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Significance

Grapevines are one of the most widely grown fruit crops in the world with significant plantings in Europe, North and South America, South Africa and Australasia. Grapes are used in the production of wine, brandy, or non-fermented drinks and are eaten fresh or dried as raisins.

In an effort to control a root-feeding aphid called Phylloxera, resistant grape rootstocks were introduced to Europe from North America in 1878. At the same time, the downy mildew pathogen was introduced into France, probably as oospores on the imported rootstocks, and spread widely throughout Europe. In 1885, P.M.A. Millardet (Figure 12) first used Bordeaux mixture to control downy mildew. It is said that a farmer had applied this mixture of copper sulfate and lime to produce a chemical residue on grapes along the roadside to discourage pilfering by passersby. Millardet's extensive experimentation led to the development of Bordeaux mixture as the first widely used chemical to protect plants from fungal infections. His description of this work has been translated into English as a Phytopathological Classic and is cited in the references. A statue of Millardet was erected in a park in Bordeaux to express the gratitude of the French people for his important discovery. Bordeaux mixture remains an important fungicide even today.

Figure 12
(click on image for more about the history
of Millardet and Bordeaux mixture)

Downy mildew is a highly destructive disease of grapevines in all grape-growing areas of the world where there is spring and summer rainfall at temperatures above 10º C (50º F). Crop losses in individual years can be 100% if the disease is not controlled during favorable weather. Early infection of young bunches can lead to significant crop loss, whereas, severe leaf infection affects the source-sink relationship in the vine and may lead to defoliation and possible sunburn or lack of fruit ripening. This destruction of leaf tissue may affect sugar accumulation and growth in the subsequent season (Figures 13 and 14). Currently, there are no suitable sources of resistance in commercially acceptable varieties, so fungicides are the primary means of disease control.

Figure 13

Figure 14

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