What is Fusarium and How Does It Affect Cannabis Plants

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Added 30 August 2022

When growing cannabis, you will constantly battle against environmental factors, bacteria, fungi, etc. 

But there is one type of fungi that you need to be extra careful of to protect your plant.

The fungus is fusarium, which can wreak havoc in your garden if you don’t take the right measures. It starts slow, at the bottom of the plant, but quickly turns into a nearly unstoppable infestation — it will kill your plant, and its neighboring plants, and even ruin the soil.

So, what is fusarium and how does it affect cannabis plants? Learn all about fusarium and how you can protect your plant from it. 

What is Fusarium Fungi?

rotting stalk

Image credit - masterofsmeagol 

Fusarium is a type of fungi from the filamentous genus, which lives in the soil with various plants, including cannabis. Most of the fusarium species are classified as saprophytes, i.e., they feed on the organic debris within the soil.

But some types of fusarium can turn into parasites, preying on host plants. So, plants that play host to this fungi suffer from fusariosis. And when it gets out of hand, it can spell death for your entire garden.

Essentially, when fusarium mold infects a plant like cannabis, it can turn the roots ineffective. The mold exists in various strains, which can be classified by the mold color — white, red, green, pale yellow, and brown. 

It is dangerous for many plants to the point that it is recognized as a pathogen to crops across the world. 

Fusarium fungi are quite common and live in the soil dormant for years. But when the ideal conditions arise within the soil, it can quickly start multiplying and take over your crop, eventually destroying it. 

Humanity and Fusarium

According to experts, fusarium fungi are more common in plants that we, as humans, grow and consume. So, there is a theory that the problem of this fungi may be so common due to our agricultural and soil management practices.

For instance, according to a 2012 report by The Agricultural Biotechnology Council of Australia, a potential link exists between fusarium outbreaks and the use of certain herbicides. 

But fusarium fungi isn’t only dangerous for the plants we grow, it can even affect us. It is used as a contamination agent in various labs for a reason. For example, some species of fusarium produce mycotoxins when they attack cereals, which can cause diseases like fungal keratitis, Panama disease, and onychomycosis, along with various skin infections.

In fact, the Soviets have even been accused of using this fungus as a biological weapon in Afghanistan and Laos. So, you can see how dangerous this fungus can be for plants and even humans.

How Does Fusarium Attack Cannabis?

wilting leaves

Image credit - bronzeman 

During a fusarium infestation, the fungi take over the entire plant, leading to fusarium wilt. It starts by attaching itself to the roots and making them ineffective by stripping the plant of various vital nutrients, which leads to the plant growing feeble and wilting.

At the root zone, fusarium can also cause root rot, which further affects the plant’s health. 

Next, the fungus colonizes the xylem tissues, which blocks the crucial vessels within the plant that are responsible for transporting nutrients and water. This further damages the plant, causing the leaves to wilt and turn yellow. It can even lead to necrosis and eventually kill the plant.

While the infestation mostly occurs at the root zone, sometimes, it can even occur due to wounds on the plant due to contamination. Here, the fungus gets into the plant when you use contaminated pieces of equipment while training the plants. 

Some species of fusarium fungi can even lead to stem cancer in the plant. These species also prey on the plant like other Fusarium species — starting at the root zone and making their way up to the plant. 

Many types of fusarium fungi are dangerous to the cannabis plant, such as the following:

  • Fusarium fungi that attack the stem
    • Fusarium Sulphureum
    • Fusarium Lateritium
    • Fusarium Graminearum
    • Fusarium Avenaceum
    • Fusarium Sambucinum
    • Fusarium Culmorum 
  • Fusarium fungi that attack the roots
    • Fusarium Solani
  • Fusarium fungi that attack the veins 
    • Fusarium Oxysporum

These are just a few of the common species of fusarium that attacks cannabis, but there are hundreds more, along with various sub-species. But the two most common species you may encounter while growing cannabis is Fusarium Oxysporum and Fusarium Solani. 

What Causes Fusarium Infestation in Cannabis?

fusarium cannabis plants

Fusarium is a serious problem while growing cannabis, and it can occur due to several reasons. Perhaps this is one reason why it is difficult to protect your plant from this fungus. Here are some of the most common factors that can lead to fusarium infestation in cannabis.

Using Infested Seeds, Tools, or Soil 

The most common cause of fusarium in cannabis is using soil, tools, or seeds that are already contaminated with fusarium. You may not notice fusarium being a problem at first, because it can stay dormant for years, but if the ideal conditions are met, it can quickly grow and multiply. 

Improper Growing Conditions

As mentioned above, fusarium occurs when the right conditions are met — which may not be right for your cannabis plant. For instance, if the temperature ranges from 12°C to 28°C (53.6°F to 82°F) with high relative humidity, insufficient light, and soil with low pH and nitrogen levels and high potassium levels. 

In such cases, fusarium can prey on your cannabis plants quickly, whether it was dormant in the soil or brought to your garden from the air or contaminated tools. 

Fusarium is unlike other infestations because it can remain active in the soil for up to six years, thanks to its natural conservation mechanism. So, if your plant is infected by fusarium once, it will mostly occur in plants around them or after them, if you use the same soil or tools. 

