This year, Cornell University and the New York State Agricultural Experiment Station celebrate 100 years of cool-climate viticulture research in the Lake Erie production region of western New York. For a large portion of those years, the focus has been on vine size management as a way of improving vine productivity, juice quality and grower profitability. Nelson Shaulis established long ago in Concord vineyards that vine size is the key to success, but little research has been done in New York on how to reach the ideal vine size in the more expensive winegrape varieties. Below we'll present new results from trials with Riesling, Traminette, Cabernet Sauvignon and Noiret.

Shaulis on pruning weight

Early research on nutrient and pest management improved overall vine health and productivity; however, it was not until the 1950s that Shaulis researched and promoted the use of vine pruning weight as a management tool in New York's Concord vineyards.

Vine size is measured as the weight of dormant cane prunings on a per-vine, per-row unit, or a per-canopy unit basis. For example, in the New York Concord industry, it is common to hear growers talk about 2-pound, 3-pound or 4-pound vines to characterize vine growth. The concept is that vine-pruning weight is a measurement of vine vegetative growth and an indicator of potential leaf area production and canopy fill. A 3-pound vine, for example, will produce more leaf area, intercept more sunlight and have higher yield because of greater bud fruitfulness than a 1-pound vine, holding all other factors constant. However, "all other factors" in vineyards (such as spacing, soil, variety, rootstock, etc.) are rarely constant.

Shaulis ran a series of pruning, spacing and rootstock trials to find the optimum pruning weight for Concord grapevines, which turned out to be 0.35 pounds of dormant cane prunings per foot of row (or 0.52 kg/m). Vines with fewer prunings did not sufficiently fill the allotted trellis space for optimum production, and vines with significantly more prunings produced excessive leaf area for the allotted trellis space, leading to internal canopy shading, decreased bud fruitfulness and lowered fruit quality.

Shaulis divided excessively large vines through Geneva Double Curtain training to take advantage of the excess leaf area production and intercept more sunlight per unit land area. Kliewer and Dokoozlian, in their review of grapevine crop load and fruit quality in the American Journal of Enology and Viticulture, also reported optimum vine size at 0.5-1.0 kg/m.

Shaulis gave us a robust target for desired vine growth. On the one hand, defining the target is an achievement; but hitting the target, and doing it consistently, is a greater challenge. Vine size is directly influenced by the supply and uptake of water and mineral nutrients. Water and nutrient availability is a function of the physical, chemical and biological characteristics of the soil, while uptake is a function of root activity and genetics (i.e., rootstocks).

Vine size is indirectly influenced by crop load through the partitioning of assimilated carbon into either vine vegetative or reproductive organs. Furthermore, genetic differences in grape scion varieties have their own growth potential characteristics. With all the inter- and intra-variation in vineyard sites, soils, root pests, water and nutrient-management options, rootstock selections and varietal characteristics, it is no wonder that New York viticulturists after Shaulis have spent considerable effort researching how to hit the optimum vine size of 0.5 kg/canopy meter.

Winegrape trial began in 2003

While the majority of nutrition, water and rootstock research projects in New York have been conducted with Concord grapevines, one current experiment addresses the issue of vine size management on potential winegrape varieties for the region. The winegrape trial was planted in 2003 at the Cornell Vineyard Laboratory in Fredonia, N.Y., on a well-drained gravel-loam soil with 2% organic matter. It is a multi-factorial experiment with two soil pH levels (unlimed pH~5, and limed pH~6), four root systems (own-rooted, Riparia Gloire, Gravesac and 3309 Couderc), and four varieties (White Riesling, Traminette, Cabernet Sauvignon and Noiret).

The Lake Erie grape belt is characterized by a mixture of acidic gravel-loam and clay-loam soils (~4.5-5.5 soil pH). Recent research with Concord shows that low soil pH in these vineyards increases toxic aluminum and decreases beneficial potassium, magnesium, calcium and phosphorus availability, leading to decreases in vine size and productivity.

Amending the soil pH with limestone can greatly improve the availability of these essential mineral nutrients and increase vine size. Taking yet another cue from Concord research, rootstock trials show how own-rooted Concord can struggle to reach acceptable vine size without close attention to water and nutrient management, while Concord grafted to 3309C rootstock (a common rootstock choice in the Northeast) can grow excessively large, especially in wet seasons.

