Anti-Hail Shading Net and Kaolin Application: Protecting Grape Production to Ensure Grape Quality in Mediterranean Vineyards

Abstract

Rising temperatures due to climate change pose a significant threat to viticulture, intensifying summer heat stress and accelerating berry ripening. Additionally, the increasing frequency of extreme weather events, such as hailstorms, further jeopardizes the sustainability of the viticultural sector. In recent years, mitigating these impacts has become crucial for grape production, particularly in Mediterranean regions. This study compares two mitigation strategies—using an anti-hail shading net (S) and kaolin spraying (K)—with untreated control vines (C) over three growing seasons. Vine physiology, berry ripening, grape production and pruning weight were evaluated. The S treatment significantly reduced light interception in the fruiting zone and, while limiting gas exchange, improved vine performance during extreme heat. The K treatment alleviated heat stress and enhanced the photosynthetic activity. Both S and K treatments improved grape quality by maintaining higher acidity levels and lower sugar concentrations and pH. Additionally, both treatments reduced the incidence of fungal diseases, with the net providing added protection against hailstorms. No significant changes in pruning weight were observed, and the treated vines showed a better balance between vegetative growth and production. In conclusion, both kaolin and shading nets are effective techniques for addressing the challenges of climate change, enhancing vine resilience and ensuring high-quality grape production.

1. Introduction

Climate change is unequivocally increasing air temperature, CO₂ atmospheric concentration and the frequency of extreme weather phenomena [1]. Worldwide, viticulture is highly endangered by these changes [2,3,4], particularly in warmer wine regions, like the Mediterranean, which are especially vulnerable [5].

One notable impact is the shortening of the growing season and the advancement of the phenological stages, with substantial effects on grape production [6]. Extreme temperatures during key growth phases can adversely affect the photosynthetic efficiency of leaves and disrupt berry metabolism [7]. Additionally, high temperatures negatively impact the grape quality, leading to unfavorable chemical compositions with increased sugar levels and reduced acidity [8,9]. Ultimately, this trend challenges winemaking as consumers tendentially prefer fresh and fruity wines with moderate alcohol content [10]. Furthermore, prolonged sunlight exposure can be detrimental for the grapes, affecting key quality compounds and leading to potential crop loss from sunburn [11,12]. This is particularly problematic for white grape varieties, which have a higher tendency of susceptibility to sunburns [13].

In this context, artificial shading has proven to be a valuable strategy for various fruit crops [14,15,16], and its effectiveness in grape production is well-documented [17]. Its primary effect is the reduction of irradiance on the canopy [18,19,20], which results in a reduction in the vine’s photosynthetic activity [12,21,22,23]. This reduction has positive effects on the vines’ water status, helping them to cope better with heat stress [24]. Consequently, shading can reduce berry dehydration [25,26], potentially resulting in increased yield at harvest [27]. However, some studies have reported a reduction in total yield for shaded vines [20,23,28], though it has been suggested that these variations could be attributed to a cultivar-specific response [29].

The reduction in photosynthetic activity due to shading results in lower sugar production. This is reflected in a delay in berry ripening, which leads to increased acidity at harvest [30,31], sometimes even associated with lower sugar concentrations [12,23,32,33,34,35]. Nevertheless, it is important to note that reduced sugar production can have negative implications for the vine’s accumulation of reserves and its growth in the following seasons [8,36]. Several studies reported limitations in carbohydrate allocation in the reserve organs due to reduced carbon assimilation in shaded vines [12,19,21,23,37]. In the long term, this might cause problems with spring growth and reduce the vine’s resistance to freezing temperatures [22].

Kaolin (Al₂Si₂O₅(OH)₄), originally developed for pest control in various tree and horticultural crops, is now widely used to mitigate abiotic stresses in viticulture as well [38]. It effectively minimizes summer heat stress [39], though its effectiveness is influenced by the grape cultivar [40]. Kaolin applications have been shown to reduce leaf and berry temperatures across various fruit crops [41,42,43,44], helping to maintain higher levels of net assimilation under heat stress [7,45,46,47,48,49]. Additionally, kaolin reduces water stress [45,47,48,50] by decreasing transpiration and preventing excessive water loss [41]. By reflecting light and reducing leaf temperature, kaolin lowers sugar concentration [7,40] and increases must acidity [47]. In warm climates, this overall better water status is reflected in higher berry weight [38,47,51], ultimately increasing the crop yield [52]. Moreover, as a pest control agent, kaolin has been shown to reduce the occurrence of downy mildew infections (Plasmopara viticola), both through direct inhibition and by activating the plant’s defense mechanisms [52,53], and the incidence of sour rot and gray mold (Botrytis cinerea) [54].

Considering the climatic peculiarities of Mediterranean environments and the challenges posed by climate change, it is crucial to provide farmers with effective tools to mitigate its effects and ensure sustainable production. For this reason, this study aims to investigate the effects of artificial shading and kaolin spraying on grapevine physiology and the subsequent impact on grape production over three consecutive years in the Mediterranean climate of central Italy.

