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Cannabis Viruses: What Are They And How Do They Affect Your Plants?

Added 28 February 2023

We always worry about our cannabis plants being affected by pests, mold, fungi, and other common diseases. But when was the last time you worried about your plant suffering from a viral infection?

Probably never, and you’re not alone. But it is time to start worrying about viruses. 

According to experts and researchers, cannabis viruses are widespread in cannabis gardens across the world. For example, experts conducted over 200,000 tissue tests on cannabis plants across California and found that approx. 30% of the plants suffered from hop latent viroid (HLVd), one of the common plant viruses that affect cannabis.

Translating this number to a national scale in the US — that’s a loss of over $USD 4 billion annually due to this single virus! Imagine the loss the cannabis industry faces across the world due to this and other viruses. 

What are these viruses and how do they affect cannabis plants? And can you do something about it? 

Read this article to know all about the common viruses that your cannabis plant may suffer from. 

What are Viruses?

What are Viruses?

Viruses are perhaps one of the most mysterious organisms on earth —– if we can call them living organisms in the first place! Their origins are still shrouded in mystery, but experts believe that viruses originate in one of three ways

The three theories on their origins are:

  1. Regressive hypothesis, where a small cell once fed off of another larger cell, making the latter lose a part of its genetic material.
  2. Cellular origin hypothesis, where viruses evolved from bits of DNA or RNA from other larger organisms.
  3. Coevolution hypothesis, where viruses evolved from protein molecules and nucleic acid.

Regardless of their origins, viruses are pretty straightforward organisms. The viruses that affect plants are intracellular and need a host cell to replicate. 

According to experts, viruses that affect plants follow a five-step protocol:

  1. They begin by infecting the host plant.
  2. Evade immune plant cells.
  3. Head to the target cells in the plant body.
  4. Start multiplying. 
  5. And repeat the process until they have overtaken the body. 

Of course, the actual mechanism of these viruses is a lot more complicated, though this is the basis of it. The virus needs a living host to live and multiply, and as a result, it ends up damaging the body. 

While we know hundreds of viruses that affect humans, we don’t know many that affect plants like cannabis. So far, experts have only discovered a few. One of which is the tobacco mosaic virus (TMV), which was discovered by Adolf Mayer in 1886. 

What experts are sure about is that these viruses are specific to a certain species as they need a particular type of host cell to replicate. This means plant viruses have a few hosts that can sustain them. And cannabis is one of them for a few specific plant viruses. 

How Do Viruses Affect the Cannabis Plant?

How Do Viruses Affect the Cannabis Plant?

Viruses, like bacteria, cause various diseases in the cannabis plant or hamper its physiological process, which can affect how the plant grows, develops flowers, or protects itself from environmental dangers. 

The common cannabis viruses, including tobacco mosaic virus, hop latent viroid, cannabis cryptic virus, beet curly top, lettuce chlorosis virus, etc. can display various symptoms in your cannabis plant, such as the following:

  • Stunted or slow growth of the plant. Viral infections can cause stunted growth, reduce the size of leaves and buds, and ultimately decrease the yield of the plant.
  • Discoloration and spotting: Some viruses can cause discoloration and spotting on leaves and other parts of the plant, which can reduce the overall health and appearance of the plant.
  • Weakened immunity. Viral infections can weaken the plant's immune system, making it more susceptible to other diseases and infections.
  • Brittle stems that can snap easily. 
  • Poor bud development, resulting in small, airy buds.
  • Chlorosis or leaf malformations.
  • Reduced cannabinoid and trichome production, resulting in low potency and flavor profile. 
  • Overall bad quality of the yield. 

Viral infections can significantly impact the growth, health, and yield of cannabis plants. Prevention and early detection are crucial for managing viral infections in cannabis cultivation, as there is no cure for viruses once a plant has become infected.

In some cases, viruses can also kill your plant if you don’t take the right steps at the right time. And the damage is not limited to one plant — viruses can spread fast to your entire garden, affecting all your cannabis plants. More on this below.

How do Viruses Spread in Cannabis?

How do Viruses Spread in Cannabis?

