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GRAPE CROP OUTLOOK 2010 AUGUST

It was warm early this year and remained relatively warm with a few short cool intervals.

One might ask how you make comparisons from year to year and the answer would be a method using Growing Degree Days.

Growing degree days (GDD), also called growing degree units (GDUs), are a heuristic tool in phenology. GDD are a measure of heat accumulation used by agriculturists and scientists to predict the date that a certain growth stage will be reached.

Introduction

In the absence of extreme conditions, such as unseasonable drought or disease, plants grow in a cumulative stepwise manner, which is strongly influenced by the ambient temperature. Growing degree-days take aspects of local weather into account and allow gardeners to predict (or, in greenhouses, even to control) the plants pace toward maturity.

Unless stressed by other environmental factors like moisture, the development rate from emergence to maturity for many plants depends upon the daily air temperature. Because many developmental events of plants and insects depend on the accumulation of specific quantities of heat, it is possible to predict when these events should occur during a growing season. regardless of differences in temperatures from year to year. Growing degrees (GDs) is defined as the number of temperature degrees above a certain threshold base temperature, which varies among crop species. The base temperature is that temperature below which plant growth is zero. GDs are calculated each day as maximum temperature plus the minimum temperature divided by 2 (or the mean temperature), minus the base temperature.  GDUs accumulate by adding each day’s GDs contribution as the season progresses.

GDUs can be used to:

1.     Assess the suitability of a region for production of a particular crop;

2.     Estimate the growth-stages of crops, weeds or even life stages of insects;

3.     Predict maturity and cutting dates of forage crops;

4.     Predict best timing of fertilizer or pesticide application;

5.     Estimate the heat stress on crops;

6.     Plan spacing of planting dates to produce separate harvest dates.

Crop specific indices that employ separate equations for the influence of the daily minimum (nighttime) and the maximum (daytime) temperatures on growth are called crop heat units (CHUs). 

GDD calculation

GDD are calculated by taking the average of the daily maximum and minimum temperatures compared to a base temperature, T_base, (usually 10 °C) (50 degrees F). As an equation:

GDDs are typically measured from the winter low. Any temperature below T_base is set to T_base before calculating the average. Likewise, the maximum temperature is usually capped at 30 °C ( 86 ^oF) because most plants and insects do not grow any faster above that temperature. However, some warm temperate and tropical plants do have significant requirements for days above 30 °C to mature fruit or seeds.

For example, a day with a high of 23 °C and a low of 12 °C (and a base of 10 °C) would contribute 7.5 GDDs.

A day with a high of 13 °C and a low of 10 °C (and a base of 10 °C) would contribute 1.5 GDDs.

10 °C ( 50 ^oF) the most common base for GDD calculations, however, the optimal base is often determined experimentally based on the lifecycle of the plant or insect in question.

GDDs may be calculated using either Celsius or Fahrenheit, though they must be converted appropriately; 5 GDD^C = 9 GDD^F

Please keep in mind that GDD are a rule of thumb that allow us in this application (grape vines) to estimate the occurrence of growth stages - 

As of August 10, 2010 at the NYSAG Experiment Station the Growing degree-days for the 2010-growing season are 20 days ahead of the long-term average.  Now this doesn’t mean that grapes will ripen 3 weeks early.  But it does mean that there is a higher probability than normal that we have the potential for a great vintage.  I think we are very similar at this stage to the 1991 and 2005 growing seasons.  Those years produced stellar wines across the board, reds and whites.

This morning (August 14, 2010)  I took a sample of Aurore that tested 12.4 Brix.  On the 3^rd of August I noticed deer and birds had started sampling our Seyval that had been heavily thinned. I took a small sample of the riper clusters the critters were sampling and found 11.3 degrees Brix.  I took a larger sample of Seyval this morning, (August 14, 2010) again sampling fruit from the riper clusters and got 16.4 degrees Brix!

