Bordeaux Mixture
Aiton's Encyclopedia (1910)
Important: Safety Warning
This page recommends pest-control substances such as arsenic compounds, strychnine, or cyanide — in some cases applied to food crops. These substances are lethal to humans and animals, and their use is now banned or strictly controlled.
This information has been left in for historical purposes but should not be acted upon.
a liquid much used for spraying plants. The name is due to the early use of the mixture by members of the Academy of Science at Bordeaux, France. It was found about 1880 that copper sulphate, or blue vitriol, had the virtue of killing mildew and other parasitic growths on grape-vines. The use of the mixture spread from the grape growers of France to Germany, Spain, Italy, England, and other countries, both of the Old World and the New, until Bordeaux mixture has come into general use among florists, fruit growers, and gardeners as a preventive of mildews, rusts, scabs, etc. Growers of peaches spray before the buds open to kill all spores. Potato growers spray their vines to keep the leaves from rusting. The mixture is a general remedy for the fungous plant pests that infest the garden and orchard, just as paris green is the foe of corresponding insect pests. Although the use of the mixture is recent, farmers' clubs and granges, as well as large growers of potatoes, now order blue vitriol by the car load. One writer recommends the following method of preparing the mixture: Blue vitriol dissolved in water, warm, even hot water is best, 6 pounds; slaked lime dissolved in water and strained, 3 1/2 pounds; water, 50 gallons. Shake thoroughly. The mixture may be applied wastefully with a whisk broom or a watering pot, but the proper way is to use some sort of a syringe or force pump provided with a spraying nozzle. See Spraying ; Paris Green
What Has Changed in the Last Century
Aiton's 1910 recipe — six pounds of blue vitriol, three and a half of slaked lime, fifty gallons of water — is essentially the mixture still sold today, and the spraying regime for potato blight and vine mildew has not fundamentally altered. What has changed is its standing: Bordeaux mixture is now one of a handful of fungicides allowed under organic certification, while its companion in the entry, paris green, was withdrawn as an arsenical poison. The catch is that copper, unlike an organic pesticide, never degrades; it builds up in soil, and the European Union has capped copper applications at a few kilograms per hectare per year to slow the accumulation in old vineyards. Modern accounts also credit the discovery to Pierre-Marie-Alexis Millardet at Bordeaux in the 1880s, who noticed that vines daubed with copper and lime to deter thieves had escaped downy mildew.
Written for this edition, 2026.