of lime onto grapes following late defoliation diminished sunburn damage by 41.9 % across both experimental years, while kaolin showed no effect. Combining early defoliation with application of lime revealed an increased effectiveness of 79.2 % in comparison to late defoliation within one growing season. Different protective nets were able to lower sunburn damage within each growing season, but the black, small-meshed shading net with the highest shading factor investigated revealed the highest effectiveness of 63.7 % across both experimental years. However, the effectiveness of defoliation, sunscreens and protective nets depended on the meteorological conditions during each growing season. Total yield, including grapes with different levels of damage, as well as the vigour of vines, were not impacted by the viticultural measures. Malic acid and total acidity concentrations in the must were decreased by early defoliation compared to no defoliation within each year, while must weight was not influenced by any measure. In conclusion, this study compared the potential of different prevention strategies and highlighted a combined positive effect of early defoliation at two experimental sites and within each growing season: Both sunburn necrosis and rot severity were reduced in comparison to the respective maximum extent.

The Côa region in inner-northern Portugal heavily relies on viticulture, which is a cornerstone of its economy and cultural identity. Understanding the intricate relationship between climatic variables and wine production (WP) is crucial for adapting management practices to changing climatic conditions. This study employs machine learning (ML), specifically random forest (RF) regression, to predict grapevine yields in the Côa region using high-resolution climate data for 2004–2020. SHAP (SHapley Additive exPlanations) values are used to potentially explain the non-linear relationships between climatic factors and WP. The results reveal a complex interplay between predictors and WP, with precipitation emerging as a key determinant. Higher precipitation levels in April positively impact WP by replenishing soil moisture ahead of flowering, while elevated precipitation and humidity levels in August have a negative effect, possibly due to late-season heavy rainfall damaging grapes or creating more favorable conditions for fungal pathogens. Moreover, warmer temperatures during the growing season and adequate solar radiation in winter months favor higher WP. However, excessive radiation during advanced growth stages can lead to negative effects, such as sunburn. This study underscores the importance of tailoring viticultural strategies to local climatic conditions and employing advanced analytical techniques such as SHAP values to interpret ML model predictions effectively. Furthermore, the research highlights the potential of ML models in climate change risk reduction associated with viticulture, specifically WP. By leveraging insights from ML and interpretability techniques, policymakers and stakeholders can develop adaptive strategies to safeguard viticultural livelihoods and stable WP in a changing climate, particularly in regions with a rich agrarian heritage, such as the Côa region.

This study provides the first documented discovery of symptoms caused by the cicada Stictocephala bisonia (buffalo treehopper) in Luxembourgish viticulture. Symptoms were found in 2022 in red grapevine cultivars, also in 2023 symptoms on vine plants occurred and two adults of the buffalo treehopper were caught. A characterisation of the resulting symptoms and a discussion on the species’ potential pest status depending on annual meteorological conditions are provided.

Bunch rot caused by Botrytis cinerea is a major fungal disease in grapevines. Under humid climatic conditions, bunch rot development on grapes cannot be completely suppressed and bunch rot control strategies mainly aim to delay the epidemic. In the present study, we investigated the potential of the innovative cultural practice “partial double-pruning after bloom (PDP)” to delay the bunch rot epidemic on Pinot gris and Riesling cultivars over five consecutive seasons (2016-2020) in Remich/Luxembourg. Control vines were pruned at winter to one 10-node fruiting cane per vine, while in PDP, two 10-node fruiting canes per vine were kept; one of the two canes was removed at BBCH 73 (2-3 weeks after bloom). In all the 10 cultivar*year combinations, the bunch rot disease severity at the final assessment date (shortly before harvest) was lower in PDP than in the control. This reduction was significant (P £ 0.05) in 7 of the 10 cultivar*year combinations. PDP significantly delayed the date when 5 % disease severity was reached; in data pooled over the five years this delay ranged between 10.3 (Pinot gris) and 8.3 days (Riesling). The proportion of non-marketable fruit was significantly reduced by 41 % (Pinot gris) and 53 % (Riesling). Total yield per plant was reduced by 10 % (Pinot gris) and 19 % (Riesling), with a significant increase in total soluble solids at harvest in the case of Riesling. An additional evaluation in the year 2020 revealed reduced cluster compactness in PDP for both cultivars. PDP turned out to be an innovative, efficient, reliable and relatively cost-efficient cultural practice to delay the bunch rot epidemic in grapes. It can be integrated as one module into the best practice strategy to control bunch rot and contributes to pesticide reduction in viticulture.

