Keynote paper

Canopy management: identifying the problems and practical solutions

Richard E. Smart and Steve M. Smith Scientist, Viticulture and Technician, Viticulture MAFTech Ruakura Agriculture Centre Private Bag, Hamilton, New Zealand

Abstract This paper discusses the implications for yield and qual-

ity of excessively dense canopies. Simple techniques are presented to identify problem canopies including measure-ments of canopy surface area, visual assessment of cano-pies, point quadrat measurements, leaf area measurement and measurements at winter pruning. Results are presented to show how problem canopies can be overcome, with emphasis on shoot devigouration by pruning level and training system. The economic advantages of some new training systems are presented.

Introduction Canopy management consists of deliberate decisions by

the viticulturist to achieve some desirable canopy configu-ration, be it in terms of surface area, volume, leaf area per shoot, fruit exposure, shoot orientation or even vine phys-iological status. Important to consider are the economic costs and benefits of "canopy management". Management includes concepts of problem identification and then their solution. I have observed (Smart 1987a) that many canopy components are "under-managed"— for example shoot orientation in Australian and Californian vineyards, where shoot position is determined by the natural forces of gravity and wind rather than the viticulturists intervention.

Canopy management is being increasingly recognised as an important tool for manipulating wine grape yield and quality (Smart 1985a). This is not to suggest that canopy management is the only factor to be considered in improv-ing wine quality. Planting with a high-health, genetically superior clone of the appropriate cultivar grafted to an appropriate rootstock and matched to a suitable climate is of paramount importance. Soil conditions are acknowledged also of being of considerable significance, particularly in interaction with the climate and manage-ment systems in regulation of water and mineral status. Also important are timeliness of harvest, fruit protection and of course appropriate vinification and conservation.

This paper will indicate the viticultural and oenological implications of improper canopy management, how problem canopies can be identified, and some practical and economic techniques of canopy management. The concept of vineyard quality assurance will be introduced whereby using simple assessments the viticulturist is able to moni-tor progress in canopy management.

The effects of improper canopy management Shade depresses fruit bud initiation as is shown by recent

reviews (Kliewer 1982; Shaulis 1982) so that training sys-tems which reduce within-canopy shade lead to increased yield. Bunch rot incidence is also increased by dense cano-pies (Rotem and Palti 1969) and perhaps many of the effects noted of pruning level, rootstock and fertilisation may be indirect effects through canopy microclimate. Shade effects on fruit composition are increasingly being acknowledged, and a recent review (Smart 1985a) indicates that shade causes inferior fruit composition. For example, shade causes increased pH and K and malic acid concen-tration, and reduced sugar, anthocyanin, phenol and fruit flavour concentrations. Light quality as well as light quan-tity effects have recently been implicated as affecting grape-vine physiology, especially fruit ripening (Smart 1987b; Smart 1987c).

Improper canopy management can cause increased production costs also. For example, vines with long, heavy canes can be more expensive to hand prune, and dense canopies can cause inefficiencies of spray application. Fur-ther, modern canopy design aims to enhance mechanisa-tion, especially for summer trimming and winter pruning along with fruit harvesting. Operations such as leaf pluck-ing in the fruit zone are facilitated by orderly arrangement of shoots in the canopy.

The appropriate management of dense shaded canopies is a major problem facing modern viticulture. In fact the problem now is of higher incidence than ever before, due to advances in virus elimination, fertilisation, irrigation, plant protection and weed control. In the past, inadequate cultural methods caused devigouration and canopies were often less dense. These problems are exacerbated in many New World viticultural regions due to choice of excessively deep or fertile soils for vineyards. Such is commonly the case in New Zealand.

Identifying problem canopies Canopy surface area determination

Canopy surface area can be determined by sketching the canopy end-section to scale and calculating the exposed surface area. Surfaces facing downwards are not included, though this ruling is recognised as somewhat arbitrary (Smart 1985a). Similarly, there is a small effect of row orientation which is ignored. Fig. 1 lists five sample canopy

gib Proceedings Second international Cool Climate Viticulture and Oenology Symposium, Auckland, New Zealand. January 1988.

Row spacing •1m Canopy SA•I9,000 m2/ha

x/h•088

Row spacing • 2m I Canopy SA •18,000 m2/ha x/h .1 00

Row spacing ■ 3m Canopy SA • I2,330 m 2/ha x/hal.56

Row spacing • 3 m Canopy SA 223,330 m 2/ha x/h• 0.5

I RT2T" Row spacing • 3.6m Canopy SA • 21,110 m 2/ha x/h • 100

Canopy management identifying problems ono solutions

cross-sections and canopy surface area calculations for row spacings 1-3.6 m, and for divided and undivided canopies. Dimensions for the first four trellises are given by Smart (1985a). These are: Bordeaux traditional, row spacing 1 m; Intermediate row spacing 2 m; Traditional (New Zealand), row spacing 3m; and "U" or "Lyre" trellis with row spacing 3 m. The fifth design is the Ruakura Twin Two Tier (RT2T), 3.6 m row spacing. It is a horizontally and vertically divided trellis under evaluation at Rukuhia Horticultural Research Station, New Zealand (Smart 1987a).

Fig. 1. Vineyard cross sections drawn to scale, and calculated canopy sur-

face area and ratio x/h (see text).