2. Materials and Methods

2.1. Plant Material and Experimental Conditions

The trial was conducted over three consecutive years, from 2021 to 2023, in a four-year-old, rainfed, hillside (~20% slope) vineyard planted in 2017 and located in the Marche region, central Italy (elevation 190 m above sea level). Virus-free cuttings of Vitis vinifera L. cv Verdicchio (clone VLVR20) grafted onto 420A (Vitis berlandieri, Planch. × Vitis riparia Michx.) rootstock were used as sample vines. Plants were cane-pruned, vertically shoot positioned and trained in the unilateral Guyot training system, with N–NE to S–SE row orientation. The spacing was 3.0 m × 1.1 m, resulting in a density of 3030 vines/ha.

The vineyard was managed following the certified organic farming practices. Canopy management mainly consisted of a mechanical trimming of the shoots, performed around mid-June, when their length exceeded the top wires. No shoot thinning or bunch removal was performed.

The soil characteristics are summarized in

Table 1. Soil characteristics of the vineyard.

Parameter	Value
pH	8.1
Sand (g/kg)	303
Clay (g/kg)	339
Silt (g/kg)	358
Electrical conductivity (dS/m)	0.699
Organic carbon (g/kg)	7.4
Organic matter (g/kg)	12.8
Cation exchange capacity (Meq/100 g)	20.9

.

2.2. Experimental Design and Treatment Application

The trial was conducted using a randomized block design, with three treatments and three replicates of 8 vines (24 vines per treatment). Treatments consisted of (i) an untreated control (C), (ii) an anti-hail shading net application (S) and (iii) a kaolin spraying (K).

An anti-hail black net (Valente Srl, Padova, Italy), made of high-density polyethylene (HDPE 100%), with a height of 100 cm, a monofilament texture and an unchangeable rectangular mesh size of 2.8 × 8 mm, was applied vertically on both sides of a row with the aim of protecting the vines from meteorological events and reducing the incident solar radiation on the canopy of the plants. The dimensions of the net do not change when subjected to hail loads. The black net has a high mechanical resistance, a long lifespan (guaranteed for 10 years) and a shading capacity of 15%. The net was placed manually every year after fruit set (namely 17 June 2021, 7 June 2022 and 6 June 2023).

Kaolin was applied for two out of three years of the study, beginning in 2022 in anticipation of heatwaves, using Kaolin Surround WP (produced by Tessenderlo Kerley Inc., Phoenix, AZ, USA) with a kaolin content of 95%. In 2022, kaolin was sprayed twice during the season, as the first application did not fully cover the vines’ canopy, and it was washed out by a rainfall shortly after. The first treatment was applied at the beginning of July at a dosage of 8 kg/ha, while the second was applied at the beginning of August at a dosage of 25 kg/ha. In 2023, kaolin was applied once at a dosage of 25 kg/ha at the beginning of July. The treatment covered the entire canopy, and it was applied using a low-volume sprayer attached to a tractor.

2.3. Gas Exchange and Light Interception

During the trial, the photosynthetically active radiation (PAR) inside the canopy of both C and S vines was measured. The measures were taken at full canopy development and under saturating light [photosynthetically active radiation (PAR) > 1200 μmol photons m⁻² s⁻¹] with an AccuPAR PAR/LAI Ceptometer Model LP-80 (Decagon Devices, Inc., Pullman, WA, USA). Measures were taken at noon on 29 July 2021 and 25 August 2022 by placing the ceptometer inside the canopy at the cane level and parallel to it.

Leaf gas exchange was measured in the morning, between 9:00 and 12:00 solar time. Measures were taken on mature leaves inserted in the middle portion of the main shoot, well-exposed to light, and under saturating light conditions (PAR > 1200 μmol photons m⁻² s⁻¹) using an Open-Path Infrared Gas Analyzer LCA3 (ADC BioScientific, Hoddesdon, England). Carbon assimilation rate (A_N), stomatal conductance (g_s) and transpiration (E) were recorded upon reaching the stabilization of the CO₂ differential. Intrinsic water use efficiency (WUEi) was derived by ratioing net assimilation (A_N) and stomatal conductance (g_s).

2.4. Berry Ripening, Grape Composition and Vine Yield

Berry ripening was monitored from the end of veraison (indicatively at the end of July) until harvest. Total soluble solids [TSS (°Brix)], pH, titratable acidity [TA (g/L)] and malic acid concentration [MA (g/L)] were analyzed weekly. Samples of 100 berries per replicate were collected and transported to the laboratory. Berries were weighed and crushed, and the juice was used for the following analyses. TSS was determined using a temperature-compensating Maselli LR-01 digital refractometer (Maselli Misure, Parma, Italy). Must pH was analyzed with a Crison two-decimal pH meter (Crison Instruments, Barcelona, Spain) by means of a glass electrode; TA with a Crison Titrator (Crison Instruments) using 0.25 N NaOH (Carlo Erba Reagents Srl, Cornaredo, Italy) to a pH 7.00 endpoint, expressed as g/L of tartaric acid equivalent. The malic acid concentration was analyzed through an enzymatic kit (Enzyplus-Raisio, Raisio, Finland).

Harvest took place on 8 September 2021 [Day of the year (DOY) 251], 29 August 2022 [DOY 241] and 27 September 2023 [DOY 270]. Grapes were manually picked, and the total number of bunches per vine was counted and weighed. Average cluster weight was calculated as the ratio between total yield per vine and the total number of bunches per vine. Samples of 100 berries per vine were collected and weighed to determine the average berry weight. The berries were then taken in the laboratory and crushed, and the juice was analyzed as previously described.

