University of Vermont

By Terence Bradshaw

As harvest approaches, it is critical to track ripening in the vineyard to best achieve the juice chemistry values to optimize wine quality. Sampling should be methodical and regular (at least weekly, or more often as harvest approaches). Generally a 100 berry sample is sufficient to ascertain general ripeness. Berries should be randomly selected, but should come from a diverse distribution in the vineyard: from all parts (top, shoulder, bottom) of the cluster, and from clusters well-distributed through the canopy. Fruit can be collected into a plastic bag, crushed lightly, then a corner of the bag cut off to squeeze juice into a sampling jar. Juice should then be assessed for pH, sugars, and titratable acidity (TA). Remember that for most popular cold climate grapes, TA is a primary determinant for ripeness; for reds (Frontenac, Marquette), a target TA of 1.5% or lower is preferred; for whites, 1.2% should be considered the upper end, although La Crescent may frequently have higher values. Ideally, all grapes for winemaking should have TA below 1%, but that is not always possible for the cultivars that we grow. Work with any wineries you plan to sell grapes to to determine their preferred juice chemistry levels before harvest.

Juice chemistry tracking for cultivars in the UVM vineyard may be found at: http://www.uvm.edu/~fruit/grapes/uvmvineyard/2016UVMfieldtesting.pdf

A primer video on evaluating grape ripeness may be found at: http://www.extension.umn.edu/food/small-farms/crops/knowing-when-to-harvest-your-grapes/

Dr. Imed Dami at Ohio State has a good fact sheet on evaluating grape ripeness at: http://ohioline.osu.edu/factsheet/HYG-1436

Sugar level and pH are easily evaluated with simple tools (a refractometer and pH meter, respectively) available from most winemaking supply outlets. TA test kits are typically available from the same vendors. A procedure for measure TA through titration is available at: http://www.extension.iastate.edu/wine/titratable-acidity

By Terence Bradshaw

August 15, 2016

Grapes are at or near veraison in Vermont vineyards, which signals the start of fruit ripening. This is an important time of year for a few activities. First, bird damage can be expected to begin and increase as fruit ripen. Birds will harvest your berries just a day or two before you’re ready to, so if you don’t have damage yet, don’t think you’re out of the woods. Netting is the best method of protection. Auditory scare calls, propane cannons, and inflatable ‘used car lot’ balloons are sometimes used as well, but their effectiveness is questionable and their annoyance factor significant. Dr. Alan Eaton from the University of New Hampshire wrote a good guide on prevention of bird damage in fruit plantings, available at: https://extension.unh.edu/resources/files/Resource001797_Rep2514.pdf.

Now is the time for plant tissue testing as well. Petiole samples may be collected at bloom or veraison, and comparisons between years or blocks should be based on the same time of collection.

Samples should be collected separately for each cultivar or block. In each sample, a random collection of 75-100 petioles should be collected from throughout the planting. Petioles should be collected from the most recent fully expanded leaf on the shoot, not across from the fruit cluster as is collected for a bloom sample. Just remove the whole leaf and snip the petiole (the leaf ‘stem’ off with your pruners. Gently wash each sample in water with a drop of dish detergent, then rinse fully and place in an open-top paper bag to dry. The closest analytical lab for grape petiole analysis is the Cornell Nutrient Analysis Laboratory . Please note that they now have partnered with Agro-One Services. It is recommended that you contact them before you send any samples to confirm that recommendations will be sent along with the analysis and to confirm costs.
Video about petiole sampling: https://www.youtube.com/watch?v=8EHbojLfXek

Start making plans for harvest and crush now. This may be a good time to thin out any lagging ‘green’ clusters that developed from secondary buds and are lagging in ripeness. Remember, you’re looking for crop uniformity. You can estimate yield by counting clusters on a few representative vines and multiplying by the typical cluster weight for your vineyard. If this is unknown, use 0.25 pounds (113 grams) per cluster, which is the average we have recorded at the UVM vineyard for Minnesota cultivars from 2010-2015. Your formula should look like this:

Estimated tons/acre = average # clusters/vine * 0.25 lbs/cluster * # vines per acre /2000 (pounds per ton)

For the UVM vineyard, where we have 726 vines per acre [43560 sq feet/acre / (6 feet between vines * 10 feet between rows)] = 726, the crop estimate for 50 clusters per vine is:

4 tons/acre = 50 * 0.25 * 726 / 2000

Four tons per acre is a good crop for mature, healthy vines for most cold climate cultivars; some vigorous vines in good health may support higher crop yield but I wouldn’t push mush more than 5.5 tons per acre lest you compromise ripening. If you have too many clusters, thin out the smallest and greenest ones to get your target cluster number. This exercise will help you plan lugs, bins, and tank space, as well as allow you to communicate that information to any wineries you plan to sell to.

http://northerngrapesproject.org/wp-content/uploads/2016/08/July-2016-News-You-Can-Use-canopy-mgmt-and-exposure.pdf

 

 

 

News You Can Use

Canopy Management and Light Interception

July 2016

Shoot tipping and basal leaf removal in Frontenac training systems trials in Clayton, NY.

(photo by T. Martinson).

Canopy management involves manipulation of vine growth to achieve production goals such as optimizing light interception, managing disease pressure, adjusting cropping levels or maximizing fruit quality. Site selection, grape variety, training system, soil fertility, and water management will all influence the amount of canopy management needed throughout the season. However, canopy management is labor intensive, so it is important to understand the costs and benefits associated with these practices. Mike White and Tim Martinson covered various canopy management practices, and the economics of them, in the February 2012 Webinar “Nuts and Bolts of Canopy Management.”

As canopy management affects light exposure to the clusters, this month we will also review the work being done in Clayton, NY, looking at the difference in fruit chemistry between shaded and exposed clusters of Marquette and Frontenac. In short, clusters exposed to sunlight have lower titratable acidity and higher soluble solids at harvest than clusters that are shaded. A research report from the Year 4 Northern Grapes Project Progress Report has complete details.

February 2012 Webinar “Nuts and Bolts of Canopy Management” http://youtu.be/eBGfmsSVJsM

Research Report “Impact of Shading on Frontenac & Marquette Fruit Composition” http://northerngrapesproject.org/wp-content/uploads/2016/02/NY-shaded-vs-exposed-Year-4.pdf

Additional Info: 2016 Preliminary Results. This year we are looking at ways to increase light interception by using a rake wire and “downward shoot positioning,” along with cluster-zone leaf removal, on high cordon-trained Frontenac at Clayton. The two-factor experiment involves:

1. Use of a rake wire to constrain canopy (Y or N)

2. Shoot combing and/or leaf removal in the cluster zone.

Rake Wire: Two moveable wires on each side of the canopy were used to constrain the canopy downward. They were at the top of the canopy at the start of the season and were moved down, with shoots tucked behind them, as the season progressed.

Last week we used a light meter to compare ambient light to the light reaching the cluster zone in this experiment. Preliminary results showed that shoot combing + the rake wire resulted in elevated light exposure – the range of values indicated by box plots below being similar to the “Rake Wire + Leaf Removal” treatment. Compare to the ‘no rake wire’ values at the left.

W

e will collect samples to compare fruit composition under these treatments this fall.

The Northern Grapes Project is funded by the USDA’s Specialty Crops Research Initiative Program of the National Institute for Food and Agriculture, Project #2011-51181-30850

Chrislyn A. Particka, PhD

Extension Support Specialist

Cornell University

School of Integrative Plant Science, Horticulture Section

630 W. North Street

Geneva, NY 14456

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www.northerngrapesproject.org