Seed-treating Materials

chemical substances used to disinfect seed. Their primary purpose is to protect plants from infection by pathogenic microorganisms at the beginning of growth and development.

Seed-treating materials must have disinfectant and protective action. The disinfectant action, that is, the ability to destroy such agents of infection as spores, mycelium, and bacteria, is manifested at the moment of treatment. The protective action occurs in the soil, where the treating materials create a zone that protects the seeds and sprouts against mold and infection by root rot.

Substances most commonly used as seed-treating materials are fungicidal, for example, tetramethylthiuram disulfide (TMTD) and hexachlorobenzene, or bactericidal, for example, copper trichlorophenolate. Some seed-treating materials, such as the mercury-containing granozan (C₂H₅HgCl) and Panogen, kill pathogenic fungi and bacteria at the same time.

Seed-treating materials may also combine fungicides or bactericides with insecticides, herbicides, and trace elements. Such materials include combined TMTD (50 percent TMTD and 12–20 percent lindane or 20 percent heptachlor), Phenthiuram (40 percent TMTD, 10 percent copper trichlorophenolate and 20 percent gamma isomer of hexachlorocyclohexane), mercurane (2 percent ethylmercuric chloride and 12 percent gamma isomer of hexachlorocyclohexane), and Mercurohexane (1 percent ethylmercuric chloride, 20 percent hexachlorobenzene, and 12 percent gamma isomer of hexachlorocyclohexane). Such systemic materials as Vitavaks (C₁₂H₁₃NO₂S) are used to suppress internal infection in seeds, for example, wheat and barley smut.

Some seed-treating materials, such as thiocyanogen, TMTD, and pentachloronitrobenzene, have immunizing properties as well as disinfectant ones. That is, they increase the resistance of such crops as cotton, cucumbers, and tomatoes to lodging, Fusarium wilt, Verticillium wilt, phytophthora, and clubroot of crucifers. When seeds are treated with materials that have an immunizing action, the plants’ resistance to disease is increased and maintained. All seed-treating materials produced in the USSR are in dust form, with the exception of formaldehyde and thiocyanogen.

In most cases, seed-treating materials decompose through the action of soil microflora or are absorbed by the soil. Seed-treating materials must be safe for seeds, toxic to agents of disease, chemically stable, capable of maintaining physical properties during storage, harmless to man and farm animals, and economical to use. Grain treated with organo-mercury compounds cannot be used for human food or livestock feed. In the USSR, dyes are added to such materials so that grain treated with them will have a distinctive color.

Seed-treating materials are also used to disinfect seedlings.