Crop Estimation in 2012
Hans Walter-Peterson, Finger Lakes Grape Program
Dr. Jodi Cresap-Gee, Lake Erie Regional Grape Program

Estimating a crop every year is often a real challenge for grape growers no matter where they
farm, but here in the East our variable weather conditions and their impacts on vines, clusters
and berries make the challenge that much more â?? uh, challenging.
In many cases, crop estimation is used to determine how much, if any, fruit should be removed
from the vines in order to reach a real or perceived quality target. So it is no wonder that we will
see more growers trying to estimate their crops in cool years or seasons with an unusually
heavy crop when ripening can be a challenge.
However, neither of those conditions really exists in 2012 in the Finger Lakes or the Lake Erie
region. Many blocks with Concord, Niagara, Baco, Chardonnay and other early varieties got hit
with frost damage to varying degrees this spring, reducing potential yields. In addition, we are
experiencing another warmer than average growing season with bloom occurring 2-3 weeks
ahead of time, which means we should have ample growing season to ripen an above average
crop (for those who have one).
So why should growers bother estimating their crop this year?
Two reasons come to mind: facilitating good communication with current buyers, and
determining the need to find new buyers if necessary. And for crop insurance purposes, if need
be (OK, three reasons to do crop estimation). Buyers will want to know as soon as possible if
there will be enough fruit to fill their needs come harvest, or if they need to go out and find more.
Growers who can provide that kind of information to wineries and processors earlier in the
season can potentially benefit from an improved reputation and relationship with buyers, making
them a more highly desired supplier of fruit. Or at the other end of the spectrum, growers will
want to know if they need to go out and find more buyers for their crop if it is larger than what
they have committed to buyers so far.
Adjusting crop size. To maintain balanced vines, one must attempt to maintain the appropriate
leaf area to fruit weight ratio, which, according to Dr. Terry Bates with the LERGP, is 15 cm2 of
exposed leaf area/gram of fresh fruit.
? Does this ratio apply to wine grapes? Of course â?? wine grapes need to be balanced to
attain the quality desired by the winemaker.
? Does this ratio apply to processing grapes? Yes! While the goals of growing processing
grapes (maximum tonnage) differs from that of wine grapes (maximum quality), vines
are healthiest and most consistently productive when they are balanced.
? How can a vineyard manager work toward this goal? Using strategies such as pruning,
fruit thinning, shoot thinning, and combinations of these techniques will all alter the crop
size, which will affect crop quality. Of course, this assumes good insect, disease, weed,
and nutrient management programs are in place.
In wine grape production, the goal is often to reach an optimal balance of sugar, acidity,
color, etc. in specific varieties. Although the definition of â??ripeâ?? is changing with new
research, for simplicityâ??s sake, we will focus on ?Brix. To ripen a wine grape crop to about
21? Brix, the crop weight MUST NOT exceed the leaf area, or vines will struggle to ripen the
crop, and wine quality will be compromised, not to
mention that vines with excessive crop loads tend to
over-winter very poorly.
? Strategies to manage crop load and canopy in
wine grapes:
o Pruning
o Shoot thinning
o Leaf pulling
o Crop estimation and thinning
o Vigor management
o Soil/nutrition management
In processing grape production, the goal is often to reach a specific level of ?Brix at
maximum yield. To ripen a crop to about 15-18 ?Brix, the crop weight MUST NOT exceed
the leaf area, or vines will struggle to ripen the crop, and juice quality will be compromised,
not to mention that vines with excessive crop loads tend to over-winter very poorly.
? Strategies to manage crop load and canopy in juice grapes:
o Pruning
o Shoot thinning (Figure 3)
o Crop estimation and thinning
o Vigor management
o Soil/nutrition management
Notice any similarities? Keep in mind that many of the management practices in wine and
processing grape production are very similar, with the main difference being scale of production.
Crop estimation â?? in either production system â?? requires historical data from previous years and
average cluster weights when berries are at approximately 40-50% of their final berry weight.
This is at 30 days post bloom in Concord production and at about 1200 growing degree days
(50?F base) for hybrid and vinifera grapes.
As we all know, the growing season got off to an early start in March. Both the Finger Lakes and
Lake Erie regions reached 1200 growing degree days (GDDs) earlier than we usually do in the
season, if you include the GDDs that we accumulated in March. While it isnâ??t unusual for us to
accumulate a few GDDs in March, this year was obviously different as it was warm enough to
begin vine growth (news flash - grapevines donâ??t pay attention to the calendar). Therefore, it
makes sense that we would include those early GDDs this year if using this method to estimate
crop yields.
As we have discussed and demonstrated a number of times over the past several years, we
have a pretty good handle on how to do crop estimates in Concord. Based on work by Terry
Bates, Bob Pool and others, we know that Concord berries are at about 50% of their final berry
weight at 30 days after bloom, which happens to generally coincide with about 1200 GDDs here
in New York. Estimates can be done later in the year, all the way until veraison, as long as
adjustments are made to the factor to convert current berry weight to final berry weight. While
the numbers might be a bit different, you can probably use the same technique and information
to get a pretty good estimate of a Niagara or Catawba crop as well.
Crop Estimation


Table 2 (pdf; 76KB)