When humans are out in the forest picking mushrooms, they have to be aware that some species are highly medicinal and others are incredibly poisonous. This same relationship within fungi also applies when cultivating cannabis plants. Some fungi form a symbiotic relationship with plants that helps with the uptake of nutrients from the soil. However, some species are not so friendly and can in fact be lethal to an entire cannabis crop. Fusarium is a large genus of fungi that fits the latter description. This fungus can wreak absolute havoc on cannabis plants and cannot be treated once detected. This makes prevention of the utmost importance.

Fusarium can lay dormant within the soil for years at a time before it becomes active and starts to detrimentally affect crops. This makes the fungus incredibly hard to detect, meaning many of your plants could be vulnerable to an attack without any warning signs.

Fusarium has a tendency to attack crops that humans typically cultivate; this could be due to the choice of chemicals and pesticides that many cultivators choose to employ. The fungus is usually spread by running water, garden equipment and other tools. The dormant cells spring into action when they detect a suitable host plant, with cannabis being an ideal target on their radar.

fusarium fungus cannabis soil roots


The two main symptoms of fusarium are wilting and root rot, with each of these signs being caused by different subgenera.

Some of the first signs of the wilting damage caused by a fusarium attack will manifest in leaves quickly turning to shades of yellow and brown. These suffering leaves will also display tips that curl upwards. Leaves will lose vigour and look as though they may drop off, although it is unlikely that they actually will. These symptoms are sure signs of fusarium wilt.

If your plants have unfortunately fallen victim to fusarium root rot, you may very well detect multiple symptoms. One obvious sign is that the roots of your crop will start to display a reddish complexion. Because the roots are almost entirely covered in soil, it won’t be evident that your plants have the condition until this colour starts to move up the stems of plants. The rotting will continue to climb the stalk, splitting it along the way, eventually culminating in infestation and collapse.

This notorious fungus devastates plants from the inside out. It works to block vessels within plants that are used to supply water and nutrients. Without access to these fundamental building blocks of life, plants face a fast and imminent death.

fusarium root rot leaves fungus cannabis


If your plants have been attacked by fusarium, it is evident that the soil at that particular grow site is infected with the fungus. In the case of infestation, it would be wise to start a new grow as soon as possible in a location far away from this site. If you are growing indoors and your crop was infected, clean the grow space and replant another crop in different soil. If your crop does show signs of a fusarium invasion, it’s time to put it to rest and start again. It has been reported that smoking plant matter infected with fusarium can make a person sick, especially if they have a compromised immune system. Prevention is key here.

One ideal option for preventing fusarium is to cultivate plants within the controlled environment of a grow tent. This setup allows growers to have almost complete control over factors such as temperature, moisture and air flow. Some types of fusarium grow in anaerobic conditions, meaning without oxygen. Although some types grow in aerobic conditions, with oxygen, ensuring good air flow will minimise exposure to the species that cannot tolerate air.


Fusarium has an affinity for the conditions of heat and moisture. Unfortunately, many grow room setups harbour this exact environment, using lots of water and very hot lights. Growers can pay strict attention to humidity levels by using a device called a hygrometer. Dehumidifiers can then be used to bring humidity down as plants require less over time.

As far as moisture goes, be sure to water your plants in the correct fashion. It is extremely common for novices to overwater their plants as a precaution for underwatering. However, too much water creates the ideal battleground for a fungal attack and also minimises the presence of oxygen. Make sure that the top inch of soil is dry before watering your plants again in order to prevent these conditions.

fusarium fungus rotten cannabis bud


Hydrogen peroxide can be applied to soil to disinfect the substrate, as well as oxygenate it. About 20cc of hydrogen peroxide per litre of water is reported to achieve these desired effects.

Before even planting crops, some growers may opt to use natural fungicides in an attempt to eliminate the risk of fusarium. These include preparations of nettle and horsetail. Adding compost tea or bacterial food like molasses can help to support healthy bacteria and fungi within the soil. Using a clay soil will also help to prevent cases of fusarium due to the higher pH levels of this substrate.

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