A four-year study was conducted to uncover differences in tissue mineral levels related to waterberry (WB) in Thompson Seedless grapevines and to attempt to alleviate the condition. Clusters were dipped into nutrient solutions with no success in decreasing symptoms. The main effect was an increase in symptoms with the diammonium phosphate treatment. Vineyards of varying WB incidence were surveyed, and differences in mineral content of petiole and rachis tissue were noted and correlated with waterberry incidence. Both petiole and rachis levels of total N and NH4-N correlated closely with WB incidence, and K rachis levels tended to be lower in the WB symptom samples. Ca and Mg levels did not vary with incidence. In three years of N, P, Ca, and Mg fertilizer trials in vineyards of varying WB susceptibility, the following effects were noted: N and P petiole levels generally increased with N and P treatments, respectively; petiole K was significantly reduced in one location, apparently as an effect of N fertilization, and Ca and Mg treatments did not consistently increase petiole levels of Ca and Mg. None of the fertilizer treatments decreased WB. However, N fertilizer increased WB in some locations, particularly those with histories of low WB incidence and low N fertilization. Regression analysis of all Thompson Seedless rachis mineral analyses, 1979-1982, showed significant correlation only between total N and NH4-N levels and the occurrence of symptoms. WB symptoms were observed at total N levels of approximately 1.5% and higher and NH4-N levels of 3000 ppm and above in rachis tissue.
- Copyright 1985 by the American Society for Enology and Viticulture