Fusarium

[Medical Marijuana]

This disease is caused by a form of the same fungus that frequently causes damping-off; thus, many aspects of the life history are similar. For example, the pathogen overwinters as chlamydospores in small pieces of roots or organic matter, and when seedling roots grow near these spores, germination occurs and the pathogen enters the roots. However, development is delayed until later in the growing season, when larger and more crowded seedlings are stressed for moisture and nutrients. The fungus then grows rapidly throughout the root system and destroys it. Warm soil favors disease development. The sources of inoculum on container-grown seedlings is unclear; however, Fusarium can be seed-borne or infection may result from wind-borne spores.

Disease losses can be reduced in container nurseries that have a well-drained and aerated growing medium and that use irrigation regimes for preventing stress. Used containers should be thoroughly cleaned (according to current recommendations) because Fusarium can occur on them. In bareroot nurseries, heavy soils favor the pathogen, supposedly because of the slower decomposition rate of the pathogen's food bases (e.g., root pieces). The disease can be effectively prevented by locating bareroot nurseries on lighter soils.