Blue is the colour of my true love's ... grapevine??

There are big differences between growing grapes here in Ontario versus good 'ol New Zealand. When you move from one place to another, sometimes they stick out like a sore thumb.

Case in point: Off-colour grapevines. Driving around Niagara you may come across vines looking like the picture on the right.

This rather sickly shade is from a copper and lime solution, called Bordeaux Mixture by some, that is applied to the vines to keep diseases at bay. For grapes, it is an effective control for Powdery Mildew and Downy Mildew, but it is used in a wide variety of crops for fungal and bacterial diseases. See this UC Davis page for more information.

The history around Bordeaux Mix is worthy of discussion, and was included in the book my Dad and I wrote (<shameless_plug> Grapes, published by CAB International, and available at a variety of bookstores, including Amazon.com </shameless_plug> ):

"Downey Mildew, imported with the American Grapevine material that was used to combat Phylloxera, was first reported in France in 1878 and caused another downturn in French grape production until a control method was found. The story goes that a grower just outside the village of Bordeaux was having trouble with townspeople stealing grapes as they walked by his vineyard (Prial, 1987). He decided to paint the clusters near the road with a greenish-blue paste made by mixing copper sulfate and lime, which gave the leaves and fruit and unappetizing splotchy green-blue colour. It is not reported if this deterred the pilfering, but a passing scientist observed that the grapes did not develop Downy Mildew. A few enquiries and experiments later, in 1885, he published resutls that showed the effectiveness of this bouilli bordelaise (Bordeaux mixture), and it is still used around the world for control of Downy Mildew as well as other disease organisms."

Bordeaux mix is approved for use in Organic and Biodynamic growing as well, and it is an important tool to being able to control Downy Mildew in particular in those systems, as Powdery Mildew can also be controlled with sulfur.

One issue with its use is that it does add copper to the soil, so with long term application (decades and decades) to the vines, the amount of copper in the soil can get too high, resulting in less productive vineyards. So like anything else, it must be used with intelligence and restraint.

Winegrowers are well aware of the challenges of using Bordeaux mixture and use it as only a part of a well-designed disease management programme.