The small canopy surface area of traditional, undivided canopies is apparent, a primary cause of canopy shading. Sunlight interception will be proportional to this value. Canopy surface area is increased by decreasing row spac-ing, or by canopy division as for the "U" and "RT2T". The ratio of distance between canopies (x) to their height (h) is important. Smart (1985b) has suggested that when this value is less than 1.0 then shading at the base of canopy walls may be excessive. For this reason, the value of canopy surface area for the RT2T (21, 110 m 2/ha) is at about the maximum value possible.

Visual assessment of canopies Canopy gaps, canopy density and fruit exposure can be

readily visually estimated. This leads to the concept of a "vineyard scorecard" first developed in South Australia in 1981 (Smart et al., 1985). With sufficient instruction and experience, scorers can give similar answers. Estimates of canopy density can be incorporated with other visual esti-mates of physiological significance to make an assessment of the potential winegrape quality from the vineyard. The

scorecard has been modified over several years, and the MKIV version has eight characters each worth 10 points to be assessed, just before harvest. These are: canopy gaps, leaf size, leaf colour, canopy density, fruit exposure, shoot length, lateral growth, and growing shoot tip presence. Table 1 shows the MKIV scorecard, with each parameter assessed out of 10 points, for a total of 80. High scoring canopies have adequate canopy gaps, slightly small leaves, dull but green healthy leaves, low leaf layer number, high fruit exposure, intermediate shoot length, limited or zero lateral growth and no growing shoot tips. This scorecard is being used to evaluate experimental and commercial vine-yards, and is proving a useful tool to determine manage-ment strategies.

Point quadrat assessment This technique uses a long (ca. 1 m) thin (ca. 3 mm)

straight, sharpened metal rod inserted through the canopy to record "contact" with canopy components (fruit and leaves— shoots can generally be ignored). For vertical cano-pies, the rod is inserted horizontally in the fruit zone. For non-vertical canopies, the rod is inserted at an angle (say 45-600) towards the fruit zone. By recording contacts as the rod progresses, and with a sample of say 100 insertions per canopy, the following can be readily calculated:

Percent gaps—number of insertions with no contact/100.

Leaf layer number (LLN)— total number of leaf con-tacts for all insertions/100.

Percent interior fruit—number of contacts with fruit not at the canopy exterior divided by total number of fruit contacts.

Percent interior leaves— number of contacts with leaves not at the canopy exterior divided by total number of leaf contacts.

These measurements and calculations can be readily made, and provided sampling is adequate can accurately describe canopies.

Fig. 2 shows the results of assessing five experimental Cabernet Franc canopies at Rukuhia. The higher LLN of standard vines was associated with lower canopy gaps, and higher proportions of interior leaves and clusters. The con-verse was true for RT2T vines with the low mean LLN of 0.73. Note that the proportion of interior fruit is about twice that of interior leaves, due to the fact that leaves are able to adjust their position to optimise illumination and clusters cannot (Smart et al., 1982).

Leaf area assessment Shoot leaf area can be readily calculated by comparing

the fresh weight of a known number of discs of known area (cut with a cork borer) to the fresh weight of leaves. Leaf area can also be measured with electronic meters and by correlations with length measurements. It is instructive to separate main and lateral leaves, and also to record shoot length. Sufficient shoots need be sampled to obtain a meaningful average. Leaf area per. vine can be calculated by multiplying with the average shoot number per vine. The ratio of leaf area to canopy surface area (LA/SA) can be then determined. Ideal values of this figure should be 1.2 or lower (Smart 1984); note that for tall thin canopies LLNZ 2 x LA/SA.

110 Proceedings Second International Cool Climate Viticulture ona Oenology Symposium. Auckland. New Z,

Canopy management identifying problems and solutions

Table 1. Ruakura vineyard ernrecard (MK IV).

This scorecard should be used just before harvest. NB: If majority of shoots are less than 30 cm long, or if these vines are clearly diseased, or chlorotic or necrotic, or excesively stressed, DO NOT SCORE VINEYARD.

A. Assessed standing away from canopy

1. CANOPY GAPS (from side to side of canopy, within area contained by 90% of canopy boundary) score:

5. FRUIT EXPOSURE (remember that the canopy has two sides normally: that fruit which is not exposed

• < 40°/s 10 on your side may be exposed to • about 50°/s 8 the other side score: • about 30°/s 6 • about 60 07o or more exposed 10

• about 20°/s 4 • about 50% 8 • about 10 070 or less 0 • about 40°/s 6

• about 30% 4 2. LEAF SIZE (basal-mid leaves on

shoot, exterior). For this variety are the leaves: 7.

