UC Davis

This study was conducted to evaluate the efficacy of using photoselective shade films as a climate change impact mitigation practice in microirrigated vineyard systems in 2020 and 2021. Four photoselective shade films with varying transmission spectra (D1, D3, D4, D5) were compared to a control treatment (C0) consisting of uncovered grapevines. Net carbon assimilation and stomatal conductance were unaffected by shade films despite the photosynthetically active radiation (PAR) being reduced approximately by 20%. Additionally, fruit yield, total soluble solids, pH and titratable acidity were unaffected by shade films in either experimental year. Ultimately, shade films which reduced near infrared radiation increased anthocyanin concentration by 27% in 2020, the hotter of the two experimental years due to cluster temperature reduction of 9oC. Improved flavonoid profiles observed in grapes at harvest was directly transmitted to resultant wines. Additionally, wines obtained from the D4 treatment exhibited a more fruity and pleasant aroma profile than wines from the C0 treatment. To segue from artificial shading vineyard interventions to utilizing the vine’s natural shading capacity via canopy architecture, the water footprint of six trellis systems under three irrigation amounts was evaluated from 2020 to 2022, as there is a lack of information surrounding vine water requirements for various trellis systems commonly used in hot wine grape production regions. Vine water use efficiency was improved with reductions in applied water amounts. Additionally, single high wire (SH) trellis systems had the highest crop water use efficiency in all experimental years due to increased yield. Applied water amounts and trellis systems effected total water footprint and its components. The 25% ETc treatment had lower blue water footprint in all three years but greater WFgrey and WFtotal compared to 50% and 100% ETc treatments. In 2020, SH trellis systems had the lowest WFblue. In 2021, WFtotal and its components were reduced in single high wire and high quadrilateral (HQ) trellis systems. Ultimately, there was no significant effect of trellis on WFtotal and its components in 2022. Under severe drought conditions, vines grown with single high wire trellis systems under irrigation regimes corresponding to replacement of 50-100% ETc were able to sustain yields and carbohydrate allocation. In light of a climate that is increasingly variable and the reduction of an available and trainable labor force, SH irrigated to 50-100% of ETc provided adequate fruit yield as well as a reduction of WFtotal and amelioration of WUEc. Overall, this study provided information to support the need for heat mitigation strategies under future climate change conditions in hot viticulture regions. Shade films proved to be viable option for premium grape and wine producers to maintain and improve fruit and wine quality against increasing frequency and severity of heat wave events. Subsequently, reduced water availability, either by drought or increasingly stringent environmental regulations, will require adaptation measures to restore vineyard water balance. Our study provided information supporting the application of deficit irrigation strategies and trellis systems to improve vineyard water use efficiency. In conclusion, single high wire trellis systems irrigated with a water amount corresponding to at least 50% ETc replacement can reduce the total water footprint of the vineyard system without compromising profitable fruit yield and composition, thus providing a viable solution to mitigate the effects of both increasing air temperatures and reduced water supply that result from an increasingly variable and changing climate.