Trichoderma fungi are found naturally occurring in many soils and play an important role in the prevention and control of root pathogens. It actively takes over the root zone and makes it difficult for pathogens to compete for space on the roots and for nutrients.
Trichoderma is not just one species of fungi – the genus Trichoderma contains many species and strains, of which some are specific to certain pathogenic fungi such as Pythium. Of all the Trichoderma species, T. harzianum, of which there are several strains, is the most widely commercialized and has been found in scientific studies to be effective against a wide range of fungal plant pathogens.
Trichoderma fungi produce powerful enzymes that can dissolve crop residues and attack soil pathogens. There are two main types of enzymes that trichoderma produce: cellulase and chitinase. Cellulose, a major component in plant fibers and crop residues, can be broken down by the enzyme cellulase. Chitin is a structural component in fungal cell walls and a key component in insect exoskeletons, which can be broken down by the the enzyme chitinase.
Trichoderma switches back and forth on which enzymes to produce depending on the type of food source available. This means that in the springtime, when temperatures are low and pathogen activity is low, trichoderma will feed on the readily available cellulose from crop residues. Later in the season when the crop residues are exhausted and the pathogen load has increased trichoderma will switch over to parasitizing the pathogens.
There is another kind of beneficial fungi that is commercially available to growers and also covers the roots to physically prevent disease infection and make nutrients available to the roots — mycorrhizal fungi. People often confuse the two fungi but mycorrhizal fungi are not parasitic like trichoderma fungi. Both of them combined will promote a very healthy root system overall. The two work together well.