Fusarium in Cannabis

Fusarium is one of the most common fungal diseases affecting hemp and can lead to crop failure or even the death of entire plants. Fungi of this genus are widespread in many cultivated crops around the world and are also found on food. They are considered among the most dangerous pathogens for the cannabis plant [1].

In 1970, a scientist from the University of California proposed to then-President Nixon that Fusarium wilt could potentially destroy illegal marijuana cultivation worldwide [2]. The Nixon administration subsequently funded research aimed at mass-producing the wilt-causing fungus. The project was later discontinued by officials under the Carter administration.

 

How can you recognize a Fusarium infection?

The most important species that cause damage to cannabis are Fusarium oxysporum and Fusarium solani. Both species cause different symptoms in cannabis [3]:

 

    • F. oxysporum causes what is known as Fusarium wilt.
    • F. solani causes root rot.

 

While root rot is usually localized to the roots and the stem base, Fusarium wilt is systemic, meaning it spreads throughout the entire plant. Both species can also cause the embryo in seeds to die before germination. By clogging the xylem vessels, they block water transport and cause the plant to wilt.


Disease Progression of Fusarium Wilt:

 

  1. The symptoms of Fusarium wilt begin as small, dark, irregular spots on the lower leaves.
  2. Affected leaves suddenly become chlorotic (yellow).
  3. The leaf tips curl upwards.
  4. Wilted leaves dry to a yellow-brown color and remain attached to the plant without falling off.
  5. Petioles, branches, and sometimes even the stem can become limp. The plant may topple over.
  6. The stems also turn yellow-brown. When cutting into wilted stems, a reddish-brown discoloration of the xylem tissue is visible.

Fusarium Welke, Fusarium bei Cannabis, Fusarium oxysporum, Fusarien Infektion Cannabis, Fusarien Infektion Hanf

Image source: JM McPartland (2004) [3]

 

Disease progression of root rot:

 

  1. Penetration of spores through injuries in the root tips
  2. Roots discolor from white to brown.
  3. Roots become mushy/slimy and easily detach.
  4. Plants show the first signs of water deficiency, even though the substrate is moist.
  5. The plant takes up very little water, and the leaves and stems turn yellow and partially dry out.

Fusarium root rot, Fusarium solani in cannabis, fusarium test cannabis, Cannabis Wurzelfäule

Image source: SH Wang (2021) [4]

How to successfully combat Fusarium?

Currently, there is no cure for plants infected with Fusarium. Therefore, it is crucial to take measures to prevent an infection from the outset.

 

    • Avoid overwatering.
    • Ensure good drainage in the substrate.
    • Thoroughly clean cutting tools with alcohol, Purolyt, or hydrogen peroxide.
    • Use sterile substrates. Fusarium is considered a soil-borne disease.
    • Test seeds and use pathogen-free seeds. Fusarium fungi can be transmitted through seeds [5][6].
    • Provide sufficient nitrogen according to the plant’s needs, but avoid excessive fertilization with this nutrient and prefer nitrate forms over ammonium forms.
    • Root-strengthening beneficial organisms such as Trichoderma (e.g., in Rootshield Plus) and Bacillus subtilis [7].
    • Remove infected plants and their substrate.

 

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References

  1. Gwinn KD, Hansen Z, Kelly H and Ownley BH (2022) “Diseases of Cannabis sativa Caused by Diverse Fusarium Species.” Front. Agron. 3:796062. doi: 10.3389/fagro.2021.796062
  2. Shay R., 1975. Easy-gro fungus kills pot among us. The Daily Californian, March 14, pg. 3
  3. John M. McPartland & Karl W. Hillig (2004) “CANNABIS CLINIC Fusarium Wilt.” Journal of Industrial Hemp, 9:2, 67-77, DOI: 10.1300/J237v09n02_07
  4. Shouhua Wang (2021) “Diagnosing Hemp and Cannabis Crop Diseases”. CABI Digital Library pp. 197-223, https://doi.org/10.1079/9781789246070.0009
  5. https://pnwhandbooks.org/plantdisease/host-disease/hemp-cannabis-sativa-fusarium-wilt
  6. Gwinn KD, Hansen Z, Kelly H and Ownley BH (2022) “Diseases of Cannabis sativa Caused by Diverse Fusarium Species.” Front. Agron. 3:796062. doi: 10.3389/fagro.2021.796062
  7. Cameron Scott & Zamir K. Punja (2023) “Biological control of Fusarium
    oxysporum causing damping-off and Pythium myriotylum causing root and crown rot on
    cannabis (Cannabis sativa L.) plants”, Canadian Journal of Plant Pathology, 45:3, 238-252, DOI:
    10.1080/07060661.2023.2172082

 

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