Temperature management has a direct impact on fruit quality. According to Bonada et al. (2015), high temperature may affect the degree to which water deficit can produce colorful and flavorful wines rich in phenolic compounds. As such, high temperature may ruin a careful vineyard management of water deficit throughout the season with just over a few days before harvest.
Temperature management can be accomplished in a number of ways including canopy manipulation, which is what we are going to discuss today. This blog post reviews the effects of early season microclimate manipulation through leaf removal.
First of all, it is important to have in mind that key considerations for leaf removal strategies include careful timing and intensity as reported by Smith and Centinari.
Mechanical leaf removal in a Riesling vineyard (source)
Second, we can take into account results recently documented in the following studies.
Komm et al. (2015) studied the effect of different timings of leaf removal on fruit composition for Riesling and Sauvignon Blanc relative to no removal. For the treatment groups, the researchers performed complete removal of all leaves and lateral shoots in the fruit zone on both sides of the canopy at pre-bloom, bloom and four weeks post-bloom.
No negative implications were observed in total fruit set in either year. In 2013, pre-bloom leaf removal in Riesling increased terpene concentrations in the harvested juice. In 2012, post-bloom leaf removal in Riesling reduced concentration of acids below those of the pre-bloom treatment in juice.
Moreno et al. (2015) looked at the impact of defoliation before flowering on anthocyanins, flavonols and flavanols for Tempranillo in Spain. The treatment did not significantly alter the concentration of total anthocyanidins, but increased total flavanols and flavonols in season-specific ways. According to the authors, the higher concentrations of compounds can form copigments with anthocyanins, and thus improve wine color stability or tannins sensorial properties.
Cook et al. (2015) studied the interaction of leaf removal timing and different deficit irrigation schemes on productivity and fruit composition for Merlot in central California. The authors found that leaf removal treatment increased anthocyanin concentration and had no impact on yield. Interestingly different irrigation treatments made no difference on anthocyanin concentration.
Pre-bloom leaf removal is an important and strategic practice to manage fruit microclimate.
It can enhance flavors for white varietals and improve anthocyanin concentration for red varietals.
Before attempting this tactic, vineyard managers should assess potential risks and rewards as below:
- Light exposure in the cluster zone should be good at the early stage of fruit development (ie. light penetration to be around 20% of PAR).
- Exposure to high temperature is bad in the late season.
- Keep in mind there are no reported benefits if berry acclimation is post fruit set (i.e. pre-bloom removal is more effective).
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