Grape yield regulation is a method used to improve grape quality parameters. Experiments were carried out in 2021 on the grapevine (Vitis vinifera L.) wine varieties 'Feteasca regala' and 'Sauvignon blanc', focusing on the effect of two different methods of grape yield regulation on its selected parameters and must sugar content. The first method used was cluster thinning, leaving one bunch on the shoot. The next method used was cluster tipping when we removed the terminal part of each bunch. Yield reduction was carried out in the period between pea-sized berry phenophase (BBCH 75) and bunch closure phenophase (BBCH 77). The operations were carried out manually. Cluster thinning did not lead to a statistically significant difference in bunch weight compared to the control in any of the studied varieties. We observed a statistically significant (p <0.05) decrease in the average bunch weight in the variant cluster tipping. The 'Feteasca regala' hectare yield was 32.25% lower in the cluster thinning than the control. The hectare yield in the cluster thinning variant was reduced by 46.61% compared with the control. Cluster thinning variant of the Sauvignon blanc variety had a 19.13% lower yield than the control variant. The cluster tipping variant had a 29.03% lower yield than the control variant. In the case of the cluster thinning method, we observed a greater decrease in grape yield compared to the cluster tipping method. The obtained results indicate that cluster tipping method is preferable to the cluster thinning in terms of the profitability of grape production. The must sugar content was statistically significantly (p <0.05) increased in all the yield reduction variants. The variety 'Feteasca regala' had the highest sugar content of the must in the cluster thinning method, 19.42 kg/hL. The highest sugar content of 'Sauvignon blanc' was 21.33 kg/hL in the variant with cluster tipping. This shows that regulating the grape yield can improve the quality parameters of the grapes. On the other hand, it may lead to a decrease in yield per hectare below the break-even point. The justness and intensity of the method used must be carefully considered.

Grapevine growth and physiological performance are strongly influenced by biotic and abiotic stresses occurring during the growing season. Plant stimulants are increasingly applied in viticulture as management tools aimed at supporting plant physiological processes and improving plant performance under variable environmental conditions; however, cultivar-specific responses to different application strategies remain insufficiently characterized. The aim of this study was to evaluate the effects of foliar plant stimulant application strategies differing in application frequency and phenological timing on selected physiological and canopy-related indicators in Slovak grapevine cultivars (Vitis vinifera L.) under field conditions. The assessed parameters included leaf chlorophyll a and b contents, chlorophyll a/b ratio, leaf area index (LAI), vegetation indices (NDVI and PRI), cluster weight, and basic must composition. Grapevines were subjected to three treatment variants: a control without plant stimulant application, a variant with two foliar applications, and a variant with three foliar applications of commercial biostimulants (Tecamin Max, Tecamin Flower, and Tecamin Brix) performed at key phenological stages during the growing season. Plant stimulant applications were associated with variations in leaf chlorophyll content and LAI values, particularly under repeated application strategies. NDVI and PRI complemented leaf-level measurements by capturing cultivar-dependent differences in canopy condition and photosynthetic regulation throughout the season. Responses of cluster weight and must composition to plant stimulant application were moderate and varied among cultivars, indicating cultivar-specific responses. Although no consistent increase in cluster yield was observed, treated variants showed higher sugar content and lower titratable acidity in several cultivars, indicating differences in grape composition and ripening-related traits. Overall, the results indicate that foliar plant stimulant application strategies can influence physiological and canopy-level grapevine traits in a cultivar-dependent manner. The combined use of leaf-level, canopy-level, and spectral indicators provides a practical framework for evaluating plant stimulant strategies under field conditions and supports their application in sustainable viticulture.

Grapevine trunk diseases represent a serious threat to viticulture, posing substantial challenges to the sustainability and productivity of vineyards. Fungal pathogens associated with the grapevine trunk diseases complex decompose the wood matter in grapevine trunks, leading to the disruption of vascular tissue integrity and the subsequent disruption of water and nutrient translocation within the plant. The aim of the work was to compare the yield and qualitative parameters of musts and wines from symptomatic and asymptomatic grapevines. The grape originated from the Nitra wine-growing district, from varieties Riesling Italico and Cabernet Sauvignon, aged 17 years, were used. Grapes from symptomatic and asymptomatic grapevines were processed into must and wines. The differences in yield quantity and physicochemical parameters of must and wine were analysed. Fourier transform infrared spectroscopy was used to analyse the physicochemical parameters. To test the statistical significance of the results, the Tukey’s test (p ≤ 0.05) was applied. Symptomatic grapevines of Cabernet Sauvignon exhibited significantly lower cluster weight and yield compared to asymptomatic grapevines, with a decrease of 504.71 g per bush. For Riesling Italico, no significant difference in yield was found. The must from symptomatic grapevines had significantly lower total sugar content, with Cabernet Sauvignon showing a decrease of 51.29 g/L and Riesling Italico a decrease of 23.72 g/L, along with higher acidity in Cabernet Sauvignon (+1.54 g/L). These findings confirm that grapevine trunk diseases exert a detrimental effect on both yield and must quality, with notable variability observed between grape varieties.