Crop Load ManagementScience or Belief System?

Andrew G. ReynoldsCool Climate Oenology & Viticulture

InstituteBrock University, St. Catharines, ON

Low yield = High wine quality?

The Belief System

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Crop Load ManagementMust be About Balance

The Balance “Sweet Spot”

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SHADESHADEOVERCROPPING

BALANCE

HIGH VIGOUR SITE

LOW VIGOUR SITE

What is Balance?

• Mean individual cane weights of 25 to 40 g

• Cane pruning weights of 0.3 lbs./ft of canopy (0.4 kg/m canopy)

• Crop loads (Ravaz Index; crop size to vine size ratio) > 5 < 12– Closer to the low end for Pinot noir and late-

maturing reds and nearer to the high end for aromatic whites

Ravaz Index ca. 10Crop Size Vine Size

Red

uce

crop

size

Berry Maturity

Low GDDPoor seasons

RainWinter injury

risk & spacing

Increase vine size

Balanced vines = High Wine Quality

Vines at Chateau Margaux in clay. Balanced at 2 t/a

Balanced vines = High Wine Quality

Vines at Chateau Couhins in gravel. Balanced at 6 t/a

Points to Remember About Crop Management

• Crop control can be achieved by both pruning and cluster thinning

• Taking aim at a reasonable shoot density (e.g. 15 shoots/m row) should minimize shade and get you close to the target crop load

• I suspect that most so-called crop load effects are often shoot density/ shade effects

• Often severe pruning can lead to low crops + high shading and can be just as detrimental as overcropping (q.v. Chapman et al.)

Shoot Density

15-25 shoots/m row

• High fruitfulness• Optimum bud hardiness• High Brix; low TA and pH• Enhanced varietal

character• Minimized vegetal aromas• Enhanced color

High (or very low) shoot density

• Low fruitfulness• Low Brix; high TA/pH• Reduced varietal

character, e.g. monoterpenes

• Increased vegetal flavors• Poor color

Points to Remember About Crop Load Management

• Responses to crop load reduction will vary substantially – From site to site– Between varieties– Across vintages– Depending on when crop adjustment is done

• Making general conclusions may be difficult and recommendations need to be tailored to each situation (here goes 45 minutes of ambiguity…)

Crop Load Management1. Some Varieties are Non-Responsive

(…and others are very responsive)

Pinot noir: Response to Shoot Density and Crop Level

Pinot noir: Response of yield and fruit composition to shoot density, Okanagan Falls, BC 1989.

These are non-crop related shade responses. (A 20 shoot/m Scott Henry treatment improved fruit composition vs 10

shoots/m)

Shoot density

(s/m row)

Yield (t/ha)

Brix TA

(g/L)

pH Wine Anthocyanins

(mg/L)

10 9.7 23.4 6.2 3.35 209

20 14.6 22.3 6.7 3.28 180

Sig. F ** ** ** * **

Pinot noir: Response of yield and fruit composition to crop level, Okanagan Falls, BC 1991

The crop level response may not be as large as expected

Crop level Yield (t/ha)

Brix TA

(g/L)

pH Wine Anthocyanins

(mg/L)

Full 12.1 24.2 11.0 3.49 99

Half 8.8 24.9 11.2 3.51 107

Sig. F *** ** ns ns ns

Some sensory effects of crop level reduction on BC and OR Pinot noir, 1989-92

Proof is in the glass

Reductions• Vegetal aroma (BC)• Vegetal flavor (BC)• Grassy aroma (OR)

Increases• Color (BC & OR)• Spicy/black pepper aroma (BC)• Fruity flavor (BC & OR)• Berry aroma & flavor (OR)• Tree fruit aroma (OR)• Currant flavor (BC)• Astringency (BC & OR)• Finish (BC)

Riesling: Response to Shoot Density and Crop Level

Factor Leaf area on laterals

Yield (t/a)

Brix TA (g/L)

pH cis-3-hexanol (g/L)

Linalool (g/L)

