Trichoderma harzianum:

Trichoderma harzianum is a common fungus that can either saprotrophic in free soil and dead wood or biotrophic in necrotrophic mycoparasisitic attacks of other fungi and endophytic associations with plants. Trichoderma harzianum colonizes plant roots and normally will attack and parasitize other fungi to gain nutrition.

It is its mycoparasitic ability that makes Trichoderma harzianum very useful. It is being used as a bio control agent in many commercial bio-fungicides. It is predominantly used either as a foliar application or for soil treatment, for the suppression of certain fungal pathogens.

Allegedly, it is also very useful for the treatment of Botrytis and Fusarium (Roots Rot) and some orchid growers claim that it also helps with Rhizoctonia and Phythium. Of course, healthy roots = healthy plants.

It is commercially produced under various names. Check your local store and follow the written directions.