Grape berry splitting is not limited to humid climates
In dry climatic regions, precipitation is limited during the growing season, and the relative humidity is low. Splitting exposes the flesh cells of grape berries to the dry air and leads to dehydration. The incidence of berry splitting in dry regions may be underestimated due to the shrivelled appearance of split berries. Absorption of rain water across the berry surface seems not to be the only pathway causing berry splitting. Instead, we observed cases that are not directly related to rain-induced splitting in arid eastern Washington. The berry splitting severity was 20% in a Concord vineyard that was drought-stressed before veraison, but only 1% in the non-stressed portion. In an irrigation study with Concord, the splitting severity was slightly higher when irrigation water was applied at 50% of vineyard evapotranspiration (ET) compared with 100% ET, but only if the water deficit was relieved at veraison. However, we did not observe a similar effect in Cabernet Sauvignon irrigated at only 25% ET before but not after veraison. These results suggest that water deficit may increase the susceptibility to berry splitting in vulnerable cultivars. In another case, we observed berry splitting in field-grown 'Zinfandel' but not in 'Merlot' in multiple seasons. In addition to its weaker skin, the tight clusters and large berries of 'Zinfandel' contributed to berry splitting, whereas cuticle thickness could not explain splitting susceptibility. Correlation analysis indicated one berry per mm length of rachis is the critical cluster compactness to induce splitting in 'Zinfandel'. These results demonstrated that absence of rainfall is not sufficient to prevent berry splitting. Awareness of the factors involved in berry splitting is still necessary for growers in arid regions.
Chang, B.M., Zhang, Y. and Keller, M. (2020). Grape berry splitting is not limited to humid climates. Acta Hortic. 1276, 155-162
water deficit, drought stress, regulated deficit irrigation, cluster compactness