• about 20% or less

LATERAL GROWTH (normally from

2

• slightly small 10 about point where shoots trimmed. • average 8 If laterals have been trimmed, • slightly large 6 look at diameter of stubs) • very large 2 • limited or zero lateral growth 10 • very small 2 • moderate vigour lateral growth 6

• very vigorous growth 2 3. LEAF COLOUR (basal-mid exterior

leaves, in fruit zone) 8. GROWING TIPS (of all shoots, the • leaves green, healthy,

slightly pale, dull 10 proportion with actively growing

tips - make due allowances for • leaves dark green, shiny,

healthy 6 recent trimming)

about 5elo or less 10 • leaves yellowish green, healthy 6 • about 10% 8 • leaves with mild nutrient 6 • about 20% 6

deficiency symptoms • about 30% 4 • unhealthy leaves, with marked 2 • about 40% 2

necrosis or chlorosis • about 50 07o or more 0

B. Assessed standing at canopy Total point score /80

4. CANOPY DENSITY (from side to side, in fruit zone), mean leaf layer number (LLN)

• about 1 or less 10 • about 1.5 8 • about 2 4 • more than 2 2

Similarly the shoot descriptor gamma (X, the ratio of leaf area/shoot length, units cm) can be derived from the above measurements. This can then lead to calculations of desira-ble shoot spacing, using relations developed by Smart (1985a), Smart et al., (1987). For uniform vertical shoots arising along a line and D cm apart, with leaves inclined at a mean angle 8 to the horizon, then

LLN sin 8/1) (1) For an optimal LLN of 1.5 (Smart 1987a), and for meas-

ured values of gamma and , the optimal shoot spacing can be calculated.

Winter pruning assessments During winter pruning the number of shoots growing

the previous season can be counted, and pruning weight of 1 year old wood determined. Then by division the mean shoot weight can be calculated. These three parameters (shoot number, pruning weight, mean shoot weight) can be used to indirectly assess canopy microclimate. Unpub-lished studies by the author suggest an optimal spacing for moderate vigour and verticially trained Gewurztraminer shoots to be about 15 shoots/m; more vigorous shoots need

to be more widely spaced, and less vigorous shoots can be more closely spaced, to produce a desirable LLN of 1.5. Pruning weights in excess of 1.0 kg/m cordon length have previously been associated with excessively dense canopies (May 1973) but recent studies have suggested that this figure should be 0.5 kg/m or less for trimmed Gewurztraminer and Cabernet Franc canopies (Smart, unpublished data) to retain optimal canopy microclimate. Whether shoots are trimmed or not, and whether shoots are vertically displayed or not will affect this critical value.

Data from a study with the cultivar Shiraz in Australia (Smart 1982) have shown a correlation of pruning weight and vine leaf area with 1 kg pruning weight approximately equivalent to 10 m 2 leaf area. Recent studies with the cul-tivar Cabernet Franc show a ratio of 5-10 m 2/kg.

The pruning weight data can be combined with yield measurements of the previous vintage to provide a ratio of yield/pruning weight. Bravdo et al., (1984) have recently shown that values of the ratio of yield to pruning weight in excess of 10 is an indication of "overcropping"— that is a vine condition where there is insufficient exposed leaf area to adequately ripen the fruit. A yield/pruning weiolimr

Proceedings Second International Cool Climate Viticulture and Oenology Symposium, Auckland, New Zealand. January 1988.

Canopy management: identifying problems and solutions

40

20 1

Canopy gaps • j

I L x V• •14 x

.AA x X 0

or 0 0 o 40

20

Interior leaves

x x x

0

0 o0

oo

0 0 100 - Interior fruit

! 80-u_

60- • a

0

8

0 0

TK3T • 40- a _

is"° x L .66

x TK2T a TAT x

20 - II -A RT2T STD 0

Fig. 2. The relationship between LLN and fruit and leaf exposure assessed by point quadrat. Cabernet Franc, Rukubia, 1987.

ratio of 10 corresponds to a leaf area/fruit weight ratio of 10 cm 2/g fruit fresh weight (for 1 kg pruning weight:v., 10 m2 leaf area) considered appropriate to effectively ripen grapes (Shaulis and Smart 1974). We find a yield/pruning weight ratio of 8.5 about ideal for Cabernet Franc.

Mean shoot weight is a useful indicator of adequacy or excess of vegetative growth. High values of mean shoot weight can indicate excessively long (say more than 12-15 nodes), excessively thick stems (say more than 10 mm diameter) or excessively leafy shoots with large main leaves and excessive lateral growth. Mean shoot weight is a bet-ter indicator than pruning weight since lightly pruned vines can have high pruning weights though made up of large numbers of individually smaller shoots (Clingeleffer and Possingham 1987; Soderlund et al., 1987).

We find for Cabernet Franc for example that a mean shoot weight of 20-30 g corresponds to a desirable shoot vigour level and a well balanced vine, but that vines severely pruned and on the restrictive standard trellis have mean shoot weight of 70 g.

Vine development and fruit composition Excessively dense canopies can lead to susceptibility to

bunch rot and delayed maturity, i.e. lower sugar, higher pH, malate and K. Associated with ripening delays is a delay in development of woody tissue (periderm) on the grapevine shoots after veraison.

Overcoming problem canopies Shoot positioning

Where canopies are not shoot positioned, as is com-monly the case in Australia and California, canopies can have a large surface area although often also considerable within canopy shading. Converting such canopies to ver-tically upwards shoot positioning may in fact reduce canopy surface area and increase shading (Smart 1987a). In New Zealand, we have recorded modest yield and sugar con-centration gains by increasing canopy surface area with the Scott-Henry (or Smart-Henry) form of trellis conversion (Smart 1987a). With this system shoots from the bottom cane are trained downwards to fill the gap which normally exists when all shoots are trained upwards. Then shoot den-sity is effectively halved, and canopy surface area is almost doubled.