Since the meteorological trend of 2023 promoted the development of bunch diseases (i.e., Botrytis cinerea and Plasmopara viticola), the incidence of fungal diseases was assessed. A total of 24 clusters per treatment (1 cluster per sample vine) were used, and the level of infection was visually determined and expressed as a percentual ratio.

Annual vine growth was further assessed during winter pruning. Surveys were conducted on the same sample vines previously harvested. Two shoots were selected to be left as fruiting canes for the next year, and the rest were removed, counted, and weighed. The number of buds left in each fruiting cane was counted and used to determine bud fertility by calculating the ratio between the number of buds left and the number of shoots counted in the following year. The average weight of the shoots was obtained by dividing the total weight by their number on each plant. The Ravaz index [55], commonly used to evaluate the balance between vine growth and yield, was finally calculated as the ratio between the weight of the harvested grapes and the weight of the pruned shoots for each sample plant.

2.5. Hail Damage and Pruning Weight

On 8 August 2023, the vineyard was severely damaged by a hailstorm, and the extent of the damage was determined. The evaluation was made by considering 8 shoots on 8 different vines for both control (C) and netted (S) vines. Each shoot was divided into four different portions: from the base to the fourth node (I), from the fifth to the eighth node (II), from the ninth to the twelfth node (III) and above the thirteenth node (IV). In each section, the presence of damage on the vine’s organs was assessed.

Annual vine growth was evaluated during winter pruning. Surveys were carried out on the same sample vines that were previously harvested. Shoots not kept as fruiting canes for the following year were removed, counted, and weighed. The number of buds left in each fruiting cane was counted and used to determine bud fertility by calculating the ratio between the number of buds left and the number of shoots counted in the following year. The average weight of the shoots was calculated by dividing the total weight by their number on each plant. Finally, the Ravaz index [55] was calculated to assess the balance between vine growth and yield and was derived by the ratio between the weight of harvested grapes and the weight of the pruned shoots for each sample plant.

2.6. Meteorological Data

Meteorological data were obtained from the Regional Meteorological-Hydro-Pluviometric Information System (SIRMIP) provided by the Civil Protection Service of the Marche Region. The selected meteorological station was Moie (Station Code 506; 43°29′ N, 13°7′ E; elevation 104 m a.s.l.), from which daily minimum, average, and maximum temperatures were recorded (Sensor Code 3021). Rainfall data were sourced from the meteorological station of Cupramontana (Station Code 118, 43°26′ N, 13°6′ E; elevation 510 m a.s.l.; Sensor Code 1263) as cumulative daily precipitation values. These data were processed to calculate, for each month, the number of days when the maximum temperature exceeded critical thresholds of 30 °C and 35 °C, as well as the monthly average values of minimum, average and maximum temperatures and the growing degree days (GDD).

2.7. Statistical Analysis

Statistical analysis was performed using R version 4.3.1—package “agricolae” [56]. For each year, data were subjected to one-way analysis of variance (ANOVA). When the results of ANOVA were significant at p ≤ 0.05, data were subjected to Tukey’s HSD test. Graphical representations were obtained using Sigma Plot version 10 (SPSS, Chicago, IL, USA).

In the figures, trends for gas exchange, berry mass, TSS, must pH, TA, and MA are shown as mean values.

3. Results

3.1. Meteorological Trend

The meteorological data are summarized in

Table 2. Meteorological conditions for the three years of study.

	2021	2022	2023
Rain (mm/year)	754	702	908
Rain from budbreak to harvest (mm)	94	154	596
Rainy days from budbreak to harvest (n°)	22	22	51
Average summer a temperature (°C)	25	25	24
Days with max. temperature > 30 °C (n°)	65	85	69
Days with max. temperature > 35 °C (n°)	23	16	20
GDD b April–October	2121	2287	1661

^a summer was defined as the period from 1 June to 31 August for each year of the study; ^b GDD—Growing degree days (average daily temperature base 10 °C).

. Over the three years of the trial, average summer temperatures were comparable. However, 2022 stood out as the hottest year, characterized by the highest frequency of heatwaves. On the other hand, 2023 had a milder climate, as reflected by the total growing degree days (GDD).

The most notable variability among seasons was observed in rainfall patterns. Although the annual precipitation in 2021 and 2022 was nearly identical, the rainfall during the critical period from budbreak to harvest was notably scarcer in 2021. In contrast, 2023 exhibited a markedly different trend, with significantly higher rainfall and humidity. During the growing season alone, precipitation reached 596 mm. Additionally, on 8 August 2023, a severe hailstorm caused extensive vineyard damage, significantly impacting the vintage. This event contributed to the proliferation of fungal pathogens, which had considerable repercussions on grape production for that year, as will be discussed later. Figure 1 provides a clearer illustration of the varying precipitation trends over the three years for the period spanning from June to the end of September.

3.2. Canopy Light Interception

Light interception was notably influenced by the application of the net (Figure 2). In both years, photosynthetic active radiation (PAR) was reduced both at the outer canopy layers and in the fruiting zone when compared to fully exposed vines.