Most European vineyards are managed under rainfed conditions, where seasonal water deficit has become increasingly important. The flowering-veraison phenophase represents an important period for vine response to water stress, which is seldomly thoroughly evaluated. Therefore, we aim to quantify the flowering-veraison water stress levels using Crop Water Stress Indicator (CWSI) over 1986–2015 for important European wine regions and to assess the respective potential Yield Lose Rate (YLR). Additionally, we also investigate whether an advanced flowering-veraison phase may help to alleviate the water stress with improved yield. A process-based grapevine model STICS is employed, which has been extensively calibrated for flowering and veraison stages using observed data at 38 locations with 10 different grapevine varieties. Subsequently, the model is being implemented at the regional level, considering site-specific calibration results and gridded climate and soil datasets. The findings suggest wine regions with stronger flowering-veraison CWSI tend to have higher potential YLR. However, contrasting patterns are found between wine regions in France-Germany-Luxembourg and Italy-Portugal-Spain. The former tends to have slight-to-moderate drought conditions (CWSI<0.5) and a negligible-to-moderate YLR (<30%), whereas the latter possesses severe-to-extreme CWSI (>0.5) and substantial YLR (>40%). Wine regions prone to a high drought risk (CWSI>0.75) are also identified, which are concentrated in southern Mediterranean Europe. An advanced flowering-veraison phase may have benefited from cooler temperatures and a higher fraction of spring precipitation in wine regions of Italy-Portugal-Spain, resulting in alleviated CWSI and moderate reductions of YLR. For those of France-Germany-Luxembourg, this can have reduced flowering-veraison precipitation, but prevalent alleviations of YLR are also found, possibly because of shifted phase towards a cooler growing season with reduced evaporative demands. Overall, such a retrospective analysis might provide new insights towards better management of seasonal water deficit for conventionally vulnerable Mediterranean wine regions, but also relatively cooler and wetter Central European regions. Acknowledgements: This study was funded by the Clim4Vitis project—“Climate change impact mitigation for European viticulture: knowledge transfer for an integrated approach”, funded by the European Union’s Horizon 2020 Research and Innovation Programme, under grant agreement no. 810176; it was also supported by FCT—Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020.

With global warming, grapevine is expected to be increasingly exposed to water deficits occurring at various development stages. In this study, we aimed to investigate the potential impacts of projected climate change on water deficits from the flowering to veraison period for two main white wine cultivars (Riesling and Müller-Thurgau) in Germany. A process-based soil-crop model adapted for grapevine was utilized to simulate the flowering-veraison crop water stress indicator (CWSI) of these two varieties between 1976–2005 (baseline) and 2041–2070 (future period) based on a suite of bias-adjusted regional climate model (RCM) simulations under RCP4.5 and RCP8.5. Our evaluation indicates that the model can capture the early-ripening (Müller-Thurgau) and late-ripening (Riesling) traits, with a mean bias of prediction of ≤2 days and a well-reproduced inter-annual variability for more than 60 years. Under climate projections, the flowering stage is advanced by 10–20 days (higher in RCP8.5) between the two varieties, whereas a slightly stronger advancement is found for Müller-Thurgau than for Riesling for the veraison stage. As a result, the flowering-veraison phenophase is mostly shortened for Müller-Thurgau, whereas it is extended by up to two weeks for Riesling in cool and high-elevation areas. The length of phenophase plays an important role in projected changes of flowering-veraison mean temperature and precipitation. The late-ripening trait of Riesling makes it more exposed to increased summer temperature (mainly in August), resulting in a higher mean temperature increase for Riesling (1.5–2.5 °C) than for Müller-Thurgau (1–2 °C). As a result, an overall increased CWSI by up to 15% (ensemble median) is obtained for both varieties, whereas the upper (95th) percentile of simulations shows a strong signal of increased water deficit by up to 30%, mostly in the current winegrowing regions. Intensified water deficit stress can represent a major threat for high-quality white wine production, as only mild water deficits are acceptable. Nevertheless, considerable variabilities of CWSI were discovered among RCMs, highlighting the importance of efforts towards reducing uncertainties in climate change impact assessment.

