Pruning Philosophy

Introduction: Pruning is arguably the most important cultural practice a grape grower does. Grapevines are pruned to regulate the amount of fruit they produce each year. Without pruning, yes the vines would produce fruit, and that fruit can successfully help the plant continue its genetic journey. But such fruit rarely achieves the amount and quality to support a consistent economic return to a grower.  
    Pruning has an overall dwarfing or depressing effect on the vine. that is, pruned vines are made physically smaller while the vigor of remaining growing points is increased. When wood or top growth is removed, the roots that previously supported the above ground growth will have an abundance of hormones and carbohydrate reserves and a greater water and mineral absorbance capacity relative to the remaining top growth. This excessive supply of water and minerals stimulates the remaining shoots to grow expand at a rapid rate. The rate of growth over time is referred to as "vigor". Vigor should not be confused with the total amount of growth or overall vine size. To summarize: pruned vines are physically smaller than unpruned vines and remaining shoots are more vigorous compared to shoots on unpruned vines.
    The descriptor "vine capacity" is often confused with vigor. Vine capacity relates to vine size, and is a separate concept. Capacity is the total amount of fruit or crop a given vine can support to a desired degree of maturity. Vine productivity and sustainability depends on vine capacity. First, capacity dictates the vines's physiological requirements and secondly it impacts the economic viability of the vineyard as enterprise. When you prune, you determine:
        1. type and position of fruitful buds
        2. bud number: which impacts crop load, berry composition: % sugar, acid content, pH, flavor, aroma and color compounds that determine fruit 'quality'   

Purpose of pruning: to achieve the desired amount and quality of fruit over a number of years.
        1. Set the appropriate fruit load to the vine's size and capacity, accomplished by leaving an appropriate number of buds on the vine at pruning.
        2. Shape and training the vine to a given trellis system. Vine growth is directed into a well-spaced canopy to allow air, sunlight and spray materials into the canopy. The goal is to ensure the optimum amount of sunlight strikes foliage and fruit at the optimum time over the course of the day and growing season. A successful grape grower is simultaneously mindful of the current and subsequent seasons when considering pruning and training tasks.  

Balanced pruning: How many buds to leave?
    Weigh all one-year old wood that is pruned off the vine. Count the remaining buds. Leave 30 buds for the first lb. of wood removed and another 10 buds for every lb. over the first pound. This, ‘30+10’ formula was developed for American varieties of Vitis labrusca, such as Concord, Himrod, Glenora, Niagara, Suffolk Red, etc. For Vitis vinifera or European wine grape cultivars: Chardonnay, Cabernet Sauvignon etc., begin with 20 buds per 1 lb. of wood removed or a 20 + 20 system. These ‘formulas’ are intended as a starting place and are not definitive. They help match bud numbers and subsequent leaf area to the crop it must support. Balanced pruning uses:
        1. cane weight, only one-year wood is weighed
        2. bud or nodes counted and left on the vine 
        3. begins with a pruning formula for estimating vine capacity to match buds to leaf area
    Dr. Nelson Shaulis, of Cornell University, utilized this technique in the middle of the 20th century to help grape growers determine the number of nodes or “buds” to retain at pruning. The process assumes the selection of well-exposed canes with fruitful buds. Pruning formulas are driven by growth and fruiting characteristics of the variety and their environment. Vine capacity varies between trellis/training systems and between adjoining vines in a row. The goal is to avoid over or under-pruning vines of differing capacities. Balanced pruning is a first step in achieving the annual desired quality level while maintaining or improving vine capacity for the following years’ crops (Coombe and Dry, 1992). 