Specifically, PAR at the canopy sides was reduced by 129 μmol photons m⁻² s⁻¹ (approximately 21%) in 2021 and by 130 μmol photons m⁻² s⁻¹ (around 17%) in 2022, slightly exceeding the net’s 15% shading capacity as initially reported. Interestingly, due to the combined shading effect of the net and the canopy’s leaf layers, light interception in the fruiting zone saw a more pronounced reduction. In 2021, PAR measured 508 μmol photons m⁻² s⁻¹ for C and 114 μmol photons m⁻² s⁻¹ for S, marking a reduction of almost 78%. In 2022, the light intensity in the fruiting zone was 465 μmol photons m⁻² s⁻¹ in C and 31 μmol photons m⁻² s⁻¹ in S, indicating a reduction of nearly 93%.

3.3. Leaf Gas Exchange

The trends for stomatal conductance and net assimilation in different treatments are depicted in Figure 3. In 2021, no difference between the treatments was observed, with only a slight reduction observed in S during the central part of the summer. The treatment’s effect became more pronounced starting from the second year. On the initial measurement date, stomatal conductance (g_s) remained unchanged between C and K, both recording values of 0.03 mol H₂O m⁻² s⁻¹, while S showed a significant reduction to 0.02 mol H₂O m⁻² s⁻¹. As the season advanced, C experienced a marked decline in stomatal conductance, dropping to 0.02 mol H₂O m⁻² s⁻¹. In contrast, g_s for K and S remained relatively stable, measuring approximately 0.03 mol H₂O m⁻² s⁻¹ and 0.04 mol H₂O m⁻² s⁻¹, respectively. By the end of the season, g_s in K and S declined while C exhibited a recovery, ultimately surpassing the other treatments by 0.02 mol H₂O m⁻² s⁻¹.

In 2023, the stomatal conductance values were generally higher compared to previous years. At the start of the season, control vines exhibited the lowest g_s, measuring 0.090 mol H₂O m⁻² s⁻¹, while both kaolin-sprayed and shaded vines showed significantly higher values of 0.120 and 0.134 mol H₂O m⁻² s⁻¹, respectively. Similarly, at the end of the season, C recorded the year’s lowest g_s value, whereas both K and S maintained significantly higher stomatal conductance. Throughout the rest of the season, no significant differences in g_s were observed among the treatments.

In 2021, the use of the net significantly reduced net assimilation (A_N) on all measurement dates, except for the final one, where values for both treatments were nearly identical (Figure 3). This reduction in A_N is consistent with the decreased irradiance reaching the canopy due to the shading net. At the beginning of 2022, K exhibited the highest A_N, with 11.31 μmol CO₂ m⁻² s⁻¹, while we noted a significant decrease in S, which only reached 7.08 μmol CO₂ m⁻² s⁻¹. Afterwards, during the central part of summer, A_N dropped in all treatments, though the reduction was more contained in K and S. At the end of the season, the net assimilation for C was the highest, while both K and S exhibited lower values, indicating a recovery of photosynthetic functionality in control vines with temperature decrease.

In 2023, the variability between treatments was less pronounced, with values generally ranging between 7 and 12 μmol CO₂ m⁻² s⁻¹. Generally, both K and S reduced the vine’s photosynthetic activity, as A_N values were lower for most of the season.

The trends for intrinsic water use efficiency (WUEi) and transpiration (E) in different treatments are depicted in Figure 4. In 2021, WUEi did not differ between control vines (C) and shaded vines (S), with C showing only marginally higher values for most of the season. Similarly, in the subsequent two years, no significant differences were detected between the two treatments, although shading resulted in slightly higher WUEi during the drier season of 2022. Although significant differences with the control were observed only once, the effect of kaolin was slightly more pronounced than that of shading nets (S) in improving the WUEi. In 2023, the effects of kaolin on WUEi were less pronounced, likely due to the more humid conditions that characterized the season. Under these conditions, control vines experienced reduced water stress, minimizing the relative benefits of kaolin application.

The transpiration trends (E) mirrored those observed for stomatal conductance. The highest E values were recorded in 2023, whereas 2022 saw the most significant reduction in vine transpiration. Throughout 2021, the transpiration rates for C and S vines were nearly identical, fluctuating between 1 and 2 mmol H₂O m⁻² s⁻¹. Similarly, in 2022, no significant differences in transpiration were observed between treatments for most of the season. However, consistent with the stomatal conductance trends, C exhibited a marked decrease in E during the middle of summer, while K and S maintained slightly higher values. The only significant difference occurred on the final date, where C recorded the highest transpiration rate (1.17 mmol H₂O m⁻² s⁻¹), while both K and S showed reduced transpiration on treated vines, resulting in values of 0.67 and 0.70 mmol H₂O m⁻² s⁻¹, respectively.

3.4. Berry Ripening

In 2021, berry weight was slightly lower in S compared to C, though the difference was not significant for most of the season (Figure 5). By harvest, the differences diminished, and no significant variations were observed, although S berries remained the lightest. The pattern in 2022 differed notably from the previous year. Early in the season, the berry weights were nearly identical across all treatments. However, in the latter half of the season, the growth in berry weight slowed for C, whereas both K and S maintained a steady increase. Post-harvest observations revealed a distinct trend: C and K vines experienced berry dehydration, marking losses of 0.10 g and 0.21 g, respectively, compared to their harvest weight. On the other hand, S exhibited no post-harvest dehydration, maintaining a constant berry weight. In 2023, no significant difference between treatments was observed except for the harvest date, when S exhibited the highest berry weight.