The invasive pest Drosophila suzukii is threatening berry production. It is mainly managed via chemical control, which is associated with consumer and environmental concerns. Here, we tested the efficacy of mineral dusts under field and laboratory conditions in 2019 and 2020. Furthermore, population dynamics were studied in a vineyard and its surroundings. The kaolin products Cutisan and Surround®, as well as the CaCO3 product Carboliq, had neither insecticidal nor repellent effects on Drosophila suzukii adults in laboratory choice tests with grapes at concentrations of up to 2% (w/v). Cutisan and Surround® significantly reduced the number of deposited eggs (−41.9% and −49.3% respectively) while Carboliq had no effect on the oviposition under laboratory conditions. The Surround® treatment significantly reduced the number of flies trapped on 09 September 2020 at a test vineyard. Depending on the assessment date and treatment, between 59% and 84% of the flies in the bait traps were females. The number of eggs found in fruit treated with Carboliq in the field was higher at each assessment date than in the control but this difference was not statistically significant. Fruit treated with Cutisan or Surround® in the field showed an equivalent or lower average number of eggs compared with the control, but this difference was only significant on 24 September 2020. Between May 2015 and October 2020, the highest number of D. suzukii adults was observed around September in the field and a decline of the population occurred in the winter months until July. In epidemic years, temperature – humidity – combinations prior to population peaks were quite stable with low humidity being associated with a high temperature and vice versa. In non‐epidemic years, humidity fluctuated more than in epidemic years and temperatures were lower before population peaks. The effect of global radiation on population maxima seemed to be minor.

Viticulture is exposed and vulnerable to extreme weather and climate change. In Europe, owing to the high socio-economic value of the winemaking sector, the development of adaptation strategies to mitigate climate change impacts will be of foremost relevance for its future sustainability and competitiveness. Some guidelines on feasible short-term adaptation strategies are provided here (Figure 1), collected by the Clim4Vitis action (https://clim4vitis.eu/). Long-term adapation startegies are described in an accompanying technical review.

In Europe, most of vineyards are managed under rainfed conditions, where water deficit has become increasingly an issue. The flowering-veraison phenophase represents an important period for vine response to water stress, which is known to depend on variety characteristics, soil and climate conditions. In this paper, we have carried out a retrospective analysis for important European wine regions over 1986–2015, with objectives to assess the mean Crop Water Stress Indicator (CWSI) during flowering-veraison phase, and potential Yield Lose Rate (YLR) due to seasonal cumulative water stress. Moreover, we also investigate if advanced flowering-veraison phase can lead to alleviated CWSI under recent-past conditions, thus contributing to reduced YLR. A process-based grapevine model is employed, which has been extensively calibrated for simulating both flowering and veraison stages using location-specific observations representing 10 different varieties. Subsequently, grid-based modelling is implemented with gridded climate and soil datasets and calibrated phenology parameters. The findings suggest wine regions with higher mean CWSI of flowering-veraison phase tend to have higher potential YLR. However, contrasting patterns are found between wine regions in France-Germany-Luxembourg and Italy-Portugal-Spain. The former tends to have slight-to-moderate drought conditions (CWSI<0.5) along with a negligible-to-moderate YLR (<30%), whereas the latter is found to have severe-to-extreme drought (CWSI>0.5) and substantial YLR (>40%). Wine regions prone to a high drought risk (CWSI>0.75) are also identified, which are concentrated in southern Mediterranean Europe. Advanced flowering-veraison phase over 1986–2015, could have benefited from more spring precipitation and cooler temperatures for wine regions of Italy-Portugal-Spain, leading to reduced mean CWSI and YLR. For those of France-Germany-Luxembourg, this can have reduced flowering-veraison precipitation, but prevalent reductions of YLR are also found, possibly due to shifted phase towards a cooler growing-season with reduced evaporative demands. Our study demonstrates flowering-verasion water deficit is critical for potential yield, which can have different impacts between Central and Southern European wine regions. This phase can be advanced under a warmer climate, thus having important implications for European rainfed vineyards. The overall outcome may provide new insights for appropriate viticultural management of seasonal water deficits under climate change.

Climate change is a major challenge to viticulture worldwide. The adaptation potential of the different strategies to cope with climate change still embraces many uncertainties (e.g., unpredictable social-economic developments and land-use changes), particularly in the long-term. However, adaptation strategies adjusted to local terroirs and regional climate change projections will contribute to the sustainable development of the winemaking sector. The Clim4Vitis action (https://clim4vitis.eu/) recommends some guidelines for long-term adaptation (Figure 1).

