Taking an environmentally sensitive approach to pest management
Berry splitting or cracking is a physiological disorder that contributes to fruit loss of table and wine grapes. It often occurs in Missouri when rainfall follows a period of very dry weather. After grape skins split, pathogens can easily enter and infect the exposed pulp (Figure 1).
The degree of berry splitting is dependent upon several factors, including the cultivar, stage of berry development, and climatic factors. It does not seem to be related to berry size or skin thickness. Concord and Zinfandel are two of the more susceptible grape cultivars to berry cracking, while Villard blanc is relatively tolerant.
Berry development occurs in three growth phases. The first phase occurs after pollination when berries are rapidly enlarging by cell division and enlargement. This phase usually lasts for three to four weeks. The next phase, known as the lag phase, occurs for about two weeks. Little berry growth occurs during this time, but organic acids increase in the fruit. Several changes occur in berries during the third stage of growth, including rapid fruit enlargement, the accumulation of sugars, a reduction in organic acids, and red color development of skins. Berry cracking typically occurs during phase three.
Grapevines are susceptible to berry cracking when grapevines are water-stressed. When heavy rainfall or irrigation occurs after a drought, berries will often split. During drought, the skin of berries hardens. When moisture occurs on the berry surface, water then diffuses through the skin into the interior of the fruit. The rapid influx of water into the berry, especially when temperatures are high, results in cracking.
When berries crack, the skin cells rupture and the internal flesh of the grape is exposed. The fungal pathogen, Botrytis cinerea can then infect the fruit and cause bunch rot. This disease alters fruit flavor and adversely affects wine quality even when disease infection is low (3% or higher).
To limit berry splitting, use proper irrigation management practices that minimize water and nutritional stresses. Optimal levels of calcium in grape tissue, assessed by tissue analysis, results in the development of thicker epidermal and sub-epidermal cell wall layers in berries, which helps them resist cracking when environmental conditions are conducive to splitting. Additionally, a disease control program that limits Botrytis infection will also minimize fruit loss that occurs after berry splitting.
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REVISED: August 22, 2019