Example bud number formulas:

Variety Formula                    Variety                     Formula                                                 

Cabernet Sauvignon 20+20 Concord                   30+10

Cabernet Franc         20+20 Niagara                    40+10

Chardonnay         20+20 Vidal (hybrid)          15+10

Riesling                 20+20 Seyval (hybrid)          5+10

Other hybrids            20+10

A measure of vine capacity: leaf area : fruit ratio 
    The leaf area to fruit ratio is defined as: Pn (photosynthetically active) leaf area measured in square centimeters (cm2) to mass of fruit measured in grams (g). This ratio depends on the trellis system used. The vertical shoot positioned (VSP) trellis generates a leaf area : fruit ratio of about 0.8 to 1.2 m2 leaf area per kg fruit or about 10 cm2 of leaf area per 2 g of fruit, about 5-6 mature leaves per each medium sized cluster. Divided canopies can be a bit more efficient, where only 0.5 to 0.8 m2/kg are needed to mature fruit (Figure 1). 

Figure 1. Above left:The relationship of leaf area to crop weight. Below right: Examples of three trellis systems: A1 = vertical, B1 = lyre and C1 = Geneva double curtain, (Kliewer and Dokoozlian, 2005). 

1. Example: Assume the European winegrape, V. vinifera, vine you have pruned produced 3.5 lb. of pruning wood. Applying the 20+20 formula would result in 20 nodes left for the first pound of canes, plus an additional 20 nodes for each pound above the first. Thus, the 3.5 pound of wood would indicate to leave 70 buds or nodes on the vine. However, in practice, if the vines occupy 6 ft of trellis, and it is recommended to leave 6 buds/ft., or 2-3 spurs per foot, this would result in ~ 42 buds on the vine not the 70 indicated by the formula. The bud number per foot of cordon/trellis is more important than the total number of buds per vine because to leave more would result in a very dense, shaded canopy. Remember, a vine canopy with well-spaced shoots, leaves, and clusters is desired. Prune to avoid a crowded, dense canopy that increases disease and insect pressure, and has poor light exposure of leaves and fruit clusters. 

2. Wood : fruit ratio should be approximately 5-6 or 5-6 lb. of fruit per 1 lb. of wood removed. In other words, a vine that produces 2 lb. of pruned one-year old wood is likely capable of supporting 10 to 12 lb. of fruit the following season.

Factors that impact pruning…or, pruning depends on:
    Climate: Is your climate continental or maritime? New Mexico has a continental climate with a high likelihood of winter and/or frost injury due to wide swings between night and day temperatures (diurnal range). There is little to no dampening effect from humidity or large bodies of water. In this case:
        1. Leave more buds at pruning time and be prepared to shoot/crop thin later in the season.
        2. Prune late, this will delay budburst and possibly avoid frost injury in the spring.
        3. Consider “kicker canes”. These are ‘extra’ canes left on the vine. Kicker canes can enter budburst relatively late and can replace buds killed by frost. If kicker canes are not used, they are typically replaced each year. Kicker canes can reduce or mitigate excessive vine vigor or be positioned and used as a replacement trunk. 
    Soil Fertility: 
        1. deep soil = vigorous growth, prune lightly (leave more buds) to decrease rate of early shoot growth
        2. poor soil = prune severely (leave fewer buds), to stimulate vigor in remaining buds
    Variety: dictates: bunches/shoot, flowers/cluster, berry weight, and bud position.
        1. Some varieties have basal buds that are seldom fruitful, example: Nebbiolo and Thompson Seedless.
        2. Other varieties have basal buds not counted at pruning time, that can burst and grow
            later leading to a congested canopy. 
        3. Apical dominance? This phenomenon is most evident in the spring. Buds at cane tips break bud first and subsequently, buds located below the 'top' (proximal to the base of cane) will break bud later. The grape grower can take advantage of this natural tendency by leaving longer spurs at the initial pruning pass. After the apical buds begin to grow, one then prunes them off. This removal of the apical growing buds will delay bud break in the remaining buds and their emergence later can help avoid damage due to late frost events.    
     Economic: Winter pruning is the most economical way to control crop, but it is not very precise. Cluster, fruit and shoot thinning during the growing season costs more, but is more precise, compared to winter or dormant pruning. 

