Kiley Osterman and Patricia Skinkis*
*Oregon State University, 2750 SW Campus Way, Corvallis, OR, 97331 
(patricia.skinkis@oregonstate.edu)

Cluster thinning is common in winegrape production and was conducted historically in Oregon Pinot noir to hasten ripening and ensure quality. Industry standard yield targets in the early 2010’s were 4.5 to 6.2 t/ha, and growers questioned those thresholds. To systematically evaluate the effect of cluster thinning on fruit composition and wine sensory perception, a research project was conducted by Oregon State University and >20 vineyard and winery companies from 2012 to 2021. The impact of this research was quantified using a series of surveys, interviews, and focus group meetings to gather information about individual, company, and industry-wide changes to yield management practices. Project collaborators increased yield targets, as there were no consistent differences in berry ripeness at harvest and a lack of differences in wine quality between crop thinning treatments. There were no vine health consequences of maintaining higher yields (dormant pruning weight or vine nutrient status). By the mid-point of the study, the industry began adjusting yield targets based on season variability, rather than a constant tonnage/ha. This was due to the observation that wine quality was more influenced by vintage variation and winemaker than by vineyard crop thinning practices. Most collaborators reported little-to-no difference in wine sensory perception between crop thinning levels. Although most project collaborators felt comfortable increasing yields by 1.24 to 7.71 t/ha without compromising quality, obstacles such as winery capacity and sales limited further adoption for some. Often, target yields were set to fit winery and sales capacity, leading to target yields that did not reflect vineyard yield-quality potential. Project collaborators improved management and vineyard knowledge and expressed a desire to share findings. The project had industry-wide impact with greater yields reported at the state level and greater tolerance of increasing yield targets by growers and winemakers alike.

Funding Support: Northwest Center for Small Fruits Research