How to Prevent Verticillium Wilt When Growing Cannabis

A growing cannabis plant is constantly fighting with various forces of nature during each of its growth stages. It fights bacteria, fungi, pathogens, pests, and so much more. But sometimes, your cannabis plant is unfortunate enough to come across verticillium, a harmful fungus that can completely ruin and kill your plant. 

So, what is verticillium, what's its life cycle life, and what you should do if your cannabis plant suffers from verticillium wilt — if these are the questions that pop into your mind or you are already looking for a solution to verticillium wilt, look no further. In this article, we tell you everything you need to know about verticillium wilt. 

Verticillium is caused by many verticillium species, but the most common species include verticillium albo-atrum and verticillium dahliae. There are many different species of this fungi and they all differ from each other, but we will focus on the two most common species of verticillium in this article. All in all, the differences don't matter much when it comes to preventing or dealing with verticillium in your cannabis garden. 

What is Verticillium? 

Verticillium is a type of fungi that belongs to the Deuteromycetes class, which is also known as fungi imperfecti. This fungus spreads via spores that later get activated in the soil. 

In the soil, these fungi spores can live for years and wait for the right host to come by. Once they find a good host, i.e. your cannabis plant, they enter the plant via the roots. This is why it's crucial to sterilize the soil between every harvest. 

Once the fungi enter the body of the plant, they attack the xylem within, which is responsible for water transportation. When infected by this fungi, the xylem degrades and eventually dies, which leads to the eventual death of the host plant, too, since they distrust the water cycle in the plant. The plant essentially dies of dehydration. 

Verticillium affects many plants like potato, peppermint, maple, and cannabis. 

Life Cycle of Verticillium 

You can call verticillium a very opportunistic nuisance. This fungi lives in the soil in saprophyte form, and during the winter months, they turn to microsclerotia, which is a condensed mass of mycelium. This mass is propagule in nature, collectively with other fungi species. 

Once the fungi find a host, the infection begins. This problem starts at the root level, where the verticillium hyphae germinate (when the environmental conditions are right) and start penetrating the plant's roots. 

Sometimes, these fungi can enter the roots via small wounds too. Within the roots, the infection starts spreading thanks to mycelium or microcode spores. Over time, they travel to the xylem of the plant, where the spores make themselves at home. 

Once the spores have lodged within the xylem, the hyphae start multiplying quickly. The infection grows and spreads, and the mycelium and its by-products start clogging the xylem, eventually turning the infected parts necrotic or dead. Once the xylem gets clogged, the plant can no longer transport water sufficiently from the roots to the stems, and the plant starts showing signs of drought, including wilting. 

Where Does The Verticillium Fungi Originate?

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As mentioned earlier, verticillium is activated in the soil, making it a soil-based pathogen. So, if you plant a cannabis seed in verticillium-infected soil, it will likely be infected by this fungi. 

However, soil isn't the only way this fungi can spread to your cannabis plant. Verticillium can also spread via the organisms living in the soil, water, weeds that act as hosts, infected plant matter, and contaminated or infected gardening tools. 

This begs the question about this fungi's contagiousness. Yes, verticillium is highly contagious. It can travel to your cannabis plant via many vectors, including gardening tools, bad soil, water, your clothes, air, pests, and much more. 

Thus, it is crucial to maintain good hygiene in your cannabis garden and keep the tools and equipment sanitized at all times to prevent verticillium. More on this later. 

How to Identify Verticillium in Cannabis Plants?

Verticillium infection is known as verticillium wilt because it causes the cannabis plant to start wilting, which leads to chlorosis and ultimately necrosis. Identifying this fungal infection with just this symptom may appear challenging at first because wilting leaves are a sign of various diseases, but that's not the case. 

Verticillium wilt's primary symptom is wilting of the leaves but it exhibits itself in a few other ways (symptoms). So, if you suspect your cannabis plant is suffering from verticillium wilt, look for the following signs and symptoms. 

1. Wilting Leaves

As mentioned earlier, verticillium wilt primary symptom is wilting of the leaves. Once the plant gets infected by this fungus, it starts experiencing drought, which makes the leaves wilt. This symptom can sometimes occur with discoloration of the leaves. 

It is important to note that this wilting is not necessarily seen on the leaves. Depending on various factors like the infection severity and strain, the wilting may also appear in other parts of the plant like the branches. So, while you should ideally look for wilting leaves, don't be surprised if your plant's branches also appear wilted. 

2. Leaf Turning Brown or Yellow 

Another major symptom of verticillium wilt is the leaves turning yellow or brown. This is a result of chlorosis when the plant fails to develop chlorophyll due to a lack of water. This can obviously happen due to other conditions, too, but when the plant is suffering from verticillium wilt, the discoloration will begin between the veins and the edges until the entire leaf turns brown or grayish in color. 

