Effect of Shading on Bud Necrosis and Bud Fruitfulness of Thompson Seedless Grapevines

¹ Departamento de Fruticultura y Enologia, Facultad de Agronomia, Pontificia Universidad Catlica de Chile
² Department of Viticulture and Enology, University of California, Davis, CA 95616

Both localized shading of individual buds or shading entire shoots with neutral shade cloth resulted in a 60% to 500% increase in the number of buds showing necrosis in Thompson Seedless vines grown under field conditions in Chile. Primary buds showing necrosis usually did not burst, resulting in either `blind buds' or `split buds'. The amount of bud necrosis and bud fruitfulness that developed at individual artificially shaded nodes were not influenced by the presence or absence of the primary leaf, cluster(s), or lateral shoot, provided these structures did not cause significant shading of the buds themselves. A period of 15 days of shading of individual buds or entire shoots at photosynthetic photon flux density (PPFD) less than 1% to 2% of full sunlight was sufficient to significantly raise bud necrosis above that of non-shaded control vines. Longer periods of shading did not significantly increase the amount of bud necrosis. Enhancement of light penetration within the canopy of grapevines by shoot positioning or by shoot thinning after berry set significantly reduced the amount of bud necrosis and increased bud fruitfulness.

Key words: bud necrosis, bud fruitfulness, blind bud, split bud, shading, canopy management, table grapes

Submitted on March 10, 1989

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