Leaf plucking Papers to be presented elsewhere in this symposium by

Kliewer et al. and Smith et al. highlight the benefits to be had from timely leaf removal in the cluster zone. So long as leaf removal is not so extensive as to reduce the leaf/fruit ratio below the critical level then this practice is effective in increasing fruit exposure in otherwise "too dense" canopies.

Shoot devigouration and pruning level Modern vineyards often have excessively leafy shoots for

reasons outlined in the Introduction. Lower vigour shoots have smaller main leaves and fewer and smaller lateral leaves. However, such shoots do not necessarily have lower yield and lower vigour shoots can be more closely spaced to allow for high yielding vineyards yet without shaded microclimates. Other papers presented at this symposium detail soil effects and cover crop effects on shoot devigou-ration. There is a well acknowledged effect of water defic': on shoot growth (Smart and Coombe 1983) and generally soil and cover crop effects can be explained primarily by effects on vine water supply.

A multitude of pruning trials around the world have shown that light pruning is effective in shoot devigoura-tion. Recently these concepts have been further extended by the development of "mechanical" then "minimal" prun-ing especially in Australia. Recent studies (Clingeleffer and Possingham 1987) have shown that minimal pruning leads to production of larger canopy surface area, especially early in the growing season, from a larger number of smaller shoots. For example normal pruned Sultana vines had 77 shoots per vine compared to 276 for minimal pruned, with respective mean shoot weights of 31 and 3 g.

Fig. 3 presents results of a pruning trial with the cul:i-var Shiraz in the hot climate of Griffith, N.S.W. conducted during the 1969-70 growing season. Vines were 6 years old, spaced 3.8 x 2.5 m and previously spur'pruned to 50 two-node bearers. Four treatments were imposed: pruning to 50 nodes (buds), 150 nodes, 300 nodes or unpruned (about 1200 nodes retained). Yield increased with pruning level up to 300 nodes retained per vine, and sugar concentra-tion declined slightly at high node numbers. The yield increase is due to more bunches although bunch weight decreased with more bunches per vine. Flower number per bunch was independent of pruning level, but set was reduced by light pruning: reduced berry weight.aad berry

• x oo

LLN

112 Proceedings Second International Cool Climate Viticulture and Oenology Symposium, Auckland, New Zealand

- 4

CO

• •-•-•

7/- -

0

, {0 200 400 1200

Nodes per vine Fig. 3. Yield, growth and fruit composition responses of Shiraz grape-vines to pruning level. Griffith, N.S.W., 1969-70

number both contributed to reduced bunch weight. Light pruning caused effective shoot devigouration, with shorter shoots, fewer main and lateral leaves and reduced mean leaf area.

This trial is indicative of vine response to a wide range of node numbers in a hot climate, and demonstrates that large node numbers per plant can lead to effective shoot devigouration without yield loss. Similar principles apply in cool climates, though fruit sugar levels are more likely to be depressed at high yields. A notable feature of this trial, and others like it, is that canopy surface area is not increased proportionally to node numbers retained. That is, node number per vine is varied while vine spacing, or more importantly canopy length (or area) per vine is cons-tant or nearly so. Hence large node and shoot numbers per vine are associated with increased canopy shading. The Cabernet Franc experiment at Rukuhia is examining the notion of using large node number per vine to devigourate shoots, but in turn making canopy length proportionally larger so that shoots are not crowded. In particular, the treatment RT2T involve vines with different cordon lengths and hence node numbers, but all at the same vine and node spacing. Effects of these treatments on shoot devigoura-tion are subsequently presented.

'training system Since the description of the Geneva Double Curtain

(GDC) trellis in 1966 by Shaulis and coworkers in the eastern United States there has been an upsurge of interest in using training systems for canopy management. Smart (1987a) outlines principles for training system design to improve yield and quality and to facilitate mechanisation. Canopy division can be effective in reducing within canopy

• 40 •

20

100

//—.1

100 50 o; 1 —EEo • C .1;

I

e rr. ••■••

C o • 4T, •-• o .0 g E

co C

4001

0 400

200-

0

20 -

10 -

[1.0

2000

"

•

647 1000 °

o o -J

o E o

"•`' I

C. 0 0

I CC1 • I

Canopy management: identifying problems ana solutions

shade, but canopy curtains should be far enough apart to ensure no mutual shading of each other (Smart 1985b). Canopy division typically promotes increases in yield and quality (Shaulis et al., 1966; Smart 1985a; Carbonneau et al., 1978; Carbonneau 1985). Some of the "new" training systems can be completely mechanised for summer and winter pruning and harvesting i.e. GDC (Baldini 1982); some, like the U system (Carbonneau et al., 1978) and the TUT (Smart 1985b) require some machine modification before widespread use, and some, like the Tatura trellis (Van den Ende 1984) will be difficult to totally mechanise.

Improvements to training system are a principal means of potentially overcoming canopy shade problems for many vineyards. Our recent research however indicates that sim-ple canopy division (say with 2 m canopy/m row length) may not be sufficient to • overcome shading. The "new generation" of trellis systems such as the RT2T, extensively divided with 4 m canopy/m row, and using wide vine spac-ings and large bud numbers per vine may be required on very fertile soils to achieve a desirable microclimate.