The training system Semi-Minimal-Pruned Hedge (SMPH) blends features of traditional Vertical Shoot Positioning-type (VSP) trellising systems with the concept of minimal pruning. While saving labor, this training system results in relatively high crop load and a poor leaf area to fruit weight-ratio (LFR), and thus, needs to be able to ripen grapes in a cool to moderate climate. For these reasons the impact of yield regulation strategies, including (i) shoot thinning (Darwin-Rotor), (ii) biotechnological thinning (Gibberellic acid), and (iii) bunch thinning (harvest machine) were trialed in a three year study at Geisenheim, Germany between 2017 and 2019 using Riesling (Vitis vinifera L.). The average yield per vine in SMPH (5.34 ± 1.10 kg) was 61.1% higher with a narrower LFR (14.01 cm2 g−1), compared with VSP (3.32 ± 1.02 kg, LFR: 16.99 cm2 g−1). The yield was successfully reduced and LFR simultaneously increased with shoot thinning (−33.1%, LFR: 19.04 cm2 g−1), biotechnological thinning (−18.3%, LFR: 16.69 cm2 g−1) and bunch thinning (−37.3%, LFR: 21.49 cm2 g−1). Ripening was delayed in SMPH. On average, two maturity thresholds (14.1 °Brix and 18.2 °Brix) were achieved 129 GDD (seven days according to the recorded daily mean temperatures, respectively) and 269 GDD (16 days) later in non-thinned SMPH, compared to VSP. All thinning treatments accelerated maturity progress ranging from 27 GDD (two days) to 58 GDD (three days) for 14.1 °Brix and 59 GDD (three days) to 105 GDD (six days) for 18.2 °Brix. Apart from immediate benefits on the economic efficiency, the adaption of the leaf area to fruit weight ratio using SMPH holds high potential to, (i) produce grapes targeting specific wine profiles and/or (ii) reducing the velocity of ripening under conditions of climatic change.

Increasing temperatures due to climate change are leading to advances in grapevine phenology and sugar accumulation in grape berries. This study aims to (i) determine if a temperature-based model can predict the time to target sugar concentrations from 170 to 220 g/L for Vitis vinifera L., (ii) use the best model to characterise the time to the specified target sugar concentrations for a wide range of cultivars with statistical evaluation of each cultivar's parameterisation, and (iii) establish cultivar classifications based on these thermal times to the specified target sugar concentrations. The Day of the Year (DOY) to reach the specified target sugar concentrations (170, 180, 190, 200, 210 and 220 g/L) was determined from time series of sugar concentrations collected from research institutes, extension services and private companies. Models were fitted for the species Vitis vinifera L. The two best-fit models for the DOY to reach the target sugar concentrations were selected using the Akaike Criterion (AIC) (evaluates model complexity and goodness of fit within one criterion) and assessed for model efficiency (EF) and error of prediction (RMSE, root means squared error) followed by a sensitivity analysis and model validation. The models were then parameterised for individual cultivars. The best model across all target sugar concentrations was the non-linear best Sigmoid model "best SIG"' model (parameters: start date (t(0)) = 86, d = -0.1294, e = 14.87). The best linear (Growing Degree Days) model was also selected which represents the model that required the least parameters and therefore the simplest in application for winegrowers. This model was termed the "Grapevine Sugar Ripeness" model (GSR) (parameters: base temperature (Tb) = 0 degrees C, start date (t(0)) = 91 or 1 April, Northern Hemisphere). Both models performed better than the Winkler and Huglin growing degree day models. Sixty-five cultivars were classified for the thermal time to one or more of the six sugar targets using these two models. Fifty percent of all combinations of cultivar and time to target sugar concentrations had EF values greater than 0.5 and RMSE values less than seven days. Confidence intervals were calculated for cultivars where there was sufficient data for the thermal time to target sugar concentrations. The classifications generated from both models provides the opportunity to implement either model to support cultivar choice in response to concerns of climate change and may provide cultivar solutions to issues of harvesting grapes at high sugar concentrations with resultant higher alcohol wines.

Budbreak date in grapevine is strictly dependent on temperature, and the correct simulation of its occurrence is of great interest since it may have major consequences on the final yield and quality. In this study, we evaluated the reliability for budbreak simulation of two modeling approaches, the chilling-forcing (CF), which describes the entire dormancy period (endo- and eco-dormancy) and the forcing approach (F), which only describes the eco-dormancy. For this, we selected six phenological models that apply CF and F in different ways, which were tested on budbreak simulation of eight grapevine varieties cultivated at different latitudes in Europe. Although none of the compared models showed a clear supremacy over the others, models based on CF showed a generally higher estimation accuracy than F where fixed starting dates were adopted. In the latter models, the accurate simulation of budbreak was dependent on the selection of the starting date for forcing accumulation that changes according to the latitude, whereas CF models were independent. Indeed, distinct thermal requirements were found for the grapevine varieties cultivated in Northern and Southern Europe. This implies the need to improve modeling of the dormancy period to avoid under- or over-estimations of budbreak date under different environmental conditions.