Pruning Procedures 
1. Timing: Vines can be pruned anytime between leaf fall and bud break the following spring. Although early pruned vines can be more susceptible to winter injury. The earlier vines are pruned, the earlier they will break bud in the spring, and depending on timing, will be more likely to be damaged due to late frosts. When to begin pruning is dictated by size of vineyard and number of pruners available. Pruning should be completed by budburst. Experienced pruners can typically cane prune an acre of vines in 30 to 40 hours. Pruning after budburst increases risk of bud damage, because the tender buds can be damaged or knocked off.  
Early pruning = early bud break, growth advancement can persist through harvest
Double pruning = Make two passes through the vineyard. 
--First pass: make rough cuts and remove the pruned wood from the trellis
--Second pass: adjust bud numbers to desired number/vine prior to bud break
Delayed pruning: pruning near budburst will delay development of remaining buds 
--The delay in growth can persist through harvest
--Delayed pruning until after apical shoots are well emerged and growing can reduce yields     somewhat. This can be used to advantage in reduction of the amount of required cluster         thinning later in the growing season.
--Vines ‘bleeding’ sap will not be injured by spring pruning…but young buds can be knocked off by pruning and wood removal. Therefore, all pruned or unwanted wood should be removed from the trellis before the bud swell. 
--Delayed pruning can reduce eutypa, esca, botryosphaeria and other wood rotting diseases (Figure 2).

Figure 2. Left: a cross section of a cordon infected with fungal wood rotting disease, evident in the discoloration. Right: end-cut cordon revealing fungal wood rotting infection. 

2.  Pruning Degree:
--Balanced pruning: buds retained are based on weight of wood removed at annual dormant pruning
SEVERE              < 20 buds left on the vine 
MODERATE             20 to 70 buds left on vine
LIGHT             > 75 buds left on the vine 
 
3.  Cane Selection Criteria:
--Varietal color: light brown V. vinifera varieties, with brown coloration to the cane tip,
V. labrusca cultivars have a reddish-brown color
--1 cm (3/8 inch) in diameter, strive for cane uniformity
-- moderate internode length, about 3-4 inches
-- canes of different length and diameter should retain different number of buds
-- age or location of canes and spurs is dependent on training and trellis system 
4. Vine Age: Use different training goals for different age vines. 
-- young vines – establishment of framework based on trunk arrangement
-- mature vines – framework and bud type placement within trellis system


    Pruning affects most vineyard activities and vine growth parameters such as: crop yield, winter hardiness, insect and disease management and ultimately, berry composition and the resultant berry, juice and wine quality (Chapman et al., 2004). With practice, pruning can become intuitive. A grape grower with an eye towards a long-lived vineyard should maintain good records to supplement and support her pruning decisions. 


REFERENCES
1. Chapman, D.M., Matthews, M.A., and J.X. Guinard. 2004. Sensory attributes of Cabernet
        Sauvignon wines made from vines with different crop yields. Am. J. Enol. Vitic. 55: 325-334.
2. Coombe, B.G., and P.R. Dry. 1992. in,Viticulture Volume 2, Practices. Winetitles. Adelaide, Australia
3. Kliewer, W. M. and N. Dokoozlian. 2005. Leaf area/crop weight ratios of grapevines: influence on
        fruit composition and wine quality. Am. J. Enol. Vitic. 56:170-181.
4. Skinkis, P.A. and A.Vance. 2013. Understanding Vine Balance, an important concept in vineyard
        management https://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/39883/EM%209068.pdf
5. Winkler, A.J., Cook, J.A., Kliewer, W.M., and L.A. Lider. 1974. in, General Viticulture. University of
        California Press, Berkeley.
6. Reynolds, A.G. and T.K. Wolf. 2008. Pruning and Training, 98 -123, in, Wine Grape Production
        Guide for Eastern North America. T.K. Wolf, ed. Natural Resource, Agriculture and Engineering
        Service (NRAES) Cooperative Extension, Ithaca, NY. 
7. General information on pruning and other grape growing techniques and tools:
        eViticulture http://eViticulture.org