Vineyard Floor Management and Cluster Thinning Inconsistently Affect ‘Pinot noir’ Crop Load, Berry Composition, and Wine Quality

Abstract

<jats:p>Growers of high-end ‘Pinot noir’ wine grapes (<jats:italic>Vitis vinifera</jats:italic> L.) commonly reduce yield by cluster thinning with the goal of increasing fruit quality; however, there are no objectively defined yield targets to achieve optimum fruit composition. Canopy leaf area relative to fruit yield can affect total soluble solids (TSS), and recommendations have been established for warm wine grape production regions. However, the relationship between leaf area and photoassimilation differs among climates and training systems. Leaf area to yield (LA:Y) ratios developed in warm, arid regions may not be suitable for cool, wet regions such as western Oregon. A 3-year field study was conducted to elucidate relationships between canopy to yield ratios and berry composition for ‘Pinot noir’. Vegetative growth and fruit yield were manipulated through competitive cover cropping and cluster thinning. Growth was manipulated in three ways: perennial red fescue (<jats:italic>Festuca rubra</jats:italic> L.) was grown in 1) both (Grass), 2) one (Alternate), or 3) neither (Tilled) of the alleyways flanking the vine row. Within each vineyard floor treatment, fruit clusters were thinned to one per shoot (Half Crop) or vines were left unthinned (Full Crop). Floor management influenced both canopy size and yield because of altered vine nitrogen (N) status. Effects of crop load on berry components were not always consistent between the crop load metrics used [yield to pruning weight (Y:PW) ratio or LA:Y]. In 2 years, TSS reached a maximum at similar LA:Y; however, this did not necessarily produce optimum TSS. Yield had the greatest influence on pH and total anthocyanins (ACY) in the highest yielding, coolest year. Crop load metrics were not reliable predictors of TSS because of the dominant effect of seasonal variation. Relationships between canopy to yield metrics and other berry components were partially explained by tissue N, photosynthetic photon flux (<jats:italic>PPF</jats:italic>) through the cluster zone, and/or yield. Cluster thinning to adjust yields may not alter source to sink relationships or canopy to yield ratios enough to overcome ripening limitations in cool climates. Only one wine vintage had sensory differences with Alternate-Half Crop and Alternate-Full Crop wines ranked high quality and Tilled-Half Crop and Tilled-Full Crop wines ranked low quality by both consumer and winemaker panels. Therefore, cluster thinning may have limited impact on wine sensory properties.</jats:p>

Evaluation of the Concord Crop Load Response for Current Commercial Production in New York

“…Crop loads below 7.2 did not result in an increase in juice soluble solids but did continue to increase vine size. This is consistent with other fruit thinning studies that showed little response of fruit maturation to crop load at Y:PW values below 10 and attribute fruit quality differences in this range to regional climatic conditions or seasonal variation (Keller M et al 2005, Preszler et al 2013, Reeve et al 2018). The crop load -Brix inflection point of 7.2 in this cool-climate study was slightly lower than the 10-12 reported in warmer climate studies (Kliewer and Dokoozlian 2005), supporting the theory that cool-climate grapevines need relatively more leaf area per unit fruit to reach maximum maturity.…”

“…Several cool-climate crop load studies have questioned the appropriateness of these crop load indicators in regions where more leaf area per unit fruit may be needed to achieve optimum fruit maturity and vegetative growth (Howell 2001); however, these studies have provided little evidence to deviate from the general crop load response. Fruit thinning studies with Pinot noir in Oregon and Merlot in Hawkes Bay, New Zealand (Y:PW ranges 0.5 to 3.7 and 3.4 to 9.0, respectively) indicated excessive vegetative growth and canopy density in the fruiting zone as having a larger impact on fruit composition than crop load and questioned the need for fruit thinning at these values (King et al 2015, Reeve et al 2018. Riesling crop load studies in NY and WA (Y:PW ranges 2.9 to 9.9 and 8.2 to 11.4, respectively) both showed slight delays in fruit ripeness at the highest crop load levels but questioned if the minor improvement in fruit quality from fruit thinning justified the economic cost in labor and crop loss (Keller et al 2005, Preszler et al 2013.…”

Agronomical and Chemical Effects of the Timing of Cluster Thinning on Pinot Noir (Clone 115) Grapes and Wines

“…Previous studies conducted on cluster thinning practices have applied variable yield reduction rates depending on cultivar. However, most research in Pinot noir has applied "half crop" treatments such as the one performed in the current study, removing all but the basal cluster on each fruiting shoot [34] or reducing cluster number by 50% [19].…”

“…Factors such as climatic variation in growing season [21] and viticultural practices such as floor management [34], deficit irrigation [21,22], and leaf thinning [74,75] have all been found to have a greater effect on fruit composition than cluster thinning. Indeed, in the present study, no consistent effect of cluster thinning or cluster thinning timing was observed across two growing seasons, a cooler growing season and a warmer growing season.…”

“…Despite the economic importance of Pinot noir on the central coast of California, no research has been undertaken to understand the relationship between Pinot noir crop load and fruit quality in the cool climate of San Luis Obispo county of the central coast. While research in cooler areas such as Oregon's Willamette Valley (USA) have indicated that grape ripeness increased in a curvilinear fashion with increasing LA/Y ratios up to 1.25-1.75 m 2 /kg [34], which is higher than the LA/Y ratios observed in warm climates [30], these source/sink ratios are intrinsically tied to the seasonal limitations of the region that result in inconsistent ripening and may not be translatable to more moderate cool climates such as California's central coast.…”