Different fungal biopesticides can be used to control plant diseases (caused by other fungi, bacteria or nematodes), as well as some insect pests and weeds. Fungi are a diverse group of organisms and can be found in almost every environment on Earth. Most have complex lifecycles, and some are parasitic to various eukaryotes, including plants and insects.  Some species have proven useful as microbial biopesticides. However, because they are living organisms, they do require specific environmental conditions to proliferate. 

Because fungal biopesticides are so diverse in nature, their means of affecting the target pest can be equally diverse. The most common modes of action are through competitive exclusion, mycoparasitism, and production of metabolites. Some fungi can exhibit all of these modes of action. Two of the most common commercial fungal biopesticides are Trichoderma spp. and Beauveria bassiana. Each are frequently used in the nursery, ornamental, vegetable, field crop, and forestry industries to control a variety of pests.

Trichoderma spp. are some of the most common fungi in nature. Many beneficial Trichoderma have the ability to readily colonize plant roots, without harming the plant. It is this close relationship with the plant that make these species excellent biocontrol agents. These microbial biofungicides can out-compete pathogenic fungi for food and space, and in the process can stimulate plant host defenses and affect root growth. In addition, they have the ability to attack and parasitize plant pathogens under certain environmental conditions.

Beauveria bassiana is a fungus that acts as a parasite on many insect species. B. bassiana has a broad host range, although individual strains may be restricted in the number of insects it can attack. B. bassiana spores adhere directly to the host cuticle, where they will germinate, produce enzymes that attack and dissolve the cuticle, penetrate, and grow into the insect’s body, feeding on internal tissues and releasing an insect toxin. As the insect dies, it changes color to pink or brown and eventually the entire body cavity is filled with fungal mass. B. bassiana has proved  effective in controlling troublesome crop pests such as aphids, thrips and whitefly – even chemical pesticide-resistant strains such as Q-Biotype Whitefly.