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Resistant Rootstocks for New York Vineyardspage 2Managing Vigor of Vinifera Vineyards |
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Vinifera as a class are more vigorous than the other varieties we grow in New York. They are lime tolerant, but do not tolerate acid soils well (for more on soil pH and vinifera growth). We have not identified acid tolerant rootstocks for vinifera scions, and suggest raising the pH of vinifera vineyard soils to at least pH 6.5.
Vinifera vine vigor in NY
Because our cool season climate sometimes can border on frigid, the primary goal for most of our growers is to ensure early maturity of both the fruit and the vine. Failure to do so will result in a loss of quality and increased winter cold damage. In addition, because New York is a region of summer rainfall, irrigation systems are rare and disease pressure is high. In our situation growers must strive to optimize all available management decisions so that the quality potential of the grapevine is expressed. Too often growers put excessive emphasis on the impact of a single practice on vine vigor. No matter how important or influential it is, no single tool can guarantee success. Success depends upon making appropriate decisions about a whole series of cultural practices which have interrelated influences on vine growth. One of these decisions is the choice of rootstock.
Vine size versus vine vigor
These two terms have had quite precise and distinct definitions which are detailed in A.J. Winkler's book, General Viticulture. In Winkler's usage, vine size refers to the weight of cane prunings produced by a vine during a growing season; it is a measure of the vine's overall growth capacity. Vine vigor refers to the rate of shoot growth. However, in recent years the distinction between the two terms has become blurred. I now tend to use both interchangeably to refer to the amount of vegetative growth a vine makes during a growing season.
Problems of the low vigor vineyard
Because there are many more vinifera vineyards with excessive vigor than with inadequate vigor, low vigor is often thought of as a goal rather than a problem. However, I have seen vinifera vineyards with inadequate vigor in every viticultural area I have visited in the world. Inadequate vigor is a serious problem and the cause(s) should be identified and corrected. Except when very close row spacing is used, vineyards with vines that have less than 0.2 lbs cane prunings/foot of canopy will produce low yields of inferior quality fruit. Their buds and trunks also have reduced cold hardiness.
Problems of the high vigor vineyard
The vines of an excessively vigorous vineyard have more than 0.6 lbs of cane prunings/foot of canopy. On such vines, shoot growth is prolonged, resulting in a dense canopy of leaves and the diversion of photosynthates from the developing fruit and vine carbohydrate reserves to investment in superfluous vegetative growth. Bud and cane maturation is delayed resulting in low cold hardiness and sometimes reduced fruitfulness. The vigorous growth produces dense leaf canopies which are characterized by senescing leaves, poor spray penetration, high relative humidity and long drying times. Diseases flourish in such canopies. Fruit developing in these shaded canopies is of poor quality because of high potassium levels, must pH and malic acid concentration.
Pre-planting decisions: The nature of the site and soil will effectively determine the vigor potential of the vineyard. Depth, texture, aeration, water holding capacity and pH of the soil will largely determine the size of the root system and, for unirrigated vineyards, the water supply. The vineyardist should consider these site effects when making decisions about rootstock and vine spacing in an attempt to modify the potential vigor of the site in a desirable direction. (see)
Post-planting decisions: Once the vineyard is planted, the grower still makes many annual decisions which influence vine vigor. These include fertilization, especially nitrogen fertilization, choice of vineyard floor management program, pruning and cropping level, and training system. If all of these decsions have been made wisely, then little more will need to be done. However in the real world optimal vine growth is rare, and often corrective practices, such as summer pruning or leaf removal, will improve the vine canopy formed in response to the par-ticular set of cultural practices used in a given vineyard.
The typical soil profile of a Long Island vineyard is 12 inches of silty/loam topsoil which has developed from the native sand. The sand comprises the subsoil. Because the topsoil is very easily eroded, soil landscape has had a profound effect on topsoil depth. The topsoil tends to wah down to lower parts of the vineyard. Thus a single vineyard row may have level sections with moderate topsoil depth and moderate water holding capacity. It may also have eroded sections where the topsoil is gone and only the sandy sub-soil is left which has very low water holding capacity. Finally there may be a low area where topsoil has collected and where the water supply is always plentiful. The result is shown above. These are actual vine growth data along two adjacent vineyards rows. There is little crop in the shallow sections and almost no crop in the deep sections. The very large and late growing vines kill to the ground almost every winter. Fortunately, the most of the vineyard has moderate soil depth.