The total soluble solids (TSS) evolution is shown in Figure 5. In 2023, ripening was slower than in the previous two years due to the specific climatic conditions of that season. In 2021, TSS accumulation was rapid in control vines, while shading significantly reduced TSS for most of the season, with the largest reduction of 4.07 °Brix on day 232 of the year. By the end of the season, the TSS levels between treatments converged, resulting in identical values at harvest. In 2022, the treatment effects were more pronounced, with significant differences persisting throughout the entire season. Control vines consistently exhibited the highest TSS, while both K and S significantly reduced sugar accumulation. These differences became more pronounced as the season progressed and until the harvest. Even two weeks after harvest, treated vines maintained significantly lower TSS compared to the control, with 2.9 °Brix less for K and 3.8 °Brix less for S. The same trend was observed in 2023 as well. Early in the season, treated vines showed significantly lower TSS than controls, with shading having a slightly greater effect than kaolin. This pattern persisted until harvest, with kaolin and shading lowering the TSS by 0.6 °Brix and 1.2 °Brix, respectively.

The evolution of the acidic components throughout the study is illustrated in Figure 6. Although initially titratable acidity (TA) values were similar between treatments, shading significantly slowed the reduction of organic acids, resulting in consistently higher TA levels. As the season advanced, the differences between treatments became less pronounced, though at harvest, differences between treatments were still significant. In 2022, at the start of the season, both S and K had slightly higher TA compared to C, though these differences were not statistically significant. From the second sampling date (02/08), the differences became significant, with shaded vines exhibiting the highest TA at 19.8 g/L, followed by kaolin-treated vines at 16.6 g/L, and control vines showing the lowest TA values. This trend persisted throughout the season until harvest. Even after the harvest, the highest TA was observed in K (6.6 g/L), followed by S (6.2 g/L) and C (6.1 g/L). Similarly, in 2023, significant differences in TA were recorded from the beginning of the season. Shaded vines had the highest initial TA (+4.7 g/L compared to C), followed by kaolin-treated vines (+3.4 g/L compared to C). Although all treatments experienced a decrease in TA as the season progressed, both K and S consistently maintained significantly higher values throughout the rest of the season.

The treatments also affected malic acid (MA) concentration. S significantly slowed down the degradation of malic acid, leading to higher levels across all seasons. In 2021, the impact of shading was most evident during mid-ripening, while in 2022, significant effects persisted close to harvest. Notably, post-harvest measurements showed that shaded vines had 0.49 g/L of malic acid, while control and kaolin-treated vines had 0.22 and 0.23 g/L, respectively. Although kaolin’s effect on malic acid was less pronounced than shading, it still increased the malic acid concentration, especially during the first half of the season. Significant differences between K and C persisted up to harvest. In 2023, both S and K consistently resulted in higher MA compared to C throughout the entire season, with shading generally showing the highest values.

The evolution of must pH is depicted in Figure 7. Mirroring the trend observed for the acidic components, control vines, which consistently had the lowest acidities, generally exhibited the highest pH values throughout the years. In 2021, S resulted in lower pH values on every date except the first one. Consistent with the results obtained in the previous year, in 2022, S significantly reduced the must pH. Even two weeks after harvest, the shaded vines maintained the lowest pH at 3.08, while the control vines exhibited a higher pH of 3.18. On the other hand, kaolin did not significantly affect the must pH on any of the sampling dates. In 2023, both K and S began to significantly influence the must pH from the second half of the season onward. This resulted in treated vines displaying consistently lower pH values compared to C by the end of the season.

3.5. Vegetative Growth and Hail Damage

Table 3. Vine vegetative parameters in control (C), kaolin (K) and shading (S) treatments during the survey (2021–2023).

Treatment	Buds/vine (no.) a
	2021	2022	2023
C	nd *	12 a	11 a
K	nd	12 a	11 a
S	nd	12 a	11 a
Treatment	Shoots/vine (no.) a
	2021	2022	2023
C	13 b	11 b	13 a
K	nd	13 a	15 a
S	15 a	14 a	14 a
Treatment	Bud fertility a
	2021	2022	2023
C	nd	0.90 b	1.20 b
K	nd	1.07 ab	1.35 a
S	nd	1.15 a	1.31 ab

^a Values between rows followed by different letters are significantly different (p < 0.05) according to Tukey’s test. * nd = not determined.

summarizes the vegetative parameters recorded throughout the trial period. In 2021, S had a higher number of shoots per vine compared to C. However, since data on the number of buds per vine and bud fertility for that year are not available, it is unlikely that this difference was due to the shading treatment, as the net was only applied at the end of fruit set—after the number of shoots per vine had already been established. To ensure consistency during the subsequent years, the pruning was adjusted to leave the same number of buds for each treatment—12 buds per vine in 2022 and 11 in 2023. Despite this standardization, in 2022, the control vines exhibited a significantly lower number of shoots per vine compared to treated vines, resulting in a higher bud fertility for treated vines. In 2023, bud fertility remained positively influenced by the treatments. Both K and S increased the bud fertility compared to the control. As a consequence, although the differences in the number of shoots per vine were not statistically significant that year, both S and K still resulted in a slightly higher number of shoots per vine compared to the control.

As mentioned before, on 8 August 2023, the vineyard was struck by a hailstorm. To assess the effectiveness of the anti-hail shading net, the extent of the damage was measured and is reported in

Table 4. Incidence of hail damage in 2023 on four sections of the canopy: I (from the first to the fifth node), II (from the fifth to the eighth node), III (from the ninth to the eleventh node) and IV (above the twelfth node). C indicates the untreated control; S indicates anti-hail shading treatment.

