The effect of leaf removal on canopy microclimate, vine performance and grape phenolic composition of Merlot (Vitis vinifera L.) grapes in the continental part of Croatia

Leaf removal in the cluster zone is one of the commonly applied viticultural practices used to increase light penetration and to decrease humidity in dense foliage. A two- year study (2018/2019) was carried out on the Merlot variety grown in the vineyard on the Croatian hillside with continental climatic conditions, to study the effects of basal leaf removal on canopy microclimate, grape chemical composition and vine production. Leaf and lateral shoot removal was performed at berry set. Meteorological data were recorded together with microclimatic measurements: air temperature, UV radiation and relative humidity in the fruiting zone. Leaf removal altered microclimate by increasing the UV radiation within the cluster zone. Sugar concentration, bud fruitfulness and yield performance was not affect by the treatment, while leaf removal significantly reduced the concentration of titratable acidity in berry samples and increased the concentration of phenols, anthocyanins, flavonols and flavan-3-ols in berry skin. Leaf removal had a higher influence on the grape anthocyanin and flavonol composition in a season with the cooler berry ripening conditions. These results revealed important difference in leaf removal efficiency on phenolic composition of the grapes in different seasonal climatic conditions during ripening.