It has been apparent for Cabernet Franc at Rukuhia that training systems with large exposed leaf areas (i.e. Tatura, RT2T) use water more quickly than standard vines and thus water stress may be more readily induced, a considerable advantage when vineyards are grown in areas of high rain-fall and low evaporation. Carbonneau (1987) has recently demonstrated the significance of leaf:root ratio of differ-ent training systems in Bordeaux.

Table 2 summarises the results of the 1986-87 growing season for the Cabernet Franc trellis trial at Rukuhia. Effects of training system and node number on yield, fruit composition, shoot devigouration and canopy microclimate are presented. Row by vine spacing is 3.6 x 2 m. "Small" and large" vines trained to RT2T differed in cordon length and node number. Note that cordons were not fully estab-lished for Tatura and RT2T large vines, so potential yields in future will be greater.

Pruning weight per vine was relatively constant between treatments (3.5 to 4.8 kg/vine) but mean shoot weight was much reduced by vines with large bud numbers, from 69 g/shoot for standard vines to 23 g/shoot for Tatura. Due to restrictive cordon length, the yield of standard vines (11 t/ha) was considerably inferior to RT2T (29 t/ha) and Tatura (40 t/ha). Measurements of yield to pruning weight, and shoot leaf area and its components indicated the extent of shoot devigouration obtained by RT2T and Tatura sys-tems, and also by bud number per vine. The canopy microclimate of the standard was inferior to other systems with higher LLN, fewer gaps and higher proportions of interior leaves and fruit. While the Tatura trellis had wide shoot spacing, shoots from adjacent cordons were inter-mingled, and fruit tended to be located away from the upper canopy surface in the shade. This was implicated for example in the higher elo rot of fruit on the Tatura trellis at harvest.

There was little effect of training system on fruit com-position at harvest, the most notable being increased pH for standard trained vines.

Wine quality was assessed by experienced judges in August 1987 for 1986 and 1987 wines produced using stan-dard microvinification techniques. For both years, vines trained on the Tatura trellis produced the most preferred

)V° Proceedings Second International Cool Climate Viticulture and Oenology Symposium, Auckland. New Zealand. January 1988.

Canopy management . identifying problems and solutions

Table 2. Effect of training system and vine bud number on yield, growth, canopy microclimate, fruit composition and wine quality of Cabernet Franc 198647 growing season.

Standard "Small" vines

Training system

RT2T "Large"

vines Tatura LSD

Nodes per vine 47 83 154 238 8 Potential cordon

length/vine (m) 2 6 12 24 NA

Shoots per vine 54 96 156 207 11

Growth Pruning weight/vine (kg) 3.7 3.5 3.8 4.8 0.5 Mean shoot wt (g) 69 37 25 23 4 Yield/pruning ratio 2.0 4.9 7.4 6.0 NA Mean main leaf area (cm 2) 164 125 104 11 Lateral leaf area/shoot (cm 2 ) 1272 860 620 412 Total leaf area/shoot (cm 2) 3615 2443 2086 45 1 Leaf area/fruit wt (cm 2/g) 20.9 18.7 12.7 4.1

Microclimate Percent gaps 3.3 20.3 31.3 17.0 10.4 LLN 2.17 0.81 0.64 1.28 0.22 210 interior leaves 25 5 2 7 (41)' o interior fruit 71 13 4 21 (79)' 16

Shoots/m cordon 27 16 13 9

Yield Yield per vine (kg) 7.6 17.2 27.8 28.8 2.7 Yield (t/ha) 10.6 28.8b 28.8b 40.0 3.9 24 rot 2.5 1.3 0.8 4.7 2.9

Fruit composition (harvest) Sugar ( 0 13rix) 19.3 18.9 19.2 18.7 0.8 Titratable acidity (g/1) 8.6 8.4 8.1 8.5 0.7 pH 3.14 3.09 3.09 3.08 0.04 Mean berry wt (g) 1.58 1.60 1.70 1.41 0,14

Wine quality (score ex 20) 1986 vintage 13.1 14.0c 15.2 1.8 1987 vintage 13.7 12.8c 15.1 2.5

°Values in brackets are estimates obtained when fruit and clusters at the bottom canopy surface are not counted as "exterior"

°Since "large" and "small" vines are adjacent in one plot this yield is the

`Fruit from large and small vines combined.

wines, and in 1986 the standard trellis the least preferred. These results appear in contradiction with canopy tnicrocli, mate measurements presented-especially for the 1986-87 growing season, since a high proportion of fruit on the Tatura trellis was shaded. We believe the reason for the apparent superiority of the Tatura trellis in these 2 years is the fact that water stress was evident for these vines in both years, reducing active shoot growth and berry weight. This water loss was a result of the largest exposed leaf area of all treatments.

Vineyard economics Improved training systems require typically an increased

capital expenditure at planting, due to requirements for more wire, posts and/or crossarms. For close row spacing designs, there is an increased plant cost, especially signifi-cant when using grafted plants.

In general, the efficient viticulturist cannot afford not to make this initial capital investment as vineyard returns are significantly increased. This is due primarily to increased yield and hence return, though perhaps also for bonus payments for increased quality and in some instances increased adoption of machines.

