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A study published on the Oeno One research platform by the State Viticulture Institute in Freiburg has provided clear evidence that the addition of sulphur can improve the effect of copper against downy mildew. Tests carried out in vineyards in southern Germany from 2014 to 2017 and in 2021 showed that copper-based fungicides are effective on leaves but have a rather poor effect on grapes.
Copper has been used to control plant diseases for more than a century. In organic viticulture, copper-based fungicides are the only extensively tested and reliable tools for control. However, they lead to an accumulation of copper residues in the soil. Sulphur is the most important substance for controlling powdery mildew in organic viticulture. In most cases, sulphur- and copper-based fungicides are usually applied simultaneously as a tank mix. For this reason, relatively little was known about the effect of sulphur against downy mildew. The Freiburg study has now investigated this connection.
The results show that the addition of a sulphur-based fungicide to a copper-based fungicide could significantly improve the latter's rather weak effect against downy mildew. In three out of five years, especially in those with high infection pressure, positive effects were observed on the grapes. No further effects were observed on the leaves.
The authors of the study from the State Viticulture Institute in Freiburg point out that the design of this study does not allow an assessment of the effect of sulphur against downy mildew on the grapevine. This would require more detailed laboratory tests. However, the effect of copper fungicides to which sulphur was added was remarkable. However, the reason is still unknown.
(al / Source: oeno-one)