2017 ASHS Annual Conference

The incidence of solar radiation on red grapes can promote the synthesis of phenolic compounds desirable in wine production. However, an excess of solar radiation may induce oxidative damage and increase berry temperature. In such conditions, metabolites such as organic acids, flavonols, proanthocyanidins and anthocyanins may break down, leading to worsened quality. We performed a shade cloth trial aiming to evaluate if these can mitigate the deleterious effect of overexposure to solar radiation. The experiment was conducted in Oakville, CA on 'Cabernet Sauvignon' with a relaxed VSP in rows oriented NW to SE, covering the fruit zone with four polyethylene 1-meter curtains (20% shade Pearl, 40% shade Blue, 40% shade Red, 40% shade Black and 40% shade Aluminet) with different optical properties placed at the fruit zone and a control with no cover. Grape berries were sampled at six stages of development to determine berry mass, total soluble solids (TSS), pH, total acidity (TA), total flavonols, anthocyanins and proanthocyanidins. Berry temperature was 3.7°C higher on the west side of control compared to Black. Berry weight under the Aluminet was lower than the rest of the treatments. There was a non-significant trend in TSS where Pearl, Aluminet and control had higher values than Blue and Black. Berries under the cloths had often significantly lower pH and higher TA than control, but only Black shower significant effects at harvest. Berry anthocyanin content tended to be higher in under the nets, whereas flavonol content was significantly higher in Control. Proanthocyanidin content at harvest was higher in Black. Mean degree of polymerization (mDP) of proanthocyanidins was not affected by treatments. Our results provided evidence that shade cloths may mitigate temperature spikes while transmitting enough radiation into the fruit zone to achieve a better grape composition compared to uncovered grapes.