In a recent comprehensive study of the economics of training systems Crawford (1987) has shown that cost of establishing a vineyard in New Zealand trained to the stan-dard trellis (3m x 1.5m) is NZ$3.55/m row or NZ$10,786/ha of which the costs of grafted plants and

equivalent of mean plot yield, with two small vines to each "forge'" vine

planting represented 64%. Planting on narrow rows would effectively double the per ha cost (to about NZS21,570/ha). Equivalent costs for the U trellis were NZ$11,435/ha, the GDC was NZ$10,638/ha and the TK2T was NZ$11,143/ha. Costs of the RT2T trellis with 3.6 m x 2 m spacing was $10,625/ha. These figures demonstrate that close row spac-ing is more expensive than divided canopies in terms of vineyard establishment. The economic advantage of improved training system design over the standard was clearly demonstrated by Crawford, being due primarily to increased yield. For example, Cabernet Franc vines trained to the standard trellis had an accumulated cash flow after 10 years of NZ$58,700/ha while for the RT2T the figure was NZ$114,500/ha.

Conclusion Canopy shade is a common problem in New World vine-

yards which can cause reductions in vineyard yield and winegrape quality. Practical techniques are presented as to how problem canopies may be identified and subsequently how they may be remedied. I propose that more attention be paid to "quality assurance" in the vineyard - using the described techniques to identify problems then appropri-ate management strategies to overcome them. Of the management strategies discussed, the use of large vine spac-ing with concomitant large node numbers and extensive canopy surface area offers opportunity to devigourate shoots and to induce water stress, important in _areas of

114 Proceedings Second International Cool Climate Viticulture and Oenology Symposium. Auckland. New Zealand

Canopy management: identifying problems and solutions

high rainfall, high soil water storage and low evaporation. The current fad of using close row spacing is likely to achieve only limited devigouration (see for example Remoue and Lemaitre 1985), but substantially increased costs of vineyard establishment.

Acknowledgements The authors would like to acknowledge the assistance of

Gary Woodbury and staff at Rukuhia Research Station, and Isabelle Gravett and Phil Allison for biometrical anal-ysis. Geoff Kelly chaired the tasting panels. Tom van Dam and Brent Fisher made the experimental wines.

Literature cited Baldini, E. Italian experience of double curtain training systems with special reference to mechanisation. In: Webb, A.D., Ed. Grape and wine centen-nial symposium proceedings; 18-21 June 1980; Davis, CA: University of California. Davis, CA: 195-200 (1982).

Bravdo, B., Hepner, Y., Loinger, C., Cohen, S. and Tabacman. H. Effect of crop level on growth, yield and wine quality of a high yielding Carig-nane vineyard. Am. J. Enol. Vitic. 35: 247-52 (1984).

Carbonneau. A., Casteran, P. and Le Clair, P.L. Essai de determination en biologic de la plant entire, de relations essentielles entre le bioclimat naturel, Ia physiologic de la vigne et la composition du raisin. Ann. Amelior. Plant 28: 195-221 (1978).

Carbonneau, A. Stress moderes sur feuillage induits par le systeme de conduite et regulation photosynthetique de la vigne. In: Bouard, J. and Pouget, R., Eds. Physiologic de la Vigne. Proceedings third symposium international sur la physiologic de la vigne; 24-27 June 1986; Bordeaux. France; Office International de la Vigne et du Vin, Pans, France: 378-85 (1987).

Clingeleffer, P.R. and Possingham, J.V. The role of minimal pruning of cordon trained vines (MPCT) in canopy management and its adoption in Australian viticulture. Aust. Grapegrower and Winemaker 280: 7-1i (1987).

Crawford, D.W. Economics of winegrape production on different trellis systems: a budgetary model approach. NI. Hort. Sci. thesis, Massey Univer-sity (1987).

Khmer, M.W. Vineyard canopy management—a review. In: Webb, A.D., Ed. Grape and wine centennial symposium proceedings; 18-21 June 1980; Davis, CA: University of California, Davis, CA: 342-52 (1982).

May, P. Trellising in relation to vine performance. In: Proceedings Second Wine Industry Technical Conference; 7-9 August 1973; Tanunda. South Australia. Australian Wine Research Institute, Glen Osmond, South Aus-tralia (1973).

Remoue, M. and Lemaitre, C. Comparison de different densities de plan-tation et methodes de culture du sol (non culture et enherbement perma-nent). Conn. Vigne Vin 19: 197-206 (1985).

Rotem, J. and Palti, J. Irrigation and plant diseases. Ann. Rev. Phytopath. 7: 267-88 (1969).

Shaulis, N.J., Amberg, H. and Crowe, D. Response of Concord grapes to light, exposure to Geneva double curtain training. Proc. Am. Soc. Hon. Sci. 89: 268-80 (1966).

Shaulis, N. and Smart, R. Grapevine canopies: management, microcli-mate and yield responses. In: Proceedings XIXth Int. Hort. Congress; 11.18 September 1974; Warsaw: vol. III: 254-65 (1974).

Smart, R.E.. Shaulis. N.J. and Lemon, E.R. The effect of Concord vine- yard microclimate on yield I. The effects of pruning, training and shoot positioning on radiation microclimate. Am. J. Enol. Vitic. 33: 99-108 (1982).