Shoot density (shoots per m row)

16 159 10.9 21.4 12.8 3.00 62 25

26 70 14.4 20.7 13.0 2.94 67 22

36 76 16.5 20.9 13.0 2.97 78 21

Trend L** L***,Q** L,Q* NS L*,Q** L*** L*

Crop level (clusters per shoot)

1 88 12.4 21.4 12.8 3.01 66 25

1.5 96 14.3 20.8 13.0 2.96 57 22

2 119 15.4 20.8 12.9 2.94 81 21

Trend NS L*** L** NS L*** L,Q*** L**

Riesling: Impact of shoot density & crop level on growth, yield, and fruit composition, Kelowna, BC, 1989-90

Riesling—Impact of Crop Level on Aroma Compounds

A notable reduction in “green” compounds with crop thinning

Riesling—Impact of Crop Level on Sensory Attributes

Green fruit character is diminished by thinning

PCA of sensory data, Riesling shoot density X crop level, Kelowna, BC 1989

Shade ultimately plays perhaps a greater role

36 shoots/m

26 shoots/m

16 shoots/m

Clusters/shoot: Solid= 2; bold= 1.5;open= 1

Chardonnay Musqué

Yield vs BrixA clear yield: Brix relationship

THINNED TREATMENTS

Muscat Aroma vs. Overall Quality Brix has little apparent effect

NON-THINNED

Chardonnay Musqué SensoryThinning in some cases ineffective; Time of thinning not critical

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Floral (ns)

Lychee (ns)

Dry fruit (**)

Citrus (*)

Spicy (*)

Grassy (****)

FLORAL (ns)

LYCHEE (ns)

DRY FRUIT (ns)CITRUS (*)

SPICY(*)

GRASSY (ns)

ACIDITY (ns)

ASTRINGENCY (ns)

BODY (ns)

FINISH (ns)

COLOR (****)

Late bloom/early set Early stage I Late stage I

Lag phase Veraison Non-thinned (control)

Response of Icewines to Crop Load Manipulation

Sensory Map of the Significantly Different Attributes in 2003 Vidal Crop Level Icewines

Biplot (axes F1 and F2: 63.83 %)

CL1R1

CL1R2

CL2R1CL2R2

TSR1

TSR2

TVR1

TVR2Caramelized Aroma

Dried Fruit / Raisin Aroma

Peach Aroma

Pear / Apple Aroma

Pear / Apple

Sherry

Tangerine

Tropical Fruit

Bitter-8

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F1 (43.73 %)

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• All sensory attributes associated with the thinned treatments

• Thin at veraison associated with several aroma & flavour attributes

Data courtesy Amy Bowen, Brock University

Sensory Map of the Significantly Different Attributes in 2004 Vidal Crop Level Icewines

• Most attributes associated with the thinned treatments

• Except nut flavour which is loaded with the control

• Nut and honey are inversely correlated

Biplot (axes F1 and F2: 79.83 %)

CLR1

CLR2

TSR1TSR2

TVR1

TVR2

Citrus AromaFloral Aroma

Lychee Aroma

Banana

Honey

Nut

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F1 (56.54 %)

F2

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Crop Load Management2. Some Fruit Composition Variables are Non-

Responsive

Individual Phenols, Cabernet Sauvignon 2004

Catechin, quercetin non-responsive

babb

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Gallic acid Catechin Epicatechin

Caffeic acid p-Coumaric acid Quercetin

Individual Non-acylated Anthocyanins,

Cabernet Sauvignon 2004Most non-acylated pigments responded to crop reduction

aaab aaabb abbc abbc

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Delphinidin Cyanidin Petunidin Peonidin Malvidin

Individual Acetylated Anthocyanins, Cabernet Sauvignon 2004Some, e.g. malvidin, were not responsive

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Delphinidin Cyanidin Petunidin Peonidin Malvidin

