18th-century pesticide survives for another year

by Stephen Cadogan

A chemical used for fighting plant diseases since the 18th century has been approved for continued use in the EU by organic farmers, despite the European Food Safety Authority and European Chemicals Agency identifying some risks to farm workers, birds, mammals and soil organisms.

The European Commission and member states have extended once again the authorisation for copper compounds, including copper sulphate, as bactericides and fungicides in organic farming, particularly for potato, grape, tomato and apple production.

Part of the legend behind the age-old copper sulphate pesticide is that it was first used by those who noticed that fields close to copper-smelting factories were not damaged by potato blight.

The plant protection properties of Bordeaux mixture (copper sulphate, water, and lime) were also reportedly discovered by accident, when French winemakers sprayed it on their vineyards to deter thieves from stealing ripening grapes.

Spraying the potatoes with bluestone.

Since 1885, Bordeaux mixture has been used against the potato blight fungus, with the mixture known as “bluestone” well known to Irish farmers, and widely used by them until more modern fungicides became available since the 1940s.

In more recent years, organic farmers here were still using Burgundy mixture (copper sulphate and washing soda dissolved in water), as the only substance permitted for blight control, but they were limited to 6kg per hectare per year, with prior approval from their organic certification body.

Organic farmers are only allowed to use pesticides derived from natural sources, and processed lightly, whereas conventional farmers can also use synthetic substances.

However, there have been question marks over their use of copper sulphate, due to fears about copper’s toxicity, and accumulation in the soil and in organic foods.

The European Commission extended approvals in 2014 for use of copper compounds, on condition that measures were taken to reduce their use, and to allow further environmental assessments to be carried out.

This extension was due to expire last week, pending the results of a monitoring programme.

But in December, the EU’s Standing Committee on Plants, Animals, Food and Feed which has members from the Commission and the member states, extended approvals for one year, although the monitoring programme results have not been published.

Only France and Sweden are believed to have voted against re-approval.

As a result, perhaps the only pesticide celebrated in Irish poetry continues in use.

    Spraying the Potatoes

    (by Patrick Kavanagh)

    The barrels of blue potato-spray,

    Stood on a headland in July,

    Beside an orchard wall where roses,

    Were young girls hanging from the sky.


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