A Detailed Guide to the Preparation Method and Application Techniques of Bordeaux Mixture

[Editor's note: Bordeaux mixture is a commonly used fungicide in orchid gardens for preventing and treating fungal diseases. Whether or not fungal diseases occur, orchid gardens can spray it once every 10 days for prevention of fungal diseases.] 1. The fungicidal mechanism of Bordeaux mixture Bordeaux mixture is a protective inorganic fungicide. The so-called protective action means spraying the fungicide on plants before they become diseased, inhibiting or killing fungal spores or bacteria, to prevent the invasion of pathogens and thereby protect the plants. The mechanism by which Bordeaux mixture can kill fungi is that the copper ions in the preparation can exchange with cations such as potassium and hydrogen on the surface of pathogens, causing the proteins on the pathogen cells to coagulate. At the same time, some copper ions penetrate into the pathogen cells and combine with certain enzymes, thereby affecting enzyme activity to inhibit the pathogens. 2. Preparation method of Bordeaux mixture Bordeaux mixture usually has three mixing ratios, and which ratio to use should be determined according to the species and varieties of flowers, in order to avoid phytotoxicity, because different flower species and varieties have different tolerances to lime or copper. (1) 1:1:100 equal-amount formula Bordeaux mixture: 2 kg copper sulfate + 1 kg quicklime + 100 kg water (2) 1:2:100 double-lime formula Bordeaux mixture: 1 kg copper sulfate + 2 kg quicklime + 100 kg water (3) 0.5:0.5:100 equal-amount formula Bordeaux mixture: 0.5 kg copper sulfate + 0.5 kg quicklime + 100 kg water When preparing the liquid, first divide the total amount of water into two equal portions: one portion of water is used to dissolve the copper sulfate, and the other portion is used to prepare the lime milk. When preparing the lime milk, first use a small amount of hot water to slake the quicklime, then use a small amount of water to mix the slaked lime into a paste, and finally add the remaining water and stir to obtain the lime milk. Pour the dissolved copper sulfate solution and the lime milk simultaneously into a third container, or pour the dissolved copper sulfate solution into the settled lime milk (do not pour the lime milk into the copper sulfate solution, otherwise precipitation will occur). Stir while pouring to obtain the sky-blue Bordeaux mixture. Precautions during preparation: (1) The quality of quicklime and copper sulfate should be good. Quicklime should be white, light in weight, and in lump form. Copper sulfate should be pure blue industrial grade. If slaked lime is used, the amount needs to be increased by about 30%. (2) During preparation, both the lime milk and the copper sulfate solution should be cooled to room temperature. After mixing the two stock solutions, a brief stir is sufficient. They should not be stirred for too long, as this affects their suspensibility. (3) The preparation containers should preferably be ceramic or wooden buckets. Metal containers must not be used, because the liquid is alkaline and has a corrosive effect on metal containers. (4) The prepared liquid is alkaline. If it is acidic, more lime should be added. (5) The liquid should be used immediately after preparation and must not be stored for long, otherwise the preparation will produce sediment and affect its efficacy. 3. Application of Bordeaux mixture on flowers (including application on orchids) Bordeaux mixture is low in toxicity to humans and livestock. The liquid adheres to the plant surface and forms a relatively uniform thin film that is not easily washed off by rain, so its effective period is long, reaching about 15 days. Under the action of air, moisture, carbon dioxide, and so on, the preparation gradually releases soluble copper ions, killing pathogens and preventing them from infecting the plant body. In flower applications, its disease-prevention range is broad. It has good control effects on diseases caused by fungi, such as downy mildew, black spot, Phytophthora blight, leaf spot, damping-off, spot blight, anthracnose, seedling blight, leaf curl, and so on. In Guangdong, many flower growers often use it to control black spot on roses. However, Bordeaux mixture leaves white residues on the plant surface, affecting appearance. In addition, ornamental small pumpkins, tomatoes, peppers, grapes, and so on are susceptible to lime damage, so formulations with low lime concentration should be chosen. Some varieties of pear and apple, as well as persimmon, are sensitive to copper, so formulations with low copper sulfate concentration should be chosen. Peach, plum, apricot, and so on are even more sensitive to copper, and Bordeaux mixture is generally not used on them. Also, if there is rainy weather or foggy, humid conditions, Bordeaux mixture should be used with even greater caution, because the release of copper increases, making phytotoxicity more likely. Under high-temperature and dry conditions, it is unsafe for species and varieties sensitive to lime. In addition, it must be noted that Bordeaux mixture generally should not be mixed with other pesticides, and especially must not be mixed with alkaline-sensitive agents. It must not be mixed with lime sulfur, nor used in close succession with it. If preparing Bordeaux mixture is considered troublesome, there are currently several copper-containing fungicide products on the market, such as cuprous oxide (Kao Shan), copper hydroxide (Kocide), basic copper sulfate, copper oxychloride (King Copper, Haobaoduo), copper-ammonia complex, and so on, which can be selected. Their effects are the same as Bordeaux mixture, but they are more convenient to use. The duration of these preparations is generally 7-10 days. (Excerpted from "Flowers" magazine, Guangdong: Long Qingyun, Qi Jialin, Liu Haitao)