Seedsman Blog


We continue our series on problematic pathogens with a look at perhaps the deadliest of them all – the dreaded Fusarium (Fusarium Oxysporum, Fusarium Vasinfectum)

What is it?

Fusarium is arguably a grower’s worst nightmare, and another of our fungal foes, but with the ability to take down entire crops at record speed. Lurking just below the surface of the soil, this botanic bully has a rap sheet to be feared. Devastating to a range of crops including wheat, coffee, cotton, and tomatoes, this pathogen is so powerful that some Governments actually weaponised Fusarium, spraying entire cannabis farms from the skies as part of the war on drugs.

What does it look like?

Fusarium symptoms present as similar to other conditions, but plants typically show signs of weakness and nutrient deficiency. Be on the lookout for the following:

  • Dark spots on the lower leaves
  • Yellowing/browning of leaves, followed by wilting
  • Upward curling of leaf tips
  • Signs of decay at the roots or on stems
  • Slow or stunted growth
  • Red, reddening, or reddish-brown roots just below the topsoil (aka Root Rot)
  • Fungal growth on the outside of stems which appears orange, pinkish or white

What does it do?

Fusarium attacks plants at the root and leaf level, consuming nutrients, starving the plant, and quickly destroying it from the ground up. Discoloration of the leaves can progress to splitting stems as the plant starves, wilts, and collapses.

What can I do to treat it?

In short, nothing. It’s that bad. Employ all the usual preventative measures we apply to other pathogens – temperature and humidity control, airflow, and good hygiene practices. These can at least reduce your chances of infection. There are conflicting opinions on the prevention and treatment of Fusarium, with some studies suggesting that, as Fusarium is known as a soil-dwelling pathogen, utilising a hydroponics set up is the way to go. Other studies, however, suggest that hydroponics setups in Canada have been blighted by Fusarium in the past. As Fusarium easily spreads through soil, water and air, there is no known method of growing cannabis which can ensure any kind of immunity to this evil pathogen. The conflicting opinions of studies only serves to muddy the waters when looking to take both proactive and reactive steps to Fusarium. Monitoring pH levels and soil treatments are among other recommended methods of keeping risk under control, but soil-based crops can be set up to limit the spread of Fusarium.

  • Container Gardening  – Where each plant is potted individually. This method will ensure that, should one pot fall prey to Fusarium, that pot can be quickly removed, and the plant destroyed without the pathogen spreading through the soil to other plants, putting the entire crop in jeopardy. Use sterilised or pasteurised soil, and sterilised (or new) pots.
  • Ensure soil pH doesn’t get too low. Test regularly, and neutralise acidic soil with dolomite lime or greensand.
  • Consider the addition of beneficial bacteria (Mycorrhizae) to help improve disease resistance. These are available in seed treatment form (Bacillus), or soil drenching form (Azotobacter) and can affordably, effectively, and organically offer a decreased risk of infections.
  • Be aware that if a crop succumbs to Fusarium, that ground can no longer be used to grow Cannabis. Additionally, seeds produced by infected plants must not be used, as the pathogen lies dormant on the seed until the seedling emerges, when it then attacks the plant.

Unfortunately, once infected, the only truly effective means of control is to remove and destroy all infected plants. After removal, ensure all tools involved in the removal process are cleaned thoroughly with Hydrogen Peroxide before using them again, lest ye run the risk of inadvertently spreading the pathogen to your healthy plants. Always keep your hygiene game strong.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

This post is also available in: French

Duncan Mathers