What are the Symptoms of Fusarium in Cannabis?

fusarium on cannabis

Fusarium, in its dormancy, is difficult to catch, but once it starts its full-fledged attack on your plant, it is easy to spot. But it may be too late by then. 

The first signs of fusarium occur in the leaves — they begin to turn yellow, droop, and die off. Another early sign of fusarium is root rot, where the roots turn red and slimy. 

Soon enough, the slime and redness from the root start to travel up. This is a sure sign that your plant is suffering from fusarium infestation. Other symptoms you can look out for are:

  • Wilting of leaves
  • Leaves turning yellow, especially the lower ones
  • Brown spots on the leaves 
  • Leaves curling up
  • Red stem and roots
  • Swollen stem 
  • Punctured stem
  • Necrosis of the stem 
  • Lignification at the lower stem
  • Signs of nutrient deficiencies in the leaves and branches 
  • If you were to cut the stem, you would see brown vascular bundles 

In most cases, these symptoms will first appear at the base of the plant and move upwards. 

How to Prevent and Control Fusarium in Cannabis?

root rot

Unlike other forms of infestation, fusarium is difficult to combat. In many cases, it is impossible to save your plant. So, your best option is to prevent fusarium in the first place if you want to protect your plant. Follow these techniques to prevent fusarium from growing in your garden.

Ensure Your Soil is Getting Enough Oxygen

Not all bacteria and fungi are bad if they grow in the soil. Some of them help create nutrients at the root zone and even protect the plant from other diseases. So, you need to cultivate the right conditions to invite helpful fungi into the substrate, which will prevent fusarium from taking over. 

The most effective way of inviting beneficial fungi into your substrate is to ensure it gets adequate oxygen at all times. 

Use Fans in Your Garden

Like any other fungus, fusarium grows best in heat and moisture. So, an effective way of slowing down its growth is by using fans in your garden to keep the temperature and moisture levels in check. 

This especially applies in an indoor growth setup, where the soil tends to heat up due to the powerful grow lights. 

Your goal should be to create a cross breeze in your garden with the help of fans and vents, which ensure a fresh airflow at all times. 

You should also consider investing in a hygrometer to track your grow room’s humidity levels. When you first germinate the seeds, you can set the humidity to 70%, gradually decreasing by 5% every week until you reach 40%. 

Maintain Utmost Levels of Hygiene

Many growers use their tools and stash them in their garages. This is not healthy for the plants. You need to be strict with hygiene whenever you are growing a plant.

You need to disinfect tools like trimmers, pots, irrigation tanks, etc. before use. You should also disinfect your grow room regularly, including the floor, windows, walls, and ceiling. And do not overlook other things like trays, vents, and light panels, either. While they may not come in direct contact with the plant, they can still host spores that can travel to the plant. 

You also need to maintain hygiene at a personal level. So, never wear the same clothes you wear outdoors. Instead, keep a specific set of clothes that you only wear while working in your grow room. This prevents the spores from hitching a ride on your shoulders. 

But how do you maintain hygiene in an outdoor garden? That’s a valid question — maintaining hygiene and disinfecting an outdoor garden is difficult. In such cases, you can start by keeping an eye on the surrounding plants for any signs of fusarium fungus. You should also get rid of any weeds in your garden and other plant debris like old leaves or branches. 

To keep the soil medium clean, you can use soil solarization. Here, you have to cover the substrate with a see-through plastic sheet, which will reduce the chances of fusarium infestation drastically. 

Use High-Quality Substrates

You need to ensure that the substrate — especially soil — you use to grow cannabis is of high quality. You should also be aware of its properties. This is why it is crucial to buy high-quality soil from reputable retailers or manufacturers. 

Avoid buying soil where you don’t know what kind of soil it is, and the same applies to other types of substrates. A reputable manufacturer will mention all of its properties on the package so you know exactly what to expect.

Ideally, you should never choose anything low-quality — soil, fertilizers, nutrients, seeds, etc. — the quality of the products and materials used during growing cannabis partly dictate the quality of your yield. 

Encourage a Rich Ecosystem in the Soil

If you are growing cannabis in soil, you need to ensure the substrate is a rich ecosystem. As mentioned above, you need to invite beneficial fungi to dominate the soil, so the fusarium does not grow there.

Along with that, you need to maintain a fine balance in the soil concerning bacteria, nutrients, organic matter, etc. You can do so in various ways, like using compost tea or adding bacterial food like diluted molasses in the soil.

Organic soil is an ideal option for growing cannabis outdoors because it can ward off fusarium thanks to nature’s checks and balances. And experts agree. According to a 2014 study published in Applied Soil Ecology, organic soil was better at warding fusarium when compared to non-organic, conventional soil.

Add Trichoderma to the Soil

Trichoderma is a beneficial fungus that can encourage explosive root growth. But it can also help prevent fusarium. Trichoderma is a colonizing fungus that quickly overtakes the soil, keeping other species of fungus from growing within. 