Therefore, in addition to own-rooted and 3309C in the current winegrape planting, Riparia Gloire was added as a devigorating stock for vine size control, and Gravesac was added for its potentially acid-tolerant characteristics. For scion variety selections, Traminette and Noiret are two inter-specific hybrid varieties from Bruce Reisch's grape-breeding program at Cornell University. Riesling was added because of its growing popularity as a signature variety for New York. Although most would argue the growing season in western New York is too short for Cabernet Sauvignon, the variety name recognition continues to drive its market value, and we wanted to document just how mature the fruit would get in the region under optimum vine size conditions.

During the course of three mature cropping seasons (2006-08), the various combinations of soil pH, rootstock selec tion and scion varieties have resulted in a wide range of vine sizes, with cane prunings from 0.0-1.7 kg/row meter (corresponding to canopy descriptors of "near dead" to "monster jungle," respectively). More quantitative methods of canopy assessment, such as point quadrant and image analysis, were used to measure the relationship between vine size and canopy characteristics. In 2008, a side-facing Normalized Difference Vegetation Index (NDVI) sensor also was used for this purpose. The relationship between vine size and NDVI indicates optimum canopy fill for all varieties around the optimum vine size number of 0.5 kg/m (or 0.35 pounds/foot).

Recommendations from trials

The million-dollar question for a vineyard manager in New York is: What combination of soil and root management will result in optimum vine performance? The answer: the combination that gives you 0.5-0.7 kg/m vine size, of course. Although the general relationships recorded in this study will most likely hold up across many vineyard sites in the Northeast (e.g., 3309C grafted vines will be larger than Riparia grafted vines when all else is held equal), the specific combination to grow optimum vine size will be highly site specific based on the water and nutrient availability of the site. Recommendations for sites similar to the Cornell Vineyard Lab along the Lake Erie gravel-loam bench would look like this:

 

A nutrient-deficient Riesling leaf (right) looks much different than a healthy sample.

RIESLING: Riesling vines in the experiment struggled to reach optimum vine size in most of the treatment combinations (See table above). Unlimed plots showed magnesium and phosphorus nutrient deficiencies, both visually (right) and in tissue samples. Only the more vigorous rootstocks (Gravesac and 3309C) with soil pH limed to ~6.0 reached an average vine size of 0.5 kg/m.

TRAMINETTE: Some commercial Traminette vineyards are being planted own-rooted, which may be acceptable if the site has high growth potential. In this trial, own-rooted Traminette vines were too small on average for optimum production. Otherwise, five of the remaining six treatment combinations gave acceptable pruning weight measurements. As a side note, this variety consistently had the lowest tissue magnesium levels compared to the other varieties. Increasing soil pH and Mg availability with limestone helped increase Mg tissue levels. Gravesac rootstock also increased tissue Mg and P more than the other rootstock selections, making it a potentially good match with Traminette.

CABERNET SAUVIGNON: This variety showed the most dramatic response to the treatment combinations compared to the other varieties. Own-rooted vines in unlimed blocks were either dead or close to it, while vines grafted to Gravesac or 3309C in limed blocks were excessively large. The devigorating character of Riparia Gloire rootstock hit the 0.5 kg/m sweet spot with Cabernet Sauvignon at this experiment site. The one caution I offer is to remember that Riparia Gloire is shallow and drought susceptible. I would only recommend using it if supplemental irrigation was also in the management plan. However, the combination of Riparia Gloire with irrigation potentially increases the level of vigor control for many New York vineyards that are currently dry farmed.

NOIRET: Noiret is a newly released variety, and we still have much to learn about optimizing its production. In general, average vine size was above 0.5 kg/m on all of the rootstock selections. Own-rooted Noiret was significantly smaller than the grafted vines, but could probably be improved with slightly more aggressive nutrient and water management.

In conclusion, Shaulis identified the optimum vine size needed for New York vineyards. Water, mineral nutrient and rootstock research, similar to the experiment described in this article, have developed the tools needed to manipulate the size of any individual vine. The future challenge in vineyard vine size management is to be able to identify and respond to spatial and temporal vine size variation in vineyards.


Dr. Terry Bates is a viticulture research associate with the Cornell University Department of Horticultural Sciences. Contact him at (716) 672-2175 or trb7@cornell.edu. To comment on this article, e-mail edit@winesandvines.com.