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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
0
20
40
60
80
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120
0 2 4 6 8
YIELD (t/acre)
WIN
E Q
UA
LIT
Y .
Crop Load ManagementMust be About Balance
The Balance “Sweet Spot”
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YIELD (t/acre)
WIN
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UA
LIT
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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
0
10
20
30
40
50
60
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
-6
-4
-2
0
2
4
6
8
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12
F1 (43.73 %)
F2
(20.
10 %
)
• 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
-4
-2
0
2
4
6
8
10
-10 -8 -6 -4 -2 0 2 4 6 8 10
F1 (56.54 %)
F2
(23.
29 %
)
Crop Load Management2. Some Fruit Composition Variables are Non-
Responsive
Individual Phenols, Cabernet Sauvignon 2004
Catechin, quercetin non-responsive
babb
bab
aa
b
abb
caab
abcc abab0
10
20
30
40
50
Control BLR CT CT+BLR
TREATMENT
Co
nce
ntr
atio
n (
mg
/L)
.
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
aabbc
0
20
40
60
80
100
120
140
160
Control BLR CT CT+BLR
TREATMENT
Co
nce
ntr
atio
n (
mg
/L)
.
Delphinidin Cyanidin Petunidin Peonidin Malvidin
Individual Acetylated Anthocyanins, Cabernet Sauvignon 2004Some, e.g. malvidin, were not responsive
aaabaabab aaab
aabbc
ababab
0
10
20
30
40
50
60
Control BLR CT CT+BLR
TREATMENT
Co
nce
ntr
atio
n (
mg
/L)
.
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
b
a
cb
AB
A
BAB
ZYY
Y
19
20
21
22
23
24
25
26
Control BLR CT CT+BLR
TREATMENT
Bri
x
2004 2005 2006
Anthocyanins, Cabernet Franc 2004-06BLR ineffective; CT increased in 2 of 3 years; CT+BLR not additive
abab
bB
AB
B
0100200300400500600700800900
Control BLR CT CT+BLR
TREATMENT
To
tal an
tho
cyan
ins
(mg
/L)
.
2004 2005 2006
Colour Intensity, Cabernet Franc 2004-06
BLR again ineffective; thinning increased colour in 2 of 6 instances
B
AB
A
ZZYY
0
5
10
15
20
25
Control BLR CT CT+BLR
TREATMENT
Co
lor
inte
nsi
ty (
AU
) .
2004 2005 2006
Total Phenols, Cabernet Sauvignon 2004-06
Cluster thinning increased phenols in 2 of 6 cases; BLR alone only once
aaabAA
BA
0
500
1000
1500
2000
2500
3000
3500
Control BLR CT CT+BLR
TREATMENT
To
tal p
hen
ols
(m
g/L
)
2004 2005 2006
Sensory attributes, Cabernet Franc, as impacted by viticultural treatment, 2004
-10
10
30
50
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
0
10
20
30
40
50
60
70
80
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?