Smart, R.E. Vine manipulation to improve wine grape quality. In: Webb, A.D., Ed. Grape and wine centennial symposium proceedings; 18-21 June 1980; Davis, CA: University of California, Davis, CA: 362-75 (1982).

Smart. R.E. and Coombe, B.G. Water relations of grapevines. In: Kozlowski, T., Ed. Water deficits and plant growth. Academic Press, Lon-don: 137-96 (1983).

Smart, R.E. Canopy microclimates and effects on wine quality. In: Lee. T.H. and Somers, T.C., Eds. Advances in viticulture and oenology for economic gain. Proceedings of the fifth Australian wine industry techni-cal conference; 29 November-I December 1983; Perth, WA: The Australian Wine Research Institute, Urrbrae, SA: 113-32 (1984).

Smart, R.E. Principles of grapevine canopy microclimate manipulation with implications for yield and quality: a review. Am. J. Enol. Vitic. 36: 230-39 (1985a).

Smart, R.E. Some aspects of climate, canopy microclimate, vine physiol-ogy and wine quality. In: Heatherbell, D.A., Lombard, P.B., Bodyfelt, F.\'. and Price, S.F., Eds. Proceedings of the international symposium on cool climate viticulture and enology; 25-28 June 1984; Eugene OR: Oregon State University Technical Publication 7628, Corvallis, OR. 1-19 (1985b).

Smart, R.E., Robinson, J.B., Due, G.R. and Brien. C.J. Canopy microcli-mate modification for the cultivar Shiraz I. Definition of canopy microcli-mate. Vitis 24: 17-31 (1985).

Smart, R.E. Canopy management to improve yield, fruit compositiion and vineyard mechanisation: a review. In: Lee, T.H., Ed. Proceedings of the sixth Australian wine industry technical conference, 14-17 July 1986; Adelaide, SA: The Australian Wine Reseach Institute, Adelaide, SA: 205-11 (1987a).

Smart, R.E. The light quality environment of vineyards. In: Bouard. J. and Pouget, R., Eds. Physiologic de la Vigne. Proceedings third sympo-sium international sur la physiologic de la vigne; 24-27 June 1986; Bor-deaux, France; Office International de la Vigne et du Vin, Paris, France: 378-85 (1987b).

Smart, R.E. Influence of light on composition and quality of grapes. Acta Honiculturae 206: 37-47 (1987).

Smart, R.E., Dry, P.R. and Loftier, L. Critical relations of shoot spac-ings in vineyards. In: Bouard, J. and Pouget, R., Eds. Physiologic de la Vigne. Proceedings third symposium international sur la physiologic de la vigne; 24-27 June 1986; Bordeaux, France; Office International de Ia Vigne et du Vin, Paris, France: 378-85 (1987).

Soderlund, R., Orr, K., Gallagher, K., Porlet, D., and Harding, E. Responses of Cabernet Sauvignon grapevines to lighter pruning. Aust. Grapegrower and Winemaker 280: 40-5 (1987).

Van den Ende, B. The Tatura trellis—a system of growing grapevines for early and high production. Am. J. Enol. Vitic. 35: 82-7 (1984).

Shaulis, N.J. Responses of grapevines and grapes to spacing of and within canopies. In: Webb, A.D., Ed. Grape and wine centennial symposium proceedings; 18-21 June 1980; Davis, CA: University of California, Davis, CA: 353-61 (1982).

Proceeaings Secona international Cool Climate Viticulture ana Oenology Symposium. Auckland. New Zealand. January 1988.

72

JULY/AUGUST 2002 121

Yield limits for vineyards -

mandated inefficiency? Did you hear the story about the grapegrower who walked into a winery at crush and demanded that the enologist extract only 100 gallons of wine from each ton of his grapes? To extract any more, he said, would be to; compromise the wine quality

I don't hear that story tali* but I have heard the follow-ing one many times: AA. etiologist (or winery field rep) walked into the vineyard kid asked that yield be lowered to three tons per acre, when a gbt -ton per acre crop was hanging. The higher yield, he said, would compromise wine quality.

Grape surplus — need for higher quality? or less fruit?

There are stories of large grape surpluses for the 2002 harvest in California. This is particularly acute in the Central Valley for Cabernet Sauvignon, but each region will likely have problems. During my stay. at Cal Poly State University (San Luis Obispo), I heard stories of problems (potential surpluses) with Cabernet Sauvignon on the Central Coast. The same was true for Australia,fpr the 2002 harvest, but an over-all low volume vintage reduced the pressure towards the end.

Not unexpectedly, at times of potential surplus, the pres-sure is on growers to limit yields. I am eversure if the yield

an limits are meant to .possibly improv quality or merely to

reduce the wineries' to tak fruit for which they may have no wine. market, " boo,

In this column I want to review tkie situation, regarding vineyard yield and wine quality.

Vineyard yield and wine lity The notion that low yield3g vineyards make better wine is

quite widespread through4the world. I think it is European in origin, and probably Fiench. The idep dates back to Roman times: "a struggling vine makes the best wine." Yield limits are defined under AOC appellation systems in France.

Many have questioned, however, whether quality can be imposed by legislation. The important issue to examine is whether low yields guarantee high quality. Does removal of some fruit guarantee the remainder will have improved quality? In the remarks that follow, I will principally concern myself with red wines, though I believe that the same principles generally apply to white'wines. . .

