Practical Aspects of Crop Load and Canopy Management Jim Wolpert Extension Viticulturist Department of Viticulture and Enology University of California, Davis Penn State Grape Day August 10, 2011
Presentation Outline Why worry about your crop load Consequences of overcropping Components of yield Variability in yield Estimation of yield Crop load management Pruning vs Thinning Canopy management Research with thinning (if time permits)
Why worry about crop load Contracts are usually written by the acre but buyers think in terms of tons Consequences of too much crop Winery: Fermentor sizes, marketing issues Grower: Last minute scramble for a buyer Consequences of too little crop Winery: Last minute scramble for other sellers Grower: Unnecessary thinning leads to lost crop
Overcropped vines Somewhat overcropped vines Sugar accumulation is delayed, upsets Brix/TA balance Target harvest Brix may not be met Poor color in reds Severely overcropped vines All the above Poor cane maturation (green shoots do not turn brown, green portion dies with the first freezing temps) Reduced bud fruitfulness the following year (i.e. fewer clusters per shoot) Slow or inhibited budbreak the following year
Napa Valley Crop Statistics source: Napa Valley Agricultural Commissioner's Crop Report Cab franc Cab Sauvig Malbec Merlot Zinfandel Total Blacks Tons / Acre 6 4 2 0 Tons / Acre 6 5 4 3 1970 1980 1990 2000
Yield (kg Vine -1 ) 10 8 6 4 0 352 75 121 78 96 4 76 118 124 132 130 131 WEN Chardonnay Clones Sonoma County 352 4 75 96 118 121 124 132 130 131 76 78 WEN 4 132 96 118 121 130 352 124 131 75 76 78 WEN 1998 1999 2000 2001 Year 4 118 121 96 124 130 131 132 352 75 76 78 WEN
Other reasons to thin Quality over-cropped Too much fruit to produce the desired wine quality - Obtain the desired Brix but not concentration To increase crop uniformity The fruit is not ripening evenly and the less mature fruit needs to be removed In practice, growers wait until 80% clusters have colored at veraison and drop the 20% still green, referred to as green drop
Components of Yield Vines per acre Buds per vine Shoots per bud Clusters per shoot Berries per cluster Weight per berry
Components of Yield Vines per acre Original stand not 100% Tractor blight Gophers Pierce s Disease Replants that didn t catch up
Components of Yield Buds per vine Variability from pruner to pruner Compensation for weak areas in the vineyard Compensation for weak vines Compensation for weak shoots ( 1-bud )
Components of Yield Shoots per bud Generally pretty constant Too many buds retained for a vine s capacity = reduced % budbreak Frost Wind breakage Shoot thinning pass
Components of Yield Clusters per shoot Variety dependent Dependent on temperature during cluster initiation the previous season Especially, the size of the second cluster can greatly affect yield
Components of Yield Berries per cluster Size of the cluster established during initiation the previous year Fruitset dependent on weather during flowering Cool, wet conditions can dramatically reduce fruitset
Malbec Clones Oakville
Components of Yield Weight per berry Influenced by seed number Weather conditions during Phase 1 of growth Irrigation regime Desiccation at the end of the season
Vine Internal Compensations in Yield Very high bud number per vine, increases number of blind buds, i.e. % budburst decreases When cluster number per vine increases, fruitset per cluster decreases When number of berries per vine increases, berry size decreases
Variability in Yield Variability can be found among: Vines in a vineyard Shoots on a vine Clusters on a shoot Berries on a cluster
Crop Estimation Approaches Visual estimate, eye-ball it Cluster count (spring) x ave cluster wt Same vines every year Or random vines every year Tends to under-estimate the big crop years and over-estimate the small crop years, because cluster wt varies Need to account for the size of the 2 nd cluster as a fraction (0.2, 0.4 etc)
Statistical Approach Randomly select 10 vines Record vine measurements individually Calculate the standard error Use a statistical table to determine how many more vines must be sampled As vine-to-vine variability goes up the number of vines needed goes up Wolpert, J. A. and E. P. Vilas 1992. Estimating vineyard yields: Introduction to a simple, two-step method. American Journal of Enology and Viticulture 43:384-388
Uniform Shoot Growth
Non-uniform Shoot Growth
Non-uniform Shoot Growth
Fruit thinning by shoot length No clusters 1 cluster 2 clusters
