Spring frost is a perennial and widespread problem across many cool climatic and high-elevation winegrowing regions of the world. Vitis vinifera L. cv. Pinot noir is an early budding cultivar; thus, it is particularly susceptible to late-spring frost damage. In late April 2022, an advective frost event occurred throughout Western Oregon winegrowing regions and subsequently damaged a substantial number of commercial vineyards. Growers often are unsure of how to manage grapevines after a frost event. Limited research has shown little-to-no effect of pruning vs. non-pruning strategies on vine yield and productivity. In addition, pruning a frost-affected vineyard incurs additional labor costs that may offset the cost–benefit balance for the grower. Therefore, in this experiment, the effect of two different post-frost pruning treatments (cane pruning and spur pruning) on vine yield, berry composition, and vine vegetative growth were tested. No effect of post-frost pruning treatments on vine yield, berry composition, and vine vegetative characteristics was observed. Cluster numbers, cluster weights, and berries per cluster only differed between cane- vs. spur-pruned vines. Therefore, leaving frost-affected vines alone and a scaled-back vineyard management practice could be practical for economic reasons.

Background and goals Grapevine red blotch virus (GRBV) is a major pathogen of Vitis vinifera L. that causes the eponymous grapevine red blotch disease (GRBD). This disease is characterized by reduced leaf carbon assimilation and delayed berry ripening, resulting in diminished fruit quality. Recent work suggests that the virus alters leaf carbon metabolism prior to emergence of visible symptoms. However, the physiological manifestation of this altered metabolism is currently unknown. Therefore, an experiment was conducted to unravel the progression of GRBD symptoms in field-grown Pinot noir grapevines. Methods and key findings Diurnal and seasonal measurements were conducted to quantify changes in leaf carbon balance and chronologize symptom progression in leaves and fruit. Leaf-level physiology was measured as a function of water relations, photosynthesis, and nonstructural carbohydrates in a commercial vineyard containing both healthy and infected vines. Additionally, fruit sugar and anthocyanin accumulation were monitored during ripening. Virus infection reduced carbon assimilation pre- and postveraison, but the effect was more pronounced postveraison and during the afternoon. Similarly, virus infection significantly increased leaf starch concentration pre- and postveraison. Starch granules accumulated in the chloroplasts and caused apparent damage to their structural and functional integrity. The virus had no sustained impact on chlorophyll fluorescence, suggesting that changes in fluorescence were a transient response to reduced carbon assimilation and export. Conclusions and significance This study provides evidence that GRBV infection causes starch accumulation in infected leaves, which may have downstream effects on leaf carbon metabolism and ripening prior to the appearance of visible symptoms.

Background and goals Pinot noir is one of the most popular winegrape varieties worldwide, but because of its origins in more cool-climate wine production regions, there is little information regarding its responses to regulated deficit irrigation practices in warm and semiarid climates. Thus, the objective of this study was to observe the responses of Pinot noir production and fruit quality characteristics to preveraison (anthesis to veraison) and postveraison (veraison to harvest) deficit irrigation over two growing seasons. Methods and key findings Treatments consisted of pre- and postveraison irrigation levels at fractions (25, 50, 75, and 100%) of estimated crop evapotranspiration (ET_c). Vine water status (stem water potential [Ψ_stem]) was strongly correlated with applied irrigation during both periods, but particularly during preveraison. Accordingly, berry weight was significantly and linearly reduced with preveraison deficit irrigation, but there was no significant berry weight response to postveraison deficit irrigation. All skin phenolic compound classes—anthocyanins, tannins, and iron-reactive phenolics—showed an inverse linear relationship with preveraison deficit irrigation rate, while these responses to postveraison deficit irrigation were quadratic, both on a concentration and a content basis. With preveraison deficit irrigation, a negative linear relationship was observed between berry phenolics such that the greatest preveraison deficit had the highest total phenolics. In contrast, berry phenolic composition improved with moderate postveraison deficit irrigation and no negative yield effects were observed. The preveraison irrigation rate of 25% of ET_c and postveraison rates between 50 to 75% ET_c maximized berry phenolics without a significant reduction in vine yield. Conclusions and significance In summary, the results indicate that severe deficit irrigation preveraison, and mild to moderate deficit irrigation postveraison, improve berry phenolics in warm-climate Pinot noir.