Soil pH - remember that vinifera scions do not confer an ability for roots to tolerate aluminum ions in acid soils the way that native grape varieties do. Currently no rootstocks are known to resist low soil pH, but some will help ensure a balanced supply of mineral nutrients in high pH soils (for more see)
After selecting the site and preparing the soil, the most important pre-plant decision which will affect vine vigor is row and vine spacing. It is also the most misunderstood. There is a belief that increasing vine density (number of vines per acre) will cause a large reduction in vine vigor. The most common reason for this belief is the comparatively high vine densities common to European viticulture. Unfortunately, this is a half truth.
Helen Fisher is viticulturist for the Province of Ontario, Canada (and faculty member of Geulph University). This figure presents grapevine growth data that was part of her Cornell PhD thesis which investigated the question of vine spacing and vigor. She confirmed that increasing vine density decreases vine vigor in the sense that cane pruning weight per vine was reduced. However, when vine vigor is expressed as weight of cane prunings per foot of canopy, a reduction was only obtained by decreasing between row spacing. With wide rows, increasing vine spacing had no impact on vigor, and with narrow rows, increasing vine density actually increased vine vigor.
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Vine Cane Pruning Weights for Chardonnay Vines Growing at Geneva, NY Vines were planted in rows 9 feet apart and various in-row distances |
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| Cane Prunings pounds per | |||
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In-row planting distance (feet) |
Vine | Foot of Row | Acre |
| 4 | 1.7 | 0.43 | 2,075 |
| 6 | 2.0 | 0.33 | 1,614 |
| 8 | 2.4 | 0.29 | 1,423 |
| Significance Linear Quadratic |
0.0001 0.0001 |
0.0001 0.05 |
0.0001 0.01 |
Table 2 shows the effect of in-row vine spacing on Chardonnay vigor. It demonstrates that, as within-the-row spacing decreases, pruning weight per vine decreases, but does not decrease as fast as vine density increases. Hence, close in-the-row spacing tends to increase effective vine vigor (prunings/foot of row or per acre). These data suggest that we should examine the potential for decreased between row spacing and increased, not decreased, within-the-row spacing if our goal is to reduce vine canopy density and effective vine vigor.
Frequently growers withhold fertilizer in an attempt to reduce vine vigor. However, any practice which reduces the fundamental health of a vineyard will result in increased winter injury. This includes unbalanced nutritional status. The low pH soil disorder of vinifera cited above is especially associated with poor winter survival.
Commonly growers are afraid to supply vinifera vines with sufficient nitrogen in the belief that any stimulation will result in poor wood maturity and increased winter injury. Dr. Tony Wolf, the viticulturist for Virginia State University, studied the interaction between rootstock, nitrogen fertilization and Chardonnay performance in the Finger Lakes region of New York during his doctoral research. He showed that, when Chardonnay was grafted to a phyloxera and lime resistant rootstock (C. 3309) applying up to 75 lbs of N annually did no measurable harm to vine productivity or winter cold tolerance. With a non- lime resistant rootstock, Elvira, failure to add supplemental nitrogen reduced yield and quality. Reducing nitrogen additions did more harm than good.
Because New York vinifera vineyards should have a slope sufficient to ensure good air and surface water drainage, they are susceptible to soil erosion. As a result many are sown to permanent between-the-row sod. This is a desirable practice so long as soil depth and water holding capacity are sufficient to supply the needs of both the vine and the cover crop. However when vine size is inadequate, an alternative practice should be used. Floor management is detailed in other grape fact pages.,
No weeds should be allowed to develop under the vines. Because of the practice of hilling earth over the graft union as a means of winter protectio, in-the-row weed control for most NY vinifera vineyards is by mechanical or a combination of mechanical and chemical methods. Some growers hill-up on a semi-annual basis, and use only chemical weed control in the alternate years. Hills must be removed at least semi-annually or scion roots will develop which greatly de-vigorate the vine.
Again, the there is a widespread fear that vinifera vines are so fragile that they must be pampered in order to survive in a region with cold winters, has dominated the way the vines are pruned and cropped. In terms of disease control it is probably true that more is better, but with fertilization or cropping levels, excessive concern can cause the very problem the grower is trying to avoid. Severe pruning or thinning to reduce crop below its vine capacity will increase vigor and the likelihood of winter injury.
