In addition to pest management (as recently posted by Nathan), canopy management is an important consideration in the early post-fruit set period.

While chemical management is of utmost importance in the humid eastern US, where fungal diseases are pervasive, canopy management is a good supplement as it aids in canopy and fruit-zone drying, spray coverage on fruit, and serves the additional role of improving varietal character of grapes and wines.  Thus, canopy management is not an option in the eastern US.

Canopy management considerations in the early post-fruit set period:

Shoot thinning:  It is getting a little late for shoot thinning at this point.  For those in northern regions (PA, NY), who are a bit behind on phenology relative us here in GA: the left photo shows 4 shoots per linear foot of row in a Merlot vineyard inn northern GA; this number is a general target for both open canopies and economic fruit amounts.  The right photo is an example of a nicely thinned Cabernet Sauvignon canopy in northern GA.  Notice the sunlight penetration through the canopy, and the relatively little leaf overlap.  This is a healthy canopy.  For now, anyway….

  

 

Shoot positioning: If shoots are not positioned in a training system, then the vine is not actually being grown using that training system.  What does this mean? If a vineyard is meant to be trained to low, bilateral cordons with vertical shoot positioning but the shoots are falling over between the catch wires and stacking on top of one another, then this isn’t vertical shoot positioning.  Proper shoot positioning within a given training system is critical to optimize the use of that training system – this “use” is usually to intercept light.  Take, for example, the photos below.  This system is part of our research being conducted in Cabernet franc (left) and Petit Manseng (right) in northern GA.  If this “VSP sprawl / y-trellis” system did not have proper shoot positioning, then all of these shoots would be stacked on top of one another and would likely be a mess.  However, care has been taken to make sure shoots grow up each side of the catch wires to permit optimal light interception.  It should be noted that shoot positioning started in these plots three weeks ago.  Had we waited until the post-fruit set period to start shoot positioning, it would have been a lost cause, as shoots would have been too long and tendrils would have already been strongly grabbing neighboring shoots.  The hope with shoot positioning is that the functional leaf area of the canopy is increased, permitting optimal carbon gain and fruit ripening potential.  Shoot positioning also reduces humidity buildup and leaf chlorosis deep within the poorly maintained canopy.

      

 

Leaf removal: This is likely the most important canopy management tool that can be used to change varietal character, and the effect of sunlight on grapes is mostly manifested as positive impact on wine aroma and mouthfeel.  I think back to a varietal character presentation at the 2017 Eastern Winery Exposition by a friend and colleague, Russell Moss, vineyard manager at Domaine Serene.  Sans maybe the petrol character in Riesling, every positive aroma compound  (i.e. norisoprenoids, thiols, terpenoids) was increased, and every negative aroma compound (i.e. methoxypyrazines) was decreased, as a function of greater sunlight penetration into the fruit zones of both red and white varieties.  Above and beyond aroma compounds, research has in many cases shown that exposed fruit contains greater anthocyanins and tannin polymerization, which can result in intensely colored, soft/supple red wines.

Is more sunlight better?  It depends when you remove leaves and what you want to manage in your vineyard.

When: It is getting to be the latest period in which I would intensively remove fruit zone leaves (see photos below showing stages at which I have removed 4-6 leaves in research plots; thanks to Jessica Church for the top right photo).  Waiting much past peppercorn/small pea size berries may result in increase sunburn incidence as berries are not acclimated to the environment outside of the canopy and are then suddenly exposed to the radiation and hot temperatures of late June / early July.  Then again, we have anecdotally observed sunburn manifested in drought conditions – there seems to be a greater risk of grape sunburn when vines are water stressed.  If you haven’t removed leaves before the small pea stage, remove somewhere around 2-3 fruit-zone leaves / laterals from most primary shoots – this will result in dappled sunlight on the fruit  and would improve ventilation and spray coverage.

     

What do you want to manage?: I already mentioned the varietal character improvement with grape sunlight exposure.  Think of shaded, dense canopies resulting in the reduced ability to distinguish between varieties.  To me, it is a great pleasure to taste the dramatic sensory differences between varieties; this can be muted when fruit is shaded and not full of the flavor and aroma compounds that make each variety unique.  As far as diseases go – any pathologist would say that open fruit zones reduce disease incidence and severity.  Re: sunburn risk vs. disease control: is the disease management attained with intensive fruit zone leaf removal worth the sunburn risk? I’ll let you know after this season, my first field season in the most southeasterly state that grows vinifera – Georgia. I will say that I never observed sunburn in Virginia from 2012 to 2016  – when I removed as many as 8 leaves from the fruit-zone in my PhD research.  How about acidity? Increased temperature can reduce grape juice acidity (especially malic acid), an often unwelcome response in the warm-night ripening periods of the eastern US.  From my experiences, there were marginal differences in juice titratable acidity between well-exposed and well-shaded grapes.  This may be because tartaric acid is less affected by temperature and is the dominant acid in grapes when compared to malic acid.  This may also be because both well exposed and shaded grapes are at ambient temperature when the sun is not a factor, such as throughout nights and the many cloudy days of our eastern US growing seasons.  Thus, the difference in temperature between well-shaded and exposed grapes may be attenuated in the eastern US compared to more arid/sunnier regions where radiant grape heating likely occurs with greater frequency.

 

Shoot hedging: This practice indirectly increases fruit zone light penetration, but is also important for reducing canopy self-shading and increasing functional leaf area.  Shoot hedging is an important practice to reduce humidity buildup within the canopy, which will hopefully reduce foliar incidence of fungal diseases such as downy mildew.  Shoots should be hedged before the shoots flop over the top catch wire.  The photos below show the longest shoots should get in a vertically-shoot positioned system before hedging (left) and the same canopies after hedging (right).  The photos show Cabernet franc, a very upright-growing variety; these shoots would have likely been flopped over the top catch wire if it were Merlot or Petit Verdot.  Remember – once apical dominance of primary shoots is broken by hedging, lateral shoot growth will be induced.  Therefore, it is important to keep lateral shoots trimmed back after hedging.

  

 

 

 

Posted in: