How to use Bordeaux mixture as a fungicide for orchids

Bordeaux mixture is a protective fungicide with a long history, strong fungicidal power, wide application and lasting effect. It is made by mixing copper sulfate, lime and water. The prepared Bordeaux mixture is sky-blue, slightly viscous, with stable colloidal precipitation and good suspension properties. When sprayed on plants, it adheres very strongly and is not easily washed off by rain, with a residual effect period of 15-20 days. The main active ingredient of Bordeaux mixture is basic copper sulfate. After being sprayed on the plant surface, under the action of plant secretions, carbon dioxide in the air and organic acids secreted by germinating fungal spores, it gradually releases copper ions. Copper ions can coagulate and denature the protoplasm in fungal cells, causing death. The chemical reaction of Bordeaux mixture is as follows: 4CuSO4·5H2O+3Ca(OH)2---[Cu(OH)2]3·CuSO4+3CaSO4+5H2O Bordeaux mixture is classified according to the ratio of copper sulfate to lime into several types: equal-amount formula (1:1), half-amount formula (1:0.5), double-amount formula (1:2), multi-amount formula (1:3-5) and low-amount formula (1:0.25-0.4). The amounts of copper sulfate, quicklime and water for the equal-amount, half-amount and double-amount Bordeaux mixtures are shown in the following table: ┌─────┬────┬────┬───┬─────────────────────┐ │Formula │Copper sulfate │Quicklime │ Water │Properties │ │ │ (kg)│ (kg)│(kg)│ │ ├─────┼────┼────┼───┼─────────────────────┤ │ Equal-amount │0.5 │0.5 │50 │Can contaminate plants, slow efficacy, no phytotoxicity to plants, strong adhesion│ │Lime half-amount│0.5 │0.25 │5 │Does not contaminate plants, fast efficacy, rarely causes phytotoxicity, strong adhesion │ │Lime double-amount│0.5 │ 1 │50 │Can contaminate plants, slow efficacy, safe, no phytotoxicity, strong adhesion│ └─────┴────┴────┴───┴─────────────────────┘ There are two methods for preparing Bordeaux mixture. One is the two-liquid method, in which copper sulfate and lime are each dissolved in 1/2 of the water, and then the two solutions are slowly poured simultaneously into a third container while stirring, and after thorough mixing, a sky-blue liquid is obtained. The second is the dilute copper and concentrated lime method, in which lime is first diluted with 1/10 of the water, copper sulfate is dissolved in 9/10 of the water, and then the copper sulfate is poured into the lime solution while stirring. Of the two methods, the former requires three containers and is more troublesome to operate, while the latter gives better quality and is simpler to operate. When preparing Bordeaux mixture, the following points should be noted: (1) Metal containers must not be used; (2) It should be prepared and used immediately. After preparation, Bordeaux mixture is sky-blue; if it turns green, it must not be used; (3) It must not be mixed with soap, lime sulfur mixture or rosin mixture; (4) High-quality quicklime should be used; if slaked lime is used, fresh lime should be chosen and the amount should be increased by about 30%; (5) The water temperature should not be too high, and generally it is best not to exceed the air temperature. Bordeaux mixture should be used before disease onset or in the early stage of disease for better results. It can be used to controlorchidanthracnose,orchidleaf blight and many other diseases. (Liu Zhongjian)