EMERGENCE OF INORGANIC PHOSPHONATE RESIDUES IN GRAPEVINE PLANT PARTS, BERRIES AND WINES FROM SOURCES OTHER THAN FOLIAR SPRAYING

Abstract

Inorganic phosphonates are known to effectively support the control of grapevine downy mildew in vi- ticulture. Their application helps the plant to induce an earlier and more effective pathogen defense. However, inorganic phosphonates have been banned in organic viticulture due to their classification as plant protection products since October 2013. Despite the ban, phosphonate has been recently detected in organic wines. Winemakers often assured that they had not applied the fungicide, however, without providing solid proof. This development has fueled the need to better understand potential phosphonate sources and, in particular, phosphonate uptake and distribution in vines. For this purpose, we set up an isolated test field with container vines, allowing to investigate different routes of uptake and the subse- quent mobility of phosphonate over two consecutive years after defined applications. Samples of leaves, stems and berries were analysed by IC-ICP-MS, being validated for quantification of low phosphonate levels therein (LOQs of 0.08-0.15 mg/kg fresh weight). Thereby, grapevines were shown to take up well detectable amounts of phosphonate through the roots, although the total amount found in berries was significantly lower when applying a 0.54 % (w/v) phosphonate solution to the roots (6 mg/kg) than after foliar spray application (38 mg/kg). Furthermore, the determination of the ratios of phosphonate levels in leaves and those in stems allowed identifying whether the vines were sprayed with phosphonate or took up phosphonate through the roots, e.g., from contaminated groundwater. We also present data from open-field vineyards to validate the results obtained with container vines. Besides soil-borne phospho- nate, we also found phosphonate residues in enological additives and processing aids, also contributing to potential phosphonate contaminations in the final wine product. In brief, our contribution will provi- de new insights into the origin of phosphonate in vines and derived wines originating from vineyards that had not been sprayed with phosphonate in the respective growing season.