Section	Treatment	Damage (%) a
I	C	79 a
	S	0 b
II	C	75 a
	S	13 b
III	C	75 a
	S	50 b
IV	C	88 a
	S	94 a
TOTAL	C	77 a
	S	40 b
I–III	C	77 a
	S	28 b

^a Values between rows followed by different letters are significantly different (p < 0.05) according to Tukey’s test.

. Generally, a clear pattern of increased damage from the base to the top of the shoots was observed, with the upper sections suffering more than the lower ones. In Section I, S completely prevented the damage, while control vines experienced a substantial 79% damage. In Sections II and III, the net provided significant protection, with damage limited to 13% and 50%, respectively, compared to 75% in C for both sections. However, both C and S were heavily impacted in Section IV, with damage rates of 88% for the control and 94% for the shaded vines. This section was only partially protected as the net, measuring 100 cm in height, did not provide full coverage for the entire canopy. When focusing on the first three sections (I–III), which were fully covered by the net, the effectiveness was evident: exposed vines suffered nearly 80% damage, while the anti-hail net reduced the damage to about one-third in shaded areas. This reduction had a positive impact on grape quality by minimizing crop loss and limiting pest development on damaged berries, as will be discussed later.

3.6. Yield Components and Grape Composition at Harvest

The grape yield parameters are shown in

Table 5. Vine yield components and fungal disease development in control (C), kaolin (K) and shading (S) treatments during the survey (2021–2023).

Treatment	Clusters/vine (no.) a
	2021	2022	2023
C	13 b	14 b	15 a
K	nd *	19 a	19 a
S	17 a	20 a	15 a
Treatment	Yield/vine (kg) a
	2021	2022	2023
C	3.9 a	3.3 b	2.8 b
K	nd	4.6 a	4.3 a
S	4.0 a	5.1 a	4.0 a
Treatment	Cluster weight (g) a
	2021	2022	2023
C	305 a	234 a	182 b
K	nd	245 a	238 a
S	234 b	249 a	257 a
Treatment	Berry weight (g) a
	2021	2022	2023
C	1.65 a	1.61 b	1.97 ab
K	nd	1.73 a	1.89 b
S	1.47 a	1.68 ab	2.01 a
Treatment	Berries/cluster (no.) a
	2021	2022	2023
C	184 a	148 a	93 b
K	nd	144 a	130 a
S	160 a	148 a	126 a
Treatment	Plasmopara viticola incidence (%) a
	2021	2022	2023
C	nd	nd	4 a
K	nd	nd	1 b
S	nd	nd	1 b
Treatment	Botrytis cinerea incidence (%) a
	2021	2022	2023
C	nd	nd	4 a
K	nd	nd	2 b
S	nd	nd	1 b

^a Values between rows followed by different letters are significantly different (p < 0.05) according to Tukey’s test. * nd = not determined.

. In 2021, berry weight at harvest was slightly lower in S compared to C, although the difference was not statistically significant. However, combined with the fewer berries per cluster, this contributed to a significantly lower cluster weight in shaded vines. Despite these differences, the overall grape yield per vine was comparable, with S at 4.0 kg per vine and C at 3.9 kg per vine. This parity was likely due to the higher number of clusters per vine in S, driven by the increased number of shoots per vine in that year (Table 3), which offset the reductions in cluster and berry weight. In 2022, the differences in cluster count persisted, with both K and S producing more clusters per vine than C. Even though pruning was standardized across treatments, the lower bud fertility observed in C led to a reduced number of shoots per vine (Table 3), resulting in fewer clusters. Furthermore, berry weight was significantly higher in both S and K compared to C. With the number of berries per cluster consistent across treatments, the increased berry weight in treated vines directly enhanced the cluster weights. These factors, combined with the greater cluster counts, significantly boosted yields in treated vines. The kaolin-treated vines achieved a yield increase of approximately 39%, while shading resulted in a 55% increase compared to the control. In 2023, S had a pronounced effect, significantly increasing the berry weight at harvest and the cluster weight. On the other hand, K slightly reduced the berry weight compared to C but still led to higher cluster weights due to an increased number of berries per cluster. Consequently, both treatments achieved significant yield improvements, with increases of 43% for S and 54% for K compared to the control. The meteorological conditions for 2023, characterized by high humidity and frequent rainfall, heavily influenced grape production. These conditions, coupled with the hailstorm on 8 August, created an environment favorable to fungal diseases. Despite this, clear differences between treatments were observed in the incidence of diseases on the harvested grapes. Control vines, despite having fewer berries per cluster—which might have reduced the bunch compactness and improved the microclimate within clusters—suffered with the highest number of damaged clusters due to severe infections by downy mildew (Plasmopara viticola) and gray mold (Botrytis cinerea). In contrast, both S and K significantly mitigated disease incidence, highlighting their protective effects under adverse conditions.

Grape composition at harvest is depicted in

Table 6. Grape composition in control (C), kaolin (K) and shading (S) treatments during the survey (2021–2023).