It is my observation that many of the world's great red wines are grown with some stress. This is typically a water stress — enough to stop shoot growth before veraison and to limit lateral leaf growth. I believe that, if the stress is mild, then there is only a small effect on yield.

However, a considerable amount of stress can greatly reduce yield, with 'a corresponding reduction in quality. I have seen severely4noisture-stressed vines struggling to ripen fruit. Some leaves have fallen off, and the remainder are yellow. It is obvi-

ous that the leaves are hot and stomates are closed, so the remaining leaves are not working efficiently. It is indeed naïve to assume that maximum stress gives maximum quality.

Is it the lower yield or the mild stress which promotes quality? Or maybe a combination of both? I think we must be very careful to separate these effects. It is my opinion that the stress that causes lower yield is more likely to lead to higher quality than is the lower yield itself

Let me clarify with an example: Imagine a vigorous Cabernet vineyard grown on deep soil and carrying an eight-ton

. ton per acre crop. Will quality be improved by thinning to four tons per acre? I doubt it. More likely the vines will be put even more out of balance, and the fruit probably even more shaded.

In this instance, I think the grower should be more con-cerned about affecting a modicum of stress at the right time, rather than merely dropping fruit. In other words, the excess of shoot tips growing at veraison are more likely to damage quality than are a purported excess of grapes.

Small berries, are they important? I also think the contribution of small berries to wine quality is

over emphasized. Certainly, a small berry has a larger surface-area-to-volume ratio, and so more skin to juice. But across the range of commercial berry sizes these changes are relatively small.

Researchers in Australia have made wine from large and small berries within loads and found no difference in compo-sition and quality. I think that it is the factors making berries small that lead to quality, and not the small berries themselves. Small berries are a sign of stress.

Water stress — especially before veraison — will cause smaller berries. Crop thinning at this time will cause larger, not smaller berries. The easiest way to have small berries is by minimal pruning, but I believe that few enologists will endorse this practice!

Some experimental results I have investigated the relationship between yield and

quality in several experiments, in both hot and cold climates. One of my first trials was with Syrah at Angle Vale in South Australia, a hot region like California's Central Valley. I com-pared a high yielding Geneva Double Curtain (GDC) to an open canopy with a "sprawl canopy" that was shaded.

The results were clear, and dramatic. The higher yielding GDC at 11 tons per acre produced wine with better color and phenols than did the sprawl at nine tons per acre. The respec-tive sensory scores in a replicated tasting using wine industry judges was 15.4 ex 20 and 11.9 ex 20.

4 have found similar trends in cool climates. As an example, a trial with 'Cabernet Franc in New Zealand showed that a high. yielding, open canopy carrying 12 tons per acre made better wine than a shaded vertical shoot positioned (VSP) trellis with six tons per acre. There was lower pH, more color, anthocyanins, and phenols for the higher yielding vines, and the sensory scores were 5.1 ex 7 for high yield and 3.5 ex 7 for low yield.

I have seen other results with similar outcomes. For exam-ple, many fruit thinning trials show little or no benefit on fruit composition.

323

Balanced vines are important I believe that balanced vines make balanced wine. A balanced

vine will have appropriate leaf area to ripen grapes, but not so much as to cause shading. Vme balance is achieved by using the correct trellis system and pruning level for the site, and maybe some other practices, such as irrigation management arid cover cropping, to produce a modicum of water stress.

Are there exceptions? In my experience there are some varieties that indeed

seem yield-sensitive in relation to quality. The best example is Pinot Noir. I am unaware of any premium quality Pinot Noir being made from a moderate to high-yielding vineyard. It seems that this variety requires a larger than normal leaf-to-fruit ratio to produce quality wine. Pinot Noir seems as fussy about its yield as it is about where it is grown.

There are a few other examples, typically with large berry and large clustered varieties like Zinfandel, Merlot, and Tempranillo. These varieties can set crops larger than they have leaf areas to ripen, so composition is improved by crop thinning.

The future I doubt that many winemakers will take seriously what I say

above. Perceptions about yield and wine quality are deeply ingrained, and often repeated by wine writers. So growers can

look forward to being requested to limit their efficiency (and income) by dropping crop while the market is tight.

I do believe, however, that in 10 years things may be different. There will be more use of winery-based measures of grape composition and quality, as, for example, in grape color. New instruments using near infrared spectral analysis show great prOmise for real-time quality assessment during grape receiving at the winery. I also suspect that there will be more field trials looking at the relationship of yield to quality, especially looking at crop thinning.

For the moment, I can offer winemakers a tip. Within any one region of similar climate, and for any given variety, the first vineyards to ripen often make the best wine. Harvest date can be a better indicator of quality than can yield. I think that more attention should be paid to irrigation practice and canopy management and vine balance, and less to yield. That will be to everyone's ultimate benefit. ■

Dr Richard Smart, "the flying vine-doctor," is an international viticultural consultant based in Australia. He ii also the Visiting Professor of Viticulture at Cal Poly; San Luis Obispo, CA. He can be contacted by e-mail at: vinedoctor@compuserve.com . Read about Dr. Smart's business including his consulting schedule, educational wine tours, and seminars at his home page http://www.smartvit.com.au