Following our best practice session, I thought it would be prudent to have this document on hand and bring attention to this topic. It is useful to discuss and clarify any misconceptions regarding this important practice.
As you read, you may recognize that you may not go into as much detail, but it is useful to understand each component of yield estimation, how we derive these numbers and why it is important to do the count each year.
Remember, each vintage is
different, and yield differs annually. It is not useful to base your current
yield on previous yield numbers. What the historical average does do is provide
a benchmark for a particular variety at your specific site.
If you have
any questions, please don’t hesitate to contact me.
So, What
is Yield?
Typically,
the weight of fruit over a given area (tonnes/acre of grapes). In some cases,
yield may refer to the amount of fruit on an individual vine.
Why is
yield estimation important?
Yield estimates at or near veraison help growers to make important decisions that can
affect the end quality and quantity of the grape harvest.
Purpose
of Yield Estimation
The practice helps vineyard managers to:
- Pre-determine harvest yields in anticipation for processing.
- Make fruit thinning decisions and crop load adjustments, manage vine health and balance their vines as early as possible.
- Improve harvest scheduling.
- Allocate winery space.
· In the winery, early estimates assist with purchase of goods and supplies necessary to process the crop. Scheduling and coordinating processing and tank space is critical in keeping the work-flow of a winery under control.
Yeast, fining agents, barrels, and tanks all need to
be ordered and ready by the time harvest begins.
The amount of fruit in a vineyard,
which is the most common form of yield presentation (tonnes per acre) is often
dictated by contract specifications.
·
Taking both business and viticultural factors into consideration, the
appropriate crop load for the same site can vary from year to year.
· The long-term mismanagement of crop load can have negative consequences.
Over-cropping vines can lead to:
- A vine’s depleted carbohydrate reserves for survival (which are necessary for overwintering and spring growth).
- Reduced potential bud fruitfulness by stressing the vine during fruit bud initiation (beginning post bloom through to veraison) . If vines are repetitively over-cropped year after year, it can make the vine susceptible to becoming unfruitful and may lead to shortened life span.
Under-cropping the vine can lead to:
- Management challenges of unregulated or overly vigorous vegetative growth. Under cropping requires too much vine growth adjustment ( excess need for hedging, shoot thinning and topping, etc.)
- Wasting photosynthetic energy which is used for vegetative growth instead of reproductive growth. The result of under cropping can lead to an excessively large canopy, excess shading, oversized leaves and increased disease susceptibility (mildews , rots, and other pest pressures ) and making pesticide coverage very difficult . Such canopies can lead to less mature and unbalanced fruit potential.
Crop Estimation Timing and Method:
Crop estimation can be performed several times during the year, but ideally should take place around veraison.
The traditional method uses current season cluster
counts and the average cluster weight from the previous season or from averages
determined from multiple years of weighing clusters at harvest. However, yield will
vary from year to year, and it is important that yield estimation be conducted
for each block/cultivar for each vintage.
Yield Estimation Factors:
- Planting density (# of vines/ acre)
- Number of producing vines/acre
- Average number of clusters/vine
- Average cluster weight
1. Number of Producing Vines per Acre
This is determined by row and vine spacing. The number of missing/ damaged/ new vines/ under-producing vines must also be taken into consideration. Therefore, the number of actual vines may be lower.
2. Number of Clusters per Vine
This number
varies with the level of canopy management. For example: increasing the
severity of pruning, shoot thinning or cluster thinning may decrease the total number
of clusters per vine. Number of clusters can be counted as late as
pre-veraison. The more vines you sample, the more accurate your numbers will
be. Remember, all clusters on the selected vines must be counted. Select the
vines in an even way; for example: every 25th vine in even rows
(Dami and Sabbatini 2011). Do not select damaged or under-producing vines when
counting. You are looking for a representation of “average” vines to represent
the whole block.
Alternatively,
you may also count the number of clusters per 1 meter of row length at multiple
locations throughout the block for each cultivar
3. Cluster Weights
Cluster
weights also vary with each vintage. Wet weather during bloom, dry summers and disease
infections (black rot, powdery mildew and downy mildew) all may cause poor
fruit set and have negative effects on berry weight.
Average
cluster weights must be obtained from the same vines where cluster numbers
were counted.
Obtaining
cluster weights at harvest is not used to predict yield in the current
season, but to provide a data base for estimations in subsequent years.
Harvest Cluster Weight Method.
This method
depends on consistent cluster weights from one season to the next. Components
of yield vary each year depending on the weather, site, variety and cultural
practices:
PY (predicted yield) = (ANV x NC x CW) / 1000
Where PY = predicted yield (tonnes per acre)
ANV = actual number of vines per acre
NC = number of clusters per vine
CW = cluster weight (in kg) ( for
example 125 grams = 0.125 kg)
If ANV = 1050, NC =25 and CW (avg for primary and secondary clusters is 125 grams
Then PY = (1050 x 25 x
0.125)1000
= 3.28 tonnes per acre
Whether you do the estimation early in the season, or pre-veraison, it is important to remember that every year is different and the predictions will not be the same as the previous year.
I hope this is helpful in shedding some light to this crucial annual practice.
As you are probably aware, harvest is slowly underway, so again, if you have any questions, please don't hesitate to contact me. I will be on the road for most of next week- Malagash and South Shore, so if you would like a quick visit, do let me know.
Thank you for your time.
Cheers!
Katarina
Katarina Vucic MSc DipWSET
Viticulture Specialist
Perennia Food and Agriculture
Email kvucic@perennia.ca
Office 902-678-7722
Cell 902-599-1390
References:
Barriguinha,
André et al. Vineyard Yield Estimation, Prediction, and Forecasting: A
Systematic Literature Review. https://www.researchgate.net/publication/354418517_Vineyard_Yield_Estimation_Prediction_and_Forecasting_A_Systematic_Literature_Review
Sabattini,
Paulo. Introduction: Crop Estimation and Vine Growth. Predicting Harvest Yield in Juice and Wine Grape
Vineyards - MSU Extension
Komm, Brittany et al. Vineyard Yield Estimation. Washington
State Extension. https://www.vineyardteam.org/files/resources/Vineyard%20Yield%20Estimation-%20WSU.pdf
Kurtural, S. Kaan and S. Brandon O’Daniel. Crop Estimation
in Vineyards. https://publications.ca.uky.edu/sites/publications.ca.uky.edu/files/ho86.pdf.