These data are from a pruning/thinning experiment on Chardonnay vines growing at Geneva. Actual pruning levels used in the experiment were 26, 52 or 78 shoots/vine at an eight foot in-the-row planting space or balance pruning using a formula of 20 shoots per pound of cane prunings. Half of the vines were thinned to one flower cluster per vine or not thinned at all. Note that, within a thinning category, smaller crops result in increased bud cold hardiness (lower median low temperature exotherm (LTE) temperature), but also that increased vine vigor (cane pruning/foot of row) is associated with less, not more cold hardiness, and the higher crop levels in the unthinned vines produced buds with lower freezing pints. In each plot the thinned, 26 shoots/vine treatment does not match up well with other treatments. That is because the severe pruning induces very vigorous shoot growth, but 26 shoots do not produce enough growth to make comparable cane pruning weight data.
In most years there has been not difference in fruit maturity between the different treatments. Taste panels rated wines made from the low crop vines to be inferior to those from high crops vines.
In regards vigor control, we have seen little difference between non-divided training systems. However, canopy division as with lyre or Geneva Double Curtain training can be a very useful technique to better display the foliage and reduce effective vigor (wt. of cane pruning per foot of canopy, rather than row).
| Effect of training system of vigor, yield and maturity of White Riesling grapes | ||||
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| Training System | Cane Prunings/Vine (lb.) | Cane Prunings/Ft. of canopy (lb) | Tons/Acre | Brix |
| Pendlebogen* | 3.4 b | 0.4 a | 5.2 b | 18.8 ab |
| Umbrella | 3.6 b | 0.5 a | 5.4 b | 18.8 ab |
| Fan | 3.6 b | 0.5 a | 5.8 ab | 17.9 b |
| Low Cordon* | 4.3 ab | 0.5 a | 6.9 a | 19.1 a |
| Lyre* | 5.1 a | 0.3 b | 6.9 a | 19.1 a |
* These are forms of vertical shoot positioned (VSP) training systems. The others have high or difuse heads.
The data in the above table emplify the benefits of canopy division for large vines. Note that in terms of vine vigor, there is little difference between the non-divided training systems, but that vine size (cane prunings/vine) is greatest with the divided canopy Lyre training. However if vine vigor is expressed on a foot of canopy basis, the divided canopy has a lower and more desirable value. Fruit from Lyre trained vines also had highest maturity and lowest rate of botrytis bunch rot.
The first and still most popular divided training system was Geneva Double Curtain (GDC) which is an aerial simulation of close row spacing in rows (vine trunks) which are widely spaced to accomodate standard US vineyard equipment. The high cordons allow tractors to pass under the vines. It was developed for Native American varieties which have a procumbent (trailing) growth habit. GDC is not suitable for cold tender varieties in New York because of the vulnerability of the extensive cordon system to winter injury.
Lyre training is an adaptation of GDC which uses low cordons (or less commonly canes) to produce two angled VSP canopies which accomodate tractors. The drawbacks of Lyre training are expensive trellis, difficult floor management, greater labor requirement and unsuitability for machine harvest. However, when preplant decisions have resulted in excessive vine vigor, yield and especially wine quality have greatly benefited from conversion.
Vertically divided training systems have been developed as an intermediate step between simple VSP and GDC or Lyre to reduce canopy density. The fundamental concept is that two thin canopies are produced on each vine. The canopies are stacked rather than separated horizontally. Cordon and cane systems have been developed. Currently the most popular versions are Scott Henry - which uses cane training. Half of the canopy is vertically shoot positioned up, and half is vertically shoot positioned down. Another version uses single or double cordons and is called Smart-Dyson. Growth from the upper cordon is positioned upward and growth from the lower cordon downward. A modification of both systems is done by eliminating the extensive and rigorous downward shoot positioning. This approach is termed ballerina. Positioning shoots in a downward direction reduces their vigor (rate and extent of shoot growth), and positioning shoots upward does the reverse. In New York we have had difficulty maintaining sufficient vigor in the downward pointing canopy to mature the fruit and wood. The lower canopy tends to die out. It remains to be seen if the use of the ballerina approach or careful cane selection can allow the system to be utilized for cold tender varieties in New York. (for further information on vine training system)
The cultural practices discussed above indirectly affect canopy
density by influencing growth potential (vine vigor). Shoot positioning,
summer pruning, shoot thinning and leaf removal directly affect
the canopy. With some training systems shoot positioning or summer
pruning may almost be mandatory, but in general, these are corrective
actions that must be taken when the other viticultural decisions
have not lead to an optimum vine size and hence canopy structure.
As corrective actions they can lead to dramatic improvements in
disease and fruit quality. However, they are expensive and will
only partially compensate for unbalanced vine vigor. Every grower
who has to depend upon these practices in order to obtain satisfactory
canopy structures should review all the viticultural management
options used to see if changing other practices might alter vine
growth so that the canopy does not require so much direct manipulation.
© Copyright 2000 Robert Pool