This is the 14^th of August!  I would guess the true average Brix would be 11-12 degrees, but this is quite remarkable.  Most varieties are well into verasion (véraison) with lignification of canes occurring.   

(Lignification is the hardening off of the canes, going from flesh to wood, maturing, www.thefreedictionary.com/lignification:

   v. lig·ni·fied, lig·ni·fy·ing, lig·ni·fies. v.intr. To turn into wood or become woody through the formation and deposit of lignin in cell walls. ...)

 Verasion (véraison):  A French term used to describe a point at which the grapes start to ripen, becoming soft and starting to change color.

 All varieties are clean and shoot elongation has ceased or slowed significantly in most of our blocks.  We are seeing signs of drought stress in some small areas of a couple of blocks.  We have mowed close and knocked down any weeds in those areas to reduce competition. 

 We like to try different ideas in the vineyard.  When I was in Italy in 1988, I purchased a few books with several research projects in them.  I struggled through a couple of papers and one in particular caught my attention.  The jist or general idea of which was that the carbohydrate sink of most grapevines is at the highest part of the vine.  I thought if that is so, why do we use VSP, which I found to be very labor intensive, especially with varieties that have a procumbent or prostrate growth pattern, like the Pinot Noir clones we had.  In 1995 I decided to train a row I had on umbrella kniffin to a top wire flachbogen system.  After two years, I liked what I saw and we discovered the grapes only needed a shoot positioning around the last week of July.  The fruit was 70-80% exposed.  They started veraision 7-10 days earlier than the other Pinot on VSP.  We didn’t have to mess with catch wires or hedging as the downward growing shoots shut down growth on their own.  We got 1.5-2% riper fruit that tasted better and importantly made better wine.  In 1999 we converted all three rows to high wire flachbogen.  We have achieved 22-24 degrees Brix several years since then.  

We had 3 rows of Gamay Beaujolais (a very upright growing clone of Pinot growing next to our Pinot project.  This grape variety was plagued with crown gall from day one from the nursery.  We had kept them on umbrella kniffin. After the 2004 massacre (see below) we removed the Gamay Beaujolais and replanted with Pinot Noir clones 114 and 115, which are trained to the high wire flachbogen.  

In 2004 a winter back door cold front decimated vinifera and hybrids across the Finger Lakes.  The good news was that the Pinot project survived better than seven other varieties of vinifera in our vineyards with only 12% vine mortality. 

Vine mortality in some of the other varieties we have:

Cabernet Sauvignon  86%

Carmine  35%

Gamay Beaujolais  80%

Chardonnay 55%

Muscat Ottonel 30%

Gewurztraminer 15% 

Riesling 25%

All of the above vines were hilled up in the fall, so the soil protects the renewal zone.  Gewurztraminer has a very active renewal zone and we were able to keep plants going with renewals.  There was no Gewurzt crop for 3 years, though.  

Following the 2004 disaster, the Pinot Noir produced a 60% crop. 

Growing degree days are only an indicator as photosynthesis is negligible in grapes 
below 70^o F and begins to decline above 85^o F. and declines rapidly above 90^o F.  If drought stress enters into the equation, which we are beginning to see in some vineyards in the Finger Lakes, photosynthesis is decreasing at any temperature.  

Growing degree days indicate that we were 20 days ahead of the long term average on August 14, 2010.  If we take all the above into consideration, in reality we may be 10 days or so ahead of the long term average for grape maturity.  This in itself in very significant. 

We will try and use this scenario to increase quality rather than to accelerate harvest. Our dates in the catalog at this point are our best, educated guess.  We will be carefully monitoring pH and taste to determine the proper time to harvest.  

GDD:  August 17, 2010   23 days ahead of LTA (long term average)

 

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www.101winemaking.com 
Tom and Marcy Mitchell
10110 Hyatt Hill    Dundee, NY  14837
Phone: 607-292-3995       E-mail :winemaking@fallbright.com 
Some pictures complements of Steve Shanker    Steve Shanker's Winemaking Lesson site

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Revised: May 01, 2012