Residual Fungus

• Once a fungal disease is present in the soil, it often remains for as long as it continues to have enough energy to sustain itself. Some stay in soil for a very long time but stay dormant until there is a target worth attacking. For example, the Phytohthora fungus lives in the soil until it has prey worth latching on to. Crop rotation that includes plants susceptible to different types of fungus helps ensure that a given soil fungus can't get a strong hold.
  
  

Drainage

• Water is one of the essential ingredients for the growth of most fungi. The more water sits in a particular area, the more it encourages the growth of any fungus that might be in the soil. Soil with excellent drainage helps to eliminate fungal growth. Well-drained soil allows water to pass by the plant roots so the plant gets the moisture it needs without the water staying long enough to encourage a fungus.
  
  

Pathogens

• Not all fungi that live in soil are harmful. Of the three primary types of fungus that live in soil, only one creates disease that affects plants. These are the pathogens or parasitic fungi. Verticillium and Rhizoctonia are examples of the types of fungus that live in soil and attack plants. However, other fungi in the soil play vital roles in helping decompose soil and helping transmit important nutrients to plants.
  
  

Fungicides

• Fungicides attack and kill fungi in the soil. Fungicides are manufactured to use a number of different mechanisms to combat fungus. Some directly attack and kill the fungus, but others work in more subtle but still effective ways. An effective type of fungicide against soil fungus is called a direct-competition fungus. This introduces an organism to the rhizosphere that competes with the bad fungus, leaving it unable to grow and attack the plants in the area. This type of fungicide needs to be applied before plants have been affected by a soil-borne fungus to be effective. It prevents infection rather than curing it.