Present investigations aimed at developing a unified cumulative degree day based model approach allowing for (i) a precise simulation of grapevine phenological development of a broad range of cultivars and (ii) a classification of the cultivar specific relative precocity of different cultivars at different stages of grape development. Based on a long-term (7-year) data set of high-resolution phenological observations for 11 cool climate cultivars originating from Remich/Luxembourg, the unified phenological model (UniPhen) was developed using a cumulative degree day approach with three temperature thresholds (lower threshold: 10 degrees C; upper threshold: 20 degrees C; heat threshold: 30 degrees C). The average normalized standard deviation of UniPhen over all stages and cultivars was 5.26 corresponding to 5.26 days at 15 degrees C. In the cross-validated model, on average 53% of the observations were located in a range of +/- 3 days and 82% in a range of +/- 7 days (assuming daily mean temperatures of 15 degrees C) around the predicted date. The sequence of the cultivar-specific relative precocity was not stable over the different stages of phenological development. The model approach (i) enables a precise simulation of all 31 BBCH stages between beginning of the bud swell (01) and berries being ripe for harvest (89) for 11 cultivars grown in the climatic conditions of the Luxembourgish grapegrowing region and (ii) is open to being extended to other grape cultivars and re-calibrated under deviant climatic conditions. Due to their instability, a classification of the cultivars' relative precocity is only reasonable if it relates to a specific phenological stage. UniPhen represents a precise high-resolution phenological model approach and might be applied as a bioclimatic indicator describing the suitability of a location/region for the cultivation of specific cultivars.

The aim of the present investigations was to simulate the annual risk of bunch rot (Botrytis cinerea) on Vitis vinifera L. cv. Riesling grapes based on three long-term (n = 3 × 7 = 21 cases) assessment data sets originating from three Central European grape-growing regions. Periods when meteorological parameters were significantly (p < 0.01) correlated with the cumulative degree day (CDD7;18;24) reaching 5% disease severity were determined by Window Pane analysis. Analyses revealed five critical weather constellations ("events") influencing annual epidemics: relatively low temperatures after bud break, dry conditions during flowering, high temperatures after flowering, and low temperatures and high precipitation sums during/after veraison were all associated with thermal-temporal early epidemics. Meteorological data in each of the five events served as input for the bunch rot risk model "BotRisk." The multiple linear regression model resulted in an adjusted coefficient of determination (R2adj.) of 0.63. BotRisk enables (i) the simulation of the thermal-temporal position of the annual epidemic and, based on this, (ii) the classification of the annual bunch rot risk into three classes: low, medium, or high risk. According to leave-one-out cross-validation, 11 of 21 case studies were correctly classified. No systematic bias caused by location was observed, indicating that the transfer of the model into other locations with comparable climatic conditions could be possible. BotRisk (i) represents a novel viticultural decision support tool for crop cultural and chemical measures against bunch rot and (ii) enables an estimation of the bunch rot risk under changing environmental conditions.

Extreme heat events or heatwaves can be particularly harmful to grapevines, posing a major challenge to winegrowers in Europe. The present study is focused on the application of the crop model STICS to assess the potential impacts of heatwaves over some of the most renowned winemaking regions in Europe. For this purpose, STICS was applied to grapevines, using high-resolution weather, soil and terrain datasets from 1986 to 2015. To assess the impact of heatwaves, the weather dataset was artificially modified, generating periods with anomalously high temperatures (+5 °C), at specific onset dates and with specific episode durations (from five to nine days). The model was then run with this modified weather dataset, and the results were compared to the original unmodified runs. The results show that heatwaves can have a very strong impact on grapevine yields. However, these impacts strongly depend on the onset dates and duration of the heatwaves. The highest negative impacts may result in a decrease in the yield by up to −35% in some regions. The results show that regions with a peak vulnerability on 1 August will be more negatively impacted than other regions. Furthermore, the geographical representation of yield reduction hints at a latitudinal gradient in the heatwave impact, indicating stronger reductions in the cooler regions of Central Europe than in the warmer regions of Southern Europe. Despite some uncertainties inherent to the current modelling assessment, the present study highlights the negative impacts of heatwaves on viticultural yields in Europe, which is critical information for stakeholders within the winemaking sector for planning suitable adaptation measures.