Crop Load Management3. Season can be Critical

Brix, Cabernet Franc 2004-06Cluster thinning increases in only 2 of 6 cases; leaf removal alone no

effect or reduced

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Anthocyanins, Cabernet Franc 2004-06BLR ineffective; CT increased in 2 of 3 years; CT+BLR not additive

abab

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TREATMENT

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Colour Intensity, Cabernet Franc 2004-06

BLR again ineffective; thinning increased colour in 2 of 6 instances

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Total Phenols, Cabernet Sauvignon 2004-06

Cluster thinning increased phenols in 2 of 6 cases; BLR alone only once

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Sensory attributes, Cabernet Franc, as impacted by viticultural treatment, 2004

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70red fruit

black fruit (****)

black pepper

bean/pea (*)

mushroom

tobacco

RED FRUIT

BLACK FRUIT (***)

BLACK PEPPER (****)

BEAN/PEA

MUSHROOM

TOBACCO (*)

ASTRINGENCY (**)

BITTERNESS

VISCOSITY (*)

LENGTH (***)

CONTROL CT BLR + CT

Sensory attributes, Cabernet Franc, as impacted by viticultural treatment, 2005

A- Cabernet Franc Viticulture 2005

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red fruit

black cherry

black currant (*)

black pepper

green vegetable

canned vegetable (*)

chocolate (*)

spicy

earthy

RED FRUIT

BLACK CHERRY

BLACK CURRANT

BLACK PEPPER

GREEN VEGETABLE

COOKED VEGETABLE (*)

CHOCOLATE (*)

SPICY

EARTHY

ACIDITY (**)

ASTRINGENCY (***)

VISCOSITY (*)

LENGTH (*)

CONTROL CT BLR + CT

Crop Load Management4. Timing is Sometimes Crucial to Quality (but often not!)

Chardonnay Musqué FVTThinning was beneficial; early timing most effective

Chardonnay Musqué PVTThinning was beneficial; timing apparently not critical

Chardonnay Musqué Sensory PCAThinning was of questionable benefit; timing apparently not critical

Cluster thinning -- When to do itTiming Advantages Disadvantages

Flower cluster

1. Rapid and relatively inexpensive

2. Yields are not reduced

3. Vine size is maintained or increased

4. Fruit composition is improved

1. Can lead to large berry size and reduced skin:juice ratios

2. Can increase 2nd crop and lateral shoot formation

3. Improved berry set can increase bunch rot

Stage I 1. Only slight yield reductions

2. Vine size and fruit composition are still improved

3. Reduces berry set slightly and clusters are thus less bunch rot-susceptible

1. More expensive

2. Less effective– the canopy is fully-formed and clusters are harder to find

Cluster thinning -- When to do itTiming Advantages Disadvantages

Pre-veraison

1. Yields are reduced and skin:juice ratio is increased

2. Fruit composition is improved

Expensive—labor + loss of crop

Post-veraison to harvest

1. As with pre-veraison, but results are more extreme

2. Could thin off a brandy and a bubbly crop first

As with pre-veraison

No thinning

1. Saves money

2. Higher yields

3. The right thing to do in some years, sites, varieties

1. Possible long term reductions in yield and vine size (maybe)

2. Compromised fruit composition (maybe)

When to Thin

• To reduce a potential overcrop situation in a specific year that may have resulted from conditions the previous year

• To maintain consistent yields and fruit composition in varieties with fruitful base shoots and/or secondary/ tertiary buds (mainly hybrids)

• To avoid overcropping in large-clustered varieties, particularly Syrah, Grenache, Mourvedre, Zinfandel, Bordeaux reds, etc.

• To get a crop to mature in a difficult year

Conclusions and Final Thoughts

• Responses to crop load reduction will vary substantially – From site to site– Between varieties– Across vintages– Depending on when crop adjustment is done

• Making general conclusions may be difficult and recommendations need to be tailored to each situation

• Often so-called crop level effects may actually be due to shade– either excess shoot density or excess shoot vigor due to overly-severe pruning

Crop Load Management:Science, Belief System, or 45

Minutes of Ambiguity?