Changes in Elemental Sulfur Residues on Pinot noir and Cabernet Sauvignon Grape Berries During the Growing Season

¹ Department of Plant Pathology, University of California, Davis, CA 95616
² Viticulturist, Beaulieu Vineyard, Rutherford, CA 94573
³ Cooperative Extension DANR Analytical Lab, University of California, Davis, CA 95616.

Elemental sulfur residue on grape berries was determined for a Pinot noir vineyard in the Carneros region and a Cabernet Sauvignon vineyard in the Oakville area of Napa County, California. Each vineyard was divided into four quadrants. Each quadrant received two or three wettable sulfur applications prior to bloom, followed by scheduled applications of either elemental sulfur dust, triadimefon (Bayleton), fenarimol (Rubigan), or myclobutanil (Rally) according to label instructions. Residual elemental sulfur levels were determined at two-week intervals (5 sample dates) from the day after final sulfur dusting until harvest using an inductively coupled plasma spectrophotometer (ICP). Immediately after the final dusting, residual sulfur levels were 7.9 and 13.6 µg/g berry weight and decreased rapidly to 3.0 and 2.3 µg/g berry weight for the remainder of the season for Cabernet Sauvignon and Pinot noir, respectively. Residues for grape berries which were not dusted were significantly less (p = 0.05, Duncan's multiple range test) and ranged from 2.5 to 0.2 and 3.1 to 0.5 µg/g berry weight for Cabernet Sauvignon and Pinot noir, respectively, for most sample dates. In comparison, 16 other vineyard blocks with differing final sulfur dust applications were sampled at harvest. Residual sulfur levels ranged from 0.9 to 2.7 µg/g berry weight.

Key words: Vitis vinifera, grape, fungicide residue, elemental sulfur

Submitted on July 6, 1992