ISHS Acta Horticulturae 206: Symposium on Grapevine Canopy and Vigor Management, XXII IHC
EFFECTIVENESS OF SHOOT TOPPING AND LEAF REMOVAL AS A MEANS OF IMPROVING QUALITY |
| Author: | W. Koblet |
| Abstract:
Under our climatic conditions the vines continue their growth until fall. Fruit maturity occurs relatively late and the grapes often rot before they are ripe. An appropriate canopy management is therefore an important aspect of our viticultural practice. During the past years many investigations focussed on summer pruning, shoot positioning and leaf removal in the cluster area. Kliewer (1982 a, b) published an extensive literature review about cultural practices to improve the interception of solar radiation. Koblet (1985) also reviewed the recent studies and discussed them in view of his own findings. Smart (1982, 1985 a, b) and Smart et al. (1982) recognized that canopy attenuation affects many microclimatic elements. The largest microclimatic difference between dense and sparse canopy occurs in radiation flux densities. Optimal trellising and canopy management are also discussed by Carbonneau (1985) with the lyre trellis system. Already Shaulis et al. (1966) showed the full benefits of a double curtain type canopy. Kriedemann (1977) studied intensively the photosynthetic activity of the vine leaves as influenced by aerial and internal factors. General leaf removal studies were carried out by Kliewer (1971). He pointed out that severe leaf removal caused lower yield and quality. Carbonneau (1980) and Carbonneau and Huglin (1980) studied the leaf-fruit-microclimatic equilibrium in relation to training systems. Late removal of leaves in the cluster area is in general desirable to enhance berry coloring and to reduce bunchrot and acidity. Early leaf removal - prior to blossom time - should be avoided. Coombe (1962) and Koblet (1966) found a close correlation between leaf area and fruit set. Removal of basal or interior leaves in a later stage leads to better aeration of the clusters and hence decreases Botrytis. Grapes well exposed to the sun contain less malic acid and more sugar (Ruffner et al. 1975, Koblet et al. 1977). We also demonstrated that basal leaves cease in fall their carbohydrate export whereas young leaves remain active (Koblet and Perret, 1979). Young and rapidly growing leaves on the other hand show first a strong import of carbohydrates. With further leaf development there is a continued increase in photosynthetic activity. According to Kriedemann (1977) young leaves produce more organic acids, and mature leaves more sugar. Pandey and Farmahan (1977) found also an increase of the photosynthesis up to the fourth week after anthesis and thereafter a decline until harvest. Similar results are reported by Alleweldt et al. (1982) and El-Sese (1983). | |
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