May (No. 496)
Post harvest, time to assess trellis
Ben Rose , Performance Viticulture
Real Viticulture is a regular column written exclusively for Grapegrower & Winemaker by Ben Rose, principal consultant of Performance Viticulture. This month’s column is dedicated to assessing trellis systems.
Is it time to re-assess your trellis design and management?
In the current grapegrowing climate, where demand for most grape varieties is low, it is imperative that all growers strive to produce the best compositional parcels of grapes for delivery to the winery. It is a dog-eat-dog industry at the moment and it is no longer sufficient to produce large quantities of grapes at the expense of “quality”. The old adage that quality always sells still holds true, but how do you ensure that the quality you produce is the best you can do, and does not cost you more to produce?
Post-harvest is the time when every good viticulturist should assess his or her management for the season, and determine if inputs have been successful in achieving desired outputs. Canopy management related to trellis design is often thought of as a fixed, rather than variable input. I consider it a variable input and believe viticulturists should be also assessing the performance of trellis during post-harvest analysis.
I am often asked “how can I improve the quality of grapes in my vineyard?” The answer often comes back to the original site selection and trellis design and management.
How does a grower assess the existing trellis system?
There are many checklists published that will provide grapegrowers with a detailed chart of what parameters to assess and within what values the ideal canopy should fall. Many of these assessments should be undertaken during the growing season and combined with pruning weights to give an overall impression.
Most of these checklists look at averages across the vineyard. But growers can also use these checklists to assess specific variation in areas or between cordons (in two-plus cordon systems).
Many trellis systems incorporate a double cordon wire, with the foliage managed differently between cordons. Scott-Henry trellis system (see Figure 1) is a classic example of this, with the foliage from the upper cordon directed upward, and the foliage of the lower cordon directed downward (to reduce vigour). As there is a difference in management between the cordons, they should be assessed separately throughout the season.
Separate canopy assessments of the two cordons in Scott-Henry trellis systems will often reveal lower shoot length, shorter internodes and smaller leaf area, which are the desired results for reducing vigour.
An assessment of grape composition of the two cordons in my experience, however, often leads to the lower cordon producing grapes that are lower in Baumé (up to 1.5Be) and TA and higher in pH, with significant unripe flavours when compared with the upper cordon.
Generally these trellises are mechanically harvested, so the grapes from both cordons are mixed at harvest to produce a load with large compositional variation, which can lead to reduced quality at the winery. (A grower used the example of taking a green banana and a black banana, pureeing them and expecting to get ripe banana flavours: he should have been a winemaker!).
In other vineyards where Scott-Henry trellis is used there may be very little difference between the composition of the grapes from the two cordons; but without the information from careful assessment and post-harvest analysis, we cannot answer the question of “is this the most suitable trellis type for the site?”
The choice of trellis design and management has been often been based on what is already commonly practiced elsewhere in the region, and what yield is required to make a grapegrowing venture financially successful. However, growers now need to move past these criteria and analyse what system they have in place, and how trellis design and management is performing in producing lowest input/highest return grapes.
Information in this article is general in nature and should not be construed as provision of comprehensive advice. Each vineyard site and management situation is different and qualified, specific advice should be sought prior to implementation of any of the ideas discussed in this column.
Ben Rose is the principal advisor of Performance Viticulture. Ben has always been involved in wine and viticulture, growing up on the family’s Rising Vineyard in the Yarra Valley outside Melbourne. He graduated with first class honours in Agricultural Science at Melbourne University and spent four years with Yalumba Wines, as technical officer at Oxford Landing Estate and then as company grower services and nursery manager. Ben established Performance Viticulture seven years ago. Ben can be contacted on phone: 0500 836 773, fax (03) 8660 2238 or email: email@example.com