There are myriad environmental and physiological factors that may impact yield in a given season. Growers in Oregon’s cool climate are often concerned about how the weather at bloom may affect yield; however, vine nutrient status or overall vine health may be having a greater impact on fruit set and fruitfulness (number of clusters per shoot), both of which can influence yield. In her Oregon Wine Board funded research project entitled “Impact of vine vigor, nitrogen and carbohydrate status on the fruitfulness of Pinot noir,” Dr. Patty Skinkis and her co-investigators examined how these factors may be influencing bud fruitfulness, specifically the number and size of floral initials established within the bud.
This research arose from findings within a vineyard floor management study that had been conducted in a commercial vineyard in the Willamette Valley from 2007-2014. After observing changes in cluster size and relative fruitfulness between the different experimental treatments, Dr. Skinkis began investigating how vine vigor, as a result of the vineyard floor management, impacted bud fruitfulness. They also included experiments to understand the impacts of lateral shoot removal and cluster zone leaf removal on bud fruitfulness, as both practices may alter vine carbohydrate accumulation.
The research involved collecting dormant canes and examining them for the number and size of inflorescences per bud. Following bud-break, vines were monitored to determine actual fruitfulness per shoot. Finally, vines were monitored for growth and nutrition, and trunks and roots sampled for nitrogen and carbohydrates throughout the season.
The researchers determined that vines grown with grass cover crop in every row for a long-term had lower nitrogen status, smaller canopies, more light infiltration, and slightly smaller inflorescences within the bud compared to the higher vigor vines that were grown with tilled soil, which led to lower yields. Dr. Skinkis is continuing these studies to understand the physiology at play between seasonal vine nitrogen and carbohydrate status and floral development within Pinot noir buds.
Understanding how cultural factors impact bud fruitfulness has important practical implications for wine grape growers. What happens one season can have an important impact on the next season’s crop level, particularly when floral development begins more than a year before fruit is harvested!