Wines & Vines

GRAPEGROWING This leads us to question whether Oregon's generally low fruitfulness and variable fruit set are related to the high vine vigor that is prevalent and not just poor weather during bud development or flowering. This question is being addressed in current and future vine balance studies. Management practices to reduce vigor through nitrogen-competition have been explored in Oregon. In a six-year trial using different vineyard floor management practices in Pinot Noir, a grass cover crop in tractor rows has helped reduce vine nitrogen-status compared to 100% tilled tractor rows, thereby influencing vegetative growth, fruitfulness and fruit set. Vines grown with perennial grass cover had reduced shoot growth rate, leaf area, pruning weight and tissue nitrogen. By year four of the study, clusters in vines grown with grassed tractor rows were smaller than other treatments by 6-12 grams per cluster, but these vines had a higher percentage of fruit set. The grass did not decrease fruitfulness and number of flowers per inflorescence until years five and six, when the vines were near-deficient in tissue nitrogen. This suggests that nitrogen has an important role in flower development, both in formation of floral primordia in the buds and flowers that develop in the following growing year post-bud break. While changes in development of primary fruit yield are interesting for long-term management of vineyards, Lateral crop is visible as it begins to ripen in the upper canopy above primary clusters in the fruit zone. 82 p racti c al w i ne ry & v i n e yard AU G U ST 20 13 the growth of fruit from lateral shoots (see photo) is nearly as important to consider on both physiological and management levels. Lateral crop Development of clusters on lateral shoots that arise from the main shoot — In many cases, growers view lateral crop as a nuisance to manage. It can hang into the fruit zone, where it can be mistakenly picked with the primary crop, and requires additional cluster-thinning TreatmentFruit (-) lateral crop (+) lateral crop (+) lateral crop primary clusters lateral clusters growth such as increased shoot length, lateral development or lateral crop, all of which can be influenced by increased auxin production. To understand true vine balance, both primary and lateral crop fruit was quantified in addition to vine size metrics (vine leaf area, pruning weight, cane weight and yield) within vine balance studies in Oregon. Both the 2010 and 2012 growing seasons resulted in lower than average fruit set across Oregon, and a greater quantity of lateral crop was observed Cluster Weight (g) % colorTSS (°Brix) pHTA (g/L) 92.2 100 22.7 3.31 8.6 98.2 100 23.0 3.36 8.2 13.7 52 11.3 2.69 30 Table 1. Cluster weights and maturity of primary clusters that had lateral crop removed at véraison, primary clusters that had lateral crop left on the vine, and the composition of lateral crop clusters at harvest, as measured Oct. 2, 2012. passes to remove it before harvest. This can pose problems for mechanical harvesting if the berries shake off and join the primary crop berries in the hopper. This fruit often lags in development and can dilute quality of the final harvest.2 From the physiological perspective, the vine's goal is to produce fruit to pass along its progeny. Vines are not concerned about quality or degree of ripeness. When the crop level is low, there is a shift toward increased production of lateral crop. This shift has been observed in vine balance research trials conducted with Oregon Pinot Noir. Where vine yield and vigor were manipulated by cluster thinning or vineyard floor management, there was a shift in lateral shoot growth and fruit development from laterals when the crop load was particularly low. While many research studies have been conducted regarding yield management, few studies have reported specific impacts related to vine size or crop level on lateral shoot growth or lateral crop development. Most work regarding lateral crop development has been related to cultural practices or exogenous hormone use to enhance flowering and fruit set.1,5,6 Work on auxin-enhanced transgenic vines shows that auxin has a role in increasing both fruitfulness and fruit set in cultivars that typically have low bud fruitfulness.3 However, this work did not report any increase of vine vegetative by growers and quantified in vine balance studies conducted in those years. The average fruit set in several research trials within the same vineyard was 45%-55% in 2010 and 43%-45% in 2012, compared to 65%-84% in 2011, a high fruit set and yield year. Cultural practices utilized in a vineyard floor management study had a large impact on lateral shoot growth and crop development. Vineyard floor management practices (perennial grass in tractor rows, alternate tilled and grass tractor rows, and tilled tractor rows) affected shoot growth, vine size and yield. In 2012, vines within 100% tilled treatments had increased primary shoot growth (length and rate of growth), more lateral shoot development and longer lateral shoot length. Some lateral shoots produced their own laterals! High vegetative vigor status of vines where the vineyard floor was tilled may be creating issues with flowering and fruit set, as they had a lower percentage of fruit set in primary clusters compared to other treatments in the study. However, cluster size did not vary greatly from other treatments at harvest. The consequence of this lower crop level relative to the large canopy size combined with high shoot vigor was an increase in canopy growth, and production of more clusters on lateral shoots. Vines grown with grassed tractor rows (moderate vigor) and vines in alternatetilled tractor rows (moderate-high vigor)

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