Treatment	Total soluble solids (°Brix) a
	2021	2022	2023
C	20.7 a	22.0 a	25.1 a
K	nd *	19.8 b	23.9 b
S	20.7 a	17.9 c	24.5 ab
Treatment	pH a
	2021	2022	2023
C	3.23 a	3.09 a	3.39 a
K	nd	3.13 a	3.31 b
S	3.02 b	2.99 b	3.32 b
Treatment	Titratable acidity (g/L) a
	2021	2022	2023
C	6.80 b	6.01 b	6.28 b
K	nd	6.18 b	6.85 a
S	7.73 a	6.90 a	6.76 a
Treatment	Malic acid (g/L) a
	2021	2022	2023
C	0.35 a	0.25 c	1.42 a
K	nd	0.45 b	1.59 a
S	0.38 a	0.60 a	1.54 a

^a Values between rows followed by different letters are significantly different (p < 0.05) according to Tukey’s test. * nd = not determined.

. Shading effectively delayed ripening across all years, resulting in overall underripe grapes at harvest. Although sugar concentration was the same between S and C in 2021, shaded vines exhibited significantly higher titratable acidity (TA), representing a nearly 14% increase, and a lower must pH. In 2022, shading further delayed ripening, reducing the sugar concentration by 4.1 °Brix. Additionally, shading increased the TA and malic acid (MA) concentrations, with respective increases of 0.89 g/L and 0.35 g/L. The must pH was also lower in shaded vines (2.99) compared to the control (3.09). In 2023, although the difference in sugar concentration between treatments was less pronounced than in the previous year, shading still resulted in lower sugar levels compared to the control. TA remained higher in S, while pH was lower. Across all treatments, the malic acid concentrations in 2023 were higher than in previous years due to the cooler and wetter conditions of the season, which limited its degradation. This explains why no differences in malic acid concentration were observed between S and C, as the humid, mild weather reduced malic acid depletion in control vines.

For kaolin, in its first application year (2022), sugar concentrations were reduced by 2.2 °Brix (approximately 10% less than the control). However, unlike shading, kaolin did not significantly affect TA or must pH, which were similar to the control. Nevertheless, kaolin reduced malic acid depletion, resulting in higher concentrations compared to C (0.20 g/L more). In 2023, K again reduced the total soluble solids content. Unlike in 2022, it positively influenced both TA and pH, creating significant differences compared to C. Similar to shading, no difference in malic acid concentration was observed in 2023 due to the climatic conditions of that season.

3.7. Pruning Weight

Vine reserve accumulation was assessed through winter pruning (

Table 7. Vine pruning parameters in control (C), kaolin (K) and shading (S) treatments during the survey (2021–2023).

Treatment	Pruning weight/vine (kg) a
	2021	2022	2023
C	1.1 a	0.9 a	1.4 a
K	nd *	1.1 a	1.4 a
S	0.9 a	1.0 a	1.7 a
Treatment	Cane weight (g) a
	2021	2022	2023
C	85 a	84 a	104 ab
K	nd	85 a	95 b
S	61 b	73 a	122 a
Treatment	Ravaz index a
	2021	2022	2023
C	3.7 a	3.9 b	2.1 b
K	nd	4.3 ab	3.2 a
S	4.9 a	5.2 a	2.6 ab

^a Values between rows followed by different letters are significantly different (p < 0.05) according to Tukey’s test. * nd = not determined.

). In 2021, shading resulted in a lower average cane weight compared to the control, primarily due to the higher number of canes per vine. However, the total pruning weight was comparable between treatments. In 2022, individual cane weight was similar across treatments, as well as pruning weight per vine. Despite the uniform pruning weights, the Ravaz index for the control remained significantly lower at 3.9, indicating reduced productivity, as reported in Table 5. In 2023, although pruning weight was similar, the cane weight varied across treatments. The Ravaz indices in 2023 were the lowest in the entire trial period, likely due to the reduced crop levels caused by the adverse climatic conditions discussed earlier. The control vines had the lowest Ravaz index at 2.1, while the kaolin-treated and shaded vines maintained higher indices of 3.2 and 2.6, respectively.

4. Discussion

The primary effect of using shading nets is the reduction of light irradiance within the canopy and fruiting zone [17,18,20]. The results of this trial are consistent with these findings. However, it is important to emphasize that even moderate shading levels, as applied in this study, can significantly alter the fruiting zone’s microclimate. This occurs because light is obstructed not only by the shading net but also by the leaves. As a result, grapes can be effectively protected from excessive radiation without experiencing the negative effects associated with high levels of light exclusion, which have been reported by some researchers [18,22]. By lowering the light irradiance, shading also limits gas exchange [12,21,22,23]. Similarly, with the use of the anti-hail shading net (S), stomatal opening was restricted, reducing gas exchange in treated vines, particularly net assimilation. Interestingly, an inversion of this trend occurred during the central part of summer 2022, where shading led to higher values of both stomatal conductance and net assimilation. As previously noted, 2022 was particularly dry compared to the other seasons. Our hypothesis is that shading enhanced vines’ resistance to heat stress, while untreated vines experienced more stress, as observed by other authors [24]. In these conditions, control vines were forced to close their stomata to minimize water loss, thereby limiting their ability to carry out photosynthesis efficiently.

