Trichoderma composite biological agent for preventing and treating fusarium wilt of watermelons planted on gravel-covered dry farmland, and application of trichoderma composite biological agent

The invention discloses a trichoderma composite biological agent for preventing and treating fusarium wilt of watermelons planted on gravel-covered dry farmland, and application of the trichoderma composite biological agent, and belongs to the field of biological prevention and treatment. The trichoderma biological agent comprises at least one of Trichoderma afroharzianum CGMCC No.22433, T. atroviride CGMCC No.22432 and T.longibrachiatum CGMCC No.22434. The trichoderma strain disclosed by the invention has a large spore yield, an obvious inhibition effect for the pathogenic bacteria of the soil-borne disease fusarium wilt and a stable character, is free from pollution and public nuisance, has a simple use method and a low price, is capable of forming a symbiotic relationship with a host in a plant body, is high in stability, is capable of improving the soil micro-ecological environment and has an obvious in plant growth promotion effect. After the trichoderma composite biological agent is applied, the use amo