Some people say that Bordeaux mixture can only have a good control effect when the weather is good. What is the reason?

The main component of bordeaux mixture sterilization is basic copper sulfate. Only by changing basic copper sulfate insoluble in water into soluble copper can it play a role in sterilization and treatment. After spraying Bordeaux mixture, the weather is fine, and the amount of soluble copper sulfate dissolved by acidic substances secreted by forest leaves and bacteria is just in line with the amount of copper needed to kill or inhibit bacteria, thus playing the role of sterilization and disease prevention, and will not cause forest phytotoxicity due to excessive soluble copper.

If the Bordeaux mixture is sprayed before the dew is wet in the morning or shortly after the rain, in humid weather, the amount of copper dissolved in the leaf water exceeds the amount needed for sterilization, and at the same time exceeds the amount of copper that trees can tolerate, which is easy to cause phytotoxicity.