Other reasons to remove fruit Clusters are bunched together Physiological issues Sunburn, rachis collapse Pest and disease issues Rot, mildew etc The winery asks you
Shoots crossing, clusters congested
Goal in Crop Management To strike a balance between vegetative growth and reproductive growth Leaves are the source of carbohydrates (sugars and starch) Fruit are the sinks for carbohydrates Remember there are other sinks too: cordons, trunks and roots
Measures of Balance Yield:prunings ratio ( Ravaz Index RI) RI an estimate of leaf area/crop wt But leaf area is difficult to measure Shoot density (12-15/meter, 4-5/ft long) Too crowded leads to shading Pruning weight (kg/m, lbs/ft) Shoot weight (g/shoot)
Measures of Balance Yield:prunings ratio (Ravaz Index) Yield per vine / pruning wt per vine On unthinned vines Low tech Ratio of 5 10 for most varieties Individual varieties have a narrow range Not absolute Cabernet < 5 is OK Chardonnay > 10, maybe OK
Pruning vs. Thinning Pruning sets crop yield potential More buds = more clusters = more yield But More buds = more shoots, growing points And More shoots = less growth per shoot Less growth = less leaves per cluster
Conclusions about crop load Crop estimation is inherently difficult Climate effects Vineyard variability Crop load management requires judgment calls
Canopy Management Shoot thinning Leaf removal Shoot positioning Summer pruning - hedging
Shoot thinning Removal of latent (non-spur) shoots Opens up the canopy Facilitates pruning the following winter Done in springtime, by hand Timing is critical Too early: will miss late developing shoots Too late: shoots will be lignified (woody) and difficult to remove
Shoot Thinning Reduces shoot density, but impact on canopy density is often temporary Efficient method of crop thinning Assists in the establishment of spur positions Reduces pruning costs Cost per acre - $125 $300/acre
Leaf Removal
Leaf Removal Consists of the removal of basal leaves and lateral shoots in the fruit zone
Leaf Removal Microclimate Increases sunlight and temperature in fruit zone Decreases humidity in fruit zone
Leaf Removal Sunburn Risk is minimized if fruit is exposed immediately after berry set and on east or north side only Risk is maximized if fruit developed in canopy shade is exposed prior to berry softening
Leaf Removal Cost $125 - $250/acre depending upon : Severity Timing Canopy density
Shoot Positioning
Summer Pruning or Hedging
Summer Pruning / Hedging Top & Trim canopy sides (Positioned canopies) Cut canes off vineyard floor
Summer Pruning / Hedging Increases light penetration, temperature in fruit zone Decreases humidity in fruit zone Maintain shape for positioned canopies
Summer Pruning / Hedging No effect on fruit composition if minimal amounts of foliage are removed May delay fruit maturity if large amounts of foliage are removed
Fruit thinning research
We want uniformity; that green fruit will never catch up so we need to remove it
The Vineyard Napa Valley Stag s Leap District Cabernet Sauvignon clone 5 101-14 Mgt rootstock Control vines Tons per Acre 4.9 Yield : Pruning Weight 3.8
The Treatments Treatment Timing Cluster Thinning Treatment Clusters P-20 Pea Stage 20% random P-40 Pea Stage 40% random V-20 80% Veraison 20% random V-40 80% Veraison 40% random VG-20 80% Veraison 20% greenest 21B-20 21 Brix 20% random 21B-40 21 Brix 40% random UT-80R 80% Veraison retained reddest 80% UT-20G 80% Veraison retained and tagged greenest 20% UT-GG 80% Veraison retained and tagged would have been green dropped Control unthinned
Wappo Hill, Napa County Cabernet Sauvignon 2005 Thinning Trial 26 8/1 8/15 8/29 9/12 9/26 10/10 10/24 P-20 P-40 V-20 V-40 21B-20 21B-40 VG-20 UT-80R UT-20G UT-GG C Brix 24 22 20 18 0 8/24 9/6 9/20 9/28 10/13 19.5 22.0 24.0 25.0 26.0 19.0 21.5 23.5 24.5 25.5 Brix 18.5 21.0 23.0 24.0 25.0 18.0 20.5 22.5 23.5 24.5 17.5 20.0 22.0 23.0 24.0
Regardless of when fruit was removed or how much was removed, there were no significant differences in Brix at harvest (~25 Brix)
Maybe the berries that were behind at veraison are still behind at harvest, i.e. the clusters that were green are less uniform raisins + green fruit (ave of 30+22) Brix = 26 each berry 26 Brix Brix = 26
20 Brix 21 Brix 22 Brix 27 Brix
0 20 21 22 23 24 25 26 27 28 40 30 UT-20G UT-80R UT-GG C Density Population % 20 10 0 40 30 13 oct 2005 Control V40 20 10 0 28 sept 2005 0 20 21 22 23 24 25 26 27 28 Brix
Population (%) 50 40 30 20 10 Control Green Drop 11 Sept 2003 23 Sept 2003 0 0 18 20 22 24 26 Soluble Solids (Brix) 0 18 20 22 24 26 28 Soluble Solids (Brix)