Ensure Good Soil Drainage

One of the major reasons why excess moisture may exist in the substrate is poor drainage — a mistake many new growers commit. And moisture is an excellent way to invite fusarium into your garden, along with various other fungus species. 

So, if you want to avoid fusarium infestation in your garden, you need to ensure that your soil drains water well. 

The solution is simple — only water your plants when the top inch of the soil is dry. And if you use pots, ensure at least 20% of the water drains from the bottom of the pot as soon as you water the plant. 

Maintain Soil pH Levels

Fusarium enjoys slightly acidic conditions, so ensure the pH levels do not stray too far from what’s healthy for the cannabis plant. If you are worried about fusarium in your garden, maintain the pH level slightly above six, but do not exceed 6.5. 

The slightly higher pH level will not only prevent fungus but also encourage good bacterial growth in the substrate, which will only improve the soil conditions. 

Rotate Your Crops

When growing cannabis outdoors, it is a good idea to not grow plants in the same place season after season. This is because fusarium can stay stagnant in soil for years. You should avoid creating a cannabis monoculture in your garden.

So, it is recommended that you rotate your crop.

Grow Cannabis in a Permaculture Guild

Alternatively, you can also protect your plant from the fungus using a permaculture guild. In a permaculture guild, you plant multiple plants, not just cannabis. The other plants act as companion plants that help the cannabis plant grow well by either fixing nutrients in the soil, acting as a decoy for pests, or even stopping spores from being spread around in the garden.

Check Your Plants Regularly

Whether you're growing cannabis indoors or outdoors, you should keep a close eye on your cannabis plant. Look out for the signs of excess moisture, root rot, fungus, etc., along with the various symptoms that are specific to fusarium fungi. 

If you notice any signs of fusarium, you need to act quickly. Learn how to treat fusarium infestation in the following section.

How to Treat Fusarium Infestation in Cannabis?

browning leaves

Fusarium fungi in cannabis are difficult to treat, but with the right techniques, you can still get rid of them. Here are a few methods you can consider using.

Remove the Infected Plants ASAP

Once you notice fusarium infestation on your plant, you need to act quickly by removing any infected parts from the plant. Whether it is a small mold patch on the leaves or an entire branch covered in fungus — cut it off and sterilize the tools immediately.

Don’t hesitate to Toss the Plant

If the infested plant is growing close to other plants, whether cannabis or others, you should toss the plant and not hesitate at all. It is better to lose one plant than to lose your entire culture. 

Fusarium can quickly turn from a small mold spot on a leaf to covering all the plants in fungus.

Follow removing the infected parts or plants by treating the soil with Trichoderma — this will discourage fusarium growth in the substrate. 

Maybe Get Rid of the Soil Entirely

If the infestation is severe, you should consider getting rid of the soil too. Avoid turning it into compost, either — the fungus will live on and damage the future plants treated with that compost. 

Instead, you should dump it in a yard waste container, or let it bleach and dry out. You can even cook the soil by covering it with a sheet of black plastic under the sun to kill off the fusarium. 

Switch Growing Locations

If you are growing plants in your garden (not in a pot), getting rid of the soil may be difficult. You should switch the growing location and move to a different part of your garden. 

Use Hydrogen Peroxide

You can also try treating the soil with hydrogen peroxide, which reacts with molecules in the soil, including fusarium. But remember that it can be toxic for your plant (and other organisms) in high concentrations. So, you should always dilute the solution before treating your soil with it. 

Remember, there is no guarantee that these methods will help you get rid of fusarium fungi. It is a nasty fungus that can destroy your crop. So, you should still stick to avoiding it at all costs using smart growing tactics. 

Summary: Fusarium and Cannabis Plants

You should never underestimate fusarium and how it can affect your plant. In the US, from 1991 to 1996, fusarium solely was responsible for damages worth USD 300,000 million in the wheat and barley industry.

Remember the following tips to keep fusarium away at all costs:

  • Always clean and disinfect all the tools and equipment before use
  • Clean and disinfect your grow room regularly 
  • Use an airy substrate with enough oxygenation and drainage to avoid moisture buildup
  • Never soak the substrate — only water the plant when the soil’s top inch is dry
  • Use fans and vents to keep airflow and temperature in check 
  • Keep your substrate’s temperatures under 25°C
  • Use beneficial fungi and bacteria in the substrate to keep fusarium away
  • Use clean clothes and gloves when going into your garden and do not wear clothes that you have worn outside
  • Avoid reusing the soil. Instead, try rotating the plant 
  • If you are growing cannabis outdoors, use soil solarization 
  • Do not overfeed your plant, especially with nitrogen and potassium
  • Keep the pH levels around 6 to 6.3
  • Always buy seeds and soil from a reputable, high-quality supplier
  • If you bring in clones, quarantine them for the first couple of weeks and look out for any signs of fusarium
  • Treat your substrate with Trichoderma regularly

Follow these tips and take care of your plant, and you won’t have to worry about fusarium attacking your cannabis plant. Fusarium is deadly for plants, so it is best avoided.

And if your plant experiences fusarium infestation, your best bet is to cut your losses, toss the plant, and get rid of the soil.

Fusarium is common, but if you take care of your plant, it won’t be a problem. 



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