During this time, another way to verify if your plant is indeed suffering from verticillium wilt is to look at the base of the stem. The stem's base may also start turning brown or yellow. So, if your plant's leaves appear to be wilted and discolored, look at the base of the stem, just above the soil line. 

3. Withering Leaves

If this condition is not addressed on time, the wilted and discolored leaves will completely die and wither off the plant. But dropping leaves can also be a sign of other plants. So, if you think your cannabis plant is suffering from verticillium wilt, look for the peculiar discoloration described above. 

If your plant's leaves have turned crispy and yellow and start dropping, it can be a sign of underwatering, too. Again, it is important to consider this symptom as a complement to others, not on its own. 

4. Discoloration of the Vascular Organs 

As verticillium fungi start flourishing in the xylem, necrosis begins at the infected site. So, another common symptom of verticillium wilt is that the vascular veins will start getting discolored — they will get darker. If you notice this symptom along with wilting, you can be almost sure that your cannabis plant is suffering from verticillium wilt. 

5. Slowed Plant Growth 

Once the verticillium fungi start growing in the xylem, the cannabis plant will fail to transport water and other essential nutrients from the roots to the stems. Due to this, our plant will also experience nutrient deficiencies of many kinds, which can hamper its growth. 

Do note that while stunted growth is a sign of verticillium wilt, it is advisable to only consider it as a symptom of this fungal infection if it's present with other symptoms listed above. On its own, stunted plant growth can signify many problems. This symptom will usually follow wilting and discoloring leaves, so you may not always spot it at the right time.

How to Treat Verticillium Wilt in Cannabis Plants?

In many cannabis problems, you can treat the plant right away and start noticing improvement within a week, but that's not the case with fungal infections. Often, fungal infections can't be treated, and the same goes for verticillium wilt. There is no treatment. 

However, what you can do is amend the soil before you start growing cannabis to bring down the chances of verticillium wilt. Remember, verticillium wilt thrives in soil that is packed with nutrients and lacks proper drainage. Here are some ways to treat verticillium in the soil.

1. Compost

One of the best ways to deal with verticillium in the soil is to use solarized compost. Experts aren't yet sure if compost can work efficiently if it is added to soil that is already heavily infected with verticillium, but compost definitely works to stop the growth of verticillium if the infection is still in its infancy. 

2. Mycorrhizal Fungi 

Mycorrhizal fungi are those that develop a symbiotic relationship with the roots of the plants, including cannabis. They are usually used by growers to improve their plant's growth as they help the plant improve its nutrient uptake, antioxidant metabolism, and secondary metabolite production. 

Plus, they can assist your cannabis plants against verticillium fungus. So, consider using this fungus if you suspect your soil is infected with verticillium.

3. Trichoderma

Studies suggest that one of the effective ways of stopping the growth of verticillium dahliae mycelium in the soil is using Trichoderma spp. Experts don't know how exactly trichoderma works in eliminating verticillium as the studies are lab-conducted and more conclusive results are still pending. 

Based on the initial studies, you can try using Trichoderma in your soil as it may help defend your soil against this fungus. Remember, it is not a sure-shot solution, but you can try it to see if it works for you.

Studies have shown that soil that's amended with compost and mycorrhizal fungi is at a much lower risk of verticillium. Yes, these tactics aren't true cures for the verticillium wilt, but it is the best you've got. 

Verticillium is a notorious fungus that ruins your cannabis plant. So, once your cannabis plant is infected with this fungus, the best thing you can do is cut your losses, harvest whatever you can from the infected plant, and start treating the soil. Even if you add the best compost to the soil, it won't improve the condition. You need to treat the soil instead. 

How to Prevent Verticillium in Cannabis Plants?

As mentioned earlier, there is no cure for verticillium, so it's best to prevent this fungus at all costs instead of trying to treat it. With most cannabis diseases, prevention is better than cure, but here, prevention is the only route you can take to safeguard your cannabis from verticillium. Here is how you can prevent verticillium in your cannabis.

1. Solarize the Soil Before Planting 

Sunlight is rich in UV light which is an excellent deterrent for many harmful spores, making it excellent for sterilizing the soil. So, it is recommended that you solarize your soil (and even compost) by exposing your soil to sunlight. Do this even before you plant your seeds so that your soil is sanitized and the plant gets a healthy rhizosphere. 

If solarization is not possible for your cannabis soil, you can also use pasteurization. In this process, you need to heat the soil in water at 80°C or 176°F for at least half an hour to kill off all the fungal spores and other pathogens within the soil. Post-pasteurization, the soil is sterilized much better than solarization, but this can be a cumbersome (and expensive) process. 

While solarization is an excellent way to kill off any verticillium spores in the soil, the process may also affect other beneficial life in the soil. So, you may have to re-treat your soil with beneficial life after solarization. 

