Formalin (formaldehyde) can be used as a fungicide for orchid cultivation

Formalin is a colorless, transparent liquid that can be mixed with water and ethanol in any proportion. Its aqueous solution shows a weakly acidic reaction. The formaldehyde aqueous solution volatilizes easily at room temperature and can corrode iron containers. During long-term storage, it polymerizes into a white precipitate and is toxic to humans and livestock. Formaldehyde has a strong sterilizing effect and also acts as a fumigant. It is mainly used to treat seedlings, soil, and for greenhouse disinfection. Generally, it cannot be used as a foliar spray. To treat seedbeds and greenhouse soil, use 2 kg of a 50-fold dilution or 4 kg of a 100-fold dilution per square meter. When the soil is moist, use the 50-fold dilution. If the soil does not have strong water absorption capacity, it can be applied in two separate applications to prevent loss. After application, cover the soil surface with rice straw or plastic film to maintain the effectiveness. After 1 to 2 weeks, once the formaldehyde has completely volatilized, plant to avoid damaging the roots. Points to note during use: (1) After formaldehyde forms a white precipitate, it is likely to cause phytotoxicity to plants. Once precipitation occurs, immerse the bottle in water for several tens of minutes until the white precipitate disappears; (2) Formaldehyde vapor is toxic to humans and livestock and must not be inhaled, and hands contaminated with the solution must not be used to rub the eyes. (Liu Zhongjian)