Shading also had an impact on the vegetative growth of the vines. While differences observed in 2021 cannot be attributed to the shading treatment, as it was applied after fruit set—well after shoot formation and development—shading resulted in higher bud fertility in 2022 and 2023. It has been noted that under reduced light conditions, vines often stimulate shoot vigor to compensate for decreased photosynthetic activity, which can come at the expense of bud development for the following year [21,57]. However, evidence suggests that in hot environments, shading can improve the vine’s microclimate, alleviating heat stress and promoting better bud fertility [58,59]. These studies support the findings of this trial, as bud fertility was enhanced in shaded vines. Additionally, it is important to emphasize that we applied a relatively low level of shading (15%). This may also help explain why, in our case, bud fertility was not negatively affected as in the aforementioned studies, where greater shading intensities were used.

The capacity of shading to delay berry ripening has been extensively documented, leading to lower sugar concentrations, higher acidities and lower pH levels [12,23,30,31,32,33,34,35,60]. The results of this study align with these findings. Even with a low level of shading, berry ripening was significantly delayed across all three years of the trial. This resulted in underripe grapes at harvest, characterized by lower total soluble solids content and higher acidities.

Shading also significantly increased the berry weight, particularly in the drier season of 2022, when it also prevented berry dehydration at the end of the vintage after harvest. This aligns with findings from other studies [25,26,27], suggesting that in hotter and drier seasons, shading may enhance the berry water content and, ultimately, the vine yield. Additionally, in 2023, the anti-hail shading net provided effective protection against hail damage, resulting in higher grape production compared to the control. This treatment also contributed to a lower incidence of fungal diseases, highlighting its multifaceted benefits in potentially ensuring stable production during challenging vintages.

As documented by other authors, the primary downside of shading is that by reducing the sugar production, it can negatively impact reserve accumulation and allocation, potentially causing critical issues for the subsequent growing seasons [18,21,22,23,37,61]. Contrary to these findings, we did not observe reductions in pruning weight for shaded vines during the survey. We hypothesize that this differing response can be attributed to the low level of shading applied in our study. This moderate shading likely reduced the sugar production to a level that did not adversely affect reserve accumulation. This hypothesis is further supported by the Ravaz index values, which, apart from 2023—when results were influenced by unique meteorological conditions—indicate well-balanced vines overall.

The kaolin-treated vines demonstrated improved gas exchange and water use efficiency, particularly during heatwaves like the one experienced in 2022, due to the protective effects of the particle film. These findings align with previous studies [7,38,45,46,47]. However, it has been noted that this beneficial effect tends to diminish under less stressful conditions [46,62]. Similarly, in our trial, as temperatures declined and stress conditions subsided, no significant improvements were observed in kaolin-treated vines compared to the control. This was particularly evident in 2023, a year characterized by higher water availability due to frequent rainfall, which mitigated heat stress compared to the previous year.

By reducing water stress, kaolin resulted in higher berry weight and yield in 2022, consistent with findings from other studies [38,47,51,52]. However, in 2023, berry weight from the kaolin-sprayed vines was the lowest among all treatments. It has been reported that in humid climates, kaolin can negatively affect berry weight [53]. This suggests that seasonal meteorological variability influences kaolin’s effectiveness in enhancing berry weight, with its benefits being diminished during particularly humid seasons, such as in 2023. Nevertheless, in such vintages, kaolin still proves beneficial as it effectively reduced fungal infections due to its pest-control capacity [52,53,54], ultimately resulting in an increased crop load. Although its effect was less pronounced than shading, kaolin slowed down berry ripening, resulting in grapes with higher acidities and lower sugar concentrations. This outcome aligns with findings from other studies [40,45,47], further supporting kaolin’s role in moderating the ripening process under specific conditions. Nevertheless, carbon allocation was not impeded, as kaolin-treated vines exhibited pruning weights similar to the controls. Additionally, the Ravaz index values for kaolin-treated vines were closer to the optimum than those of the control, indicating an overall better balance in treated vines.

5. Conclusions

The results of this trial highlight that both shading nets and kaolin applications are valuable tools for mitigating summer stress and preserving grape production and quality.

Kaolin efficacy seems strongly dependent on environmental conditions. During heatwaves, it enhances vine resilience by reducing stress symptoms and improving photosynthetic activity and water use efficiency, thus reducing berry dehydration and increasing yield. On the other hand, in more humid and rainy seasons its efficacy is diminished, though it still proves useful in controlling pest development. It effectively delays berry ripening, resulting in grapes with higher acidities and lower sugar concentrations at harvest.

Shading, by lowering irradiance, limits gas exchange, further reducing photosynthetic activity and sugar production. However, under extreme heat, shaded vines can maintain improved photosynthetic performance, showing their utility in mitigating excessive temperatures. Moreover, the positive effects on the microclimate also showed benefits for vegetative growth, thus increasing bud fertility.

Shading significantly delayed berry ripening, resulting in lower total soluble solids content and higher acidity with lower pH at harvest. When combined with anti-hail functionality, shading nets provide additional benefits by reducing hail damage, promoting grape health, and limiting disease incidence.

Contrary to findings from other studies, shaded vines in this trial showed no negative impact on reserve accumulation, likely due to the low-intensity shading used. This level of shading appears to strike a balance, delaying berry ripening without compromising the vine’s carbohydrate reserves.

In conclusion, although the implications of their use on red grape varieties require further consideration, particularly regarding the effects on anthocyanin and polyphenol concentrations, both kaolin and shading prove to be valuable techniques to address the effects of climate change in white grape production, particularly in regions like Central Italy with a Mediterranean climate. Each method offers distinct advantages, and their use can be tailored to specific climatic and economic conditions, ultimately benefiting grape quality and production.