2. Maintain Sanitation 

You must take a two-pronged approach to preventing verticillium growth in your cannabis garden. First is to prevent it entirely — which you can do by maintaining the utmost levels of hygiene and sanitation in your garden. So, keep your garden clean, remove the dead plant matter, disinfect the tools after every use, and filter the air if you are growing indoors. 

The second approach is preventing the growth of verticillium in your cannabis garden if one of your plants is already infected. In this case, you need to cut your losses and remove the entire plant instead of simply removing the infected parts to prevent this fungus from spreading to other parts of your garden. 

Once you remove the plant from your garden, start treating the soil with compost or mycorrhizal fungi as recommended above, and hope that the spores don't travel to other plants in your cannabis garden. This may also be a good time to hasten your harvest as much as you can. 

3. Use Living Soil 

Out in the open, the soil is already living instead of being a dead mass with nutrients in it. But what is living soil? It is a soil with a thriving ecosystem that consists of beneficial organisms, fungi, and bacteria that form a symbiotic relationship with each other and the plant to fix nutrients and protect the plant from harmful pathogens. 

If nature does it, why shouldn't you? So, use living soil in your cannabis garden as much as possible. Living soil is easy to make and you don't have to spend a lot of money for it, either. All you need to do is create an environment in the soil where beneficial microorganisms and insects can thrive, which can be done with compost and mycorrhizal fungi. 

Once the living soil is used, the colonies will work together to prevent the growth of harmful fungi within the soil, including verticillium. In fact, living soil is one of the best ways of preventing verticillium wilt in your cannabis plants. 

4. Maintain Drainage in the Soil 

Once you've set up the soil, you also need to make sure it drains well. This is essential for preventing verticillium since this fungus thrives in soil with dense nutrient concentrations. And let's not forget that a lot of nutrients are already bad for cannabis plants as they can cause nutrient toxicity and lockout. 

So, you need to make sure there is enough drainage in the soil. As a rule of thumb, at least 25% of the water should drain out immediately when you water your plant. If that's not the case, add more drain holes to the container or add perlite and compost to make the soil more airy. You can also consider building a French drain in your garden that uses a 3% gradient. 

5. Use the Right Strains 

So far, experts haven't discovered any cannabis strains that are completely safe from verticillium, but they are trying to find a solution for this. However, there are some strains that are more resistant to diseases in general, i.e., F1 hybrids. 

F1 hybrid strains are more resistant to pathogens and diseases compared to inbred strain lines. They are not totally safe from verticillium wilt, but they are worth a try thanks to their disease resistance in general. Such plants tend to grow a lot better in harsh conditions and don't fall prey to common pests and pathogens as easily as other strains. 

Also, avoid purchasing seeds from random sources. Only use reputable seed banks that offer stabilized strains with genetics. High-quality seeds may cost more in comparison to the cheap ones, but it is worth the extra money you pay for them. 

6. Grow Hydroponically 

By now, you may have noticed that verticillium is more or less a soil problem as it thrives in unhealthy soil. So, perhaps the best way to prevent verticillium is to grow cannabis hydroponically. Hydroponics is a method of growing cannabis without using soil, and this method allows you ultimate control over your cannabis growth. 

There are many types of hydroponics that you can use to grow cannabis, with the best ones being ebb and flow, deep water culture, aeroponics, wick system, etc. Pick your flavor and start growing cannabis with hydroponics and you'll never have to worry about verticillium again. This is recommended for growers that are facing verticillium regularly. 

Summary: How to Prevent Verticillium Wilt When Growing Cannabis

Verticillium wilt is a notorious fungal infection that ruins many cannabis plants every year. The infection begins in the soil when a spore finds its way in, and once it finds a host, i.e., your plant, the spore starts germinating and growing into the roots. After finding its way into the roots, it moves to the xylem, where the fungi start growing and choking the vessels. 

Once it takes hold of your cannabis plant, it stops the plant from extracting the benefits of water and nutrients, leading to symptoms like drought and nutrient deficiencies. This leads to symptoms like wilting leaves, discoloration of the leaves, chlorosis, dropping, leaves, and eventually, the death of the plant. 

If you find your cannabis plant suffering from verticillium wilt, there isn't much you can do to fix the problem. You can hope for the best from your plant, cut your losses, and remove the infected plant immediately if you are growing multiple plants. 

Instead, what you need to do is protect the cannabis plant from suffering from verticillium once again. Here, you need to solarize or pasteurize the soil, treat it with compost and mycorrhizae, use living soil, make sure the soil has good drainage, and use the right strains. 

Lastly, if the problem persists in your cannabis garden, you should consider growing cannabis hydroponically. It allows you the utmost control of your cannabis cultivation without the risk of verticillium. Yes, hydroponic gardening is a bit expensive and nuanced, but once you go hydroponic, you can never go back. 

We post many articles regularly on how to deal with common problems you may face as a cannabis grower, including fungal, bacteria, or other forms of infections. So, stay tuned to our blog for more updates on how to grow cannabis the best way.