Ask an expert and they will give you a complicated answer on what a virus actually is, because, in a biological sense, viruses don’t seem like living organisms at first. They are protein capsids that contain genetic material but they can’t move from one plant to another. In fact, they are not even “alive” unless they enter a host cell.

So, how can they travel fast and affect entire gardens of cannabis if they are not “alive”? The answer is viral vectors — living beings (or things) that carry these viruses from plant to plant, finding new hosts for them. 

Once they reach a new host cell, they lose their protein capsid and begin replicating quickly. The subsequent generation of viruses still contains protein capsids so the virus can move to another host plant. 

Here are some of the common ways viruses travel in a cannabis garden.

1. Mechanical Transmission

If you are a serious grower, you probably use some basic gardening tools to tend to your cannabis plants, like scalpels, trellis netting, and pruning scissors. These are common viral vectors for cannabis viruses as they can carry the virus from the infected plant to other plants. 

If you don’t sanitize the equipment properly between uses, it can spread viruses from one plant to another. So, it’s important to make sure your equipment isn’t contaminated. Also, if the soil or water used to grow cannabis is contaminated with a virus, it can infect the plants.

2. Clones or Cuttings

If a clone or seedling is infected with a virus, it can spread the virus to the entire plant and any plants it comes in contact with. Viruses like lettuce chlorosis virus (LCV) and HLVd tend to spread through cuttings from an infected mother plant used for cloning cannabis. This process speeds up the spread of viruses that may have not shown any symptoms on the mother plant, yet, making it tricky to identify and easy to spread.

3. Lack of Proper Quarantine 

Another common way of spreading plant viruses to a grower’s garden is if you don’t quarantine new additions before introducing them to your garden. This is where disease testing and quarantining are essential for those who grow multiple plants. 

4. Pests

Pests are another common vector for such viruses. According to studies, LCV is the most common virus that spreads via such pests, especially whitefly. Other viral vectors include thrips, aphids, or mites. 

In fact, sometimes, even the grower themselves may act as a vector by carrying the viruses to the garden and spreading them!

5. Seeds

An uncommon vector is the seeds. According to various studies, seeds tend to transmit hop latent viroid at approx. 8% transmission rate. Even the cannabis cryptic virus is known to spread via seeds. 

Once a plant is infected with a virus, it can be difficult to control the spread. So, you need to practice good sanitation practices, use clean soil and water, and monitor your plants for signs of infection. If you find an infected plant, remove it and destroy it to prevent the virus from spreading to other plants.

What are the Common Cannabis Viruses?

What are the Common Cannabis Viruses?

We have mentioned some of the common cannabis viruses already in the article, but let’s dive a little deeper into them and how they may affect your plant.

1. Tobacco Mosaic Virus

Tobacco mosaic virus (TMV) is one of the most common plant viruses that primarily infect tobacco plants but it can also infect other 125 species of plants belonging to nine families, including the cannabis plant. 

The tobacco mosaic virus’ capsid contains over 2,000 molecules of coat protein and a single molecule of genomic single-strand RNA. Once this virus finds a host in a cannabis plant, it loses its outer capsid and releases the viral RNA in the plant’s tissues, which quickly starts replicating itself. 

Generally, TMV and its strains tend to cause various symptoms in the cannabis plant, starting with discoloration between the leaf veins — many growers initially confuse this with nutrient deficiencies.

The difference between TMV and nutrient problems becomes clear once this viral infection worsens — the plant develops mottling that resembles a mosaic, hence the name. 

In some cases, the leaves of your plant can also develop rugosity and wrinkles and can become contorted or curved. Over time, the lower leaves also experience the damage of mosaic burn, especially in hot or dry climatic conditions.

Eventually, most leaves die and the plant stops growing entirely. 

One thing that makes TMV so deadly for cannabis is that it is one of the most stable plant viruses. As long as the temperatures stay above 104°F or 40°C, it stays stable. This makes greenhouses and botanical gardens an ideal spot for TMV to spread, thanks to their constant temperature and multiple hosts.

2. Hop Latent Viroid

Hop latent viroid is an unfortunate result of the legalization wave of 2012 in the US. in 2017, a grower in California first noticed the symptoms of this virus, including brittle stems and yellow leaves, on one of their crops. Soon, experts discovered that this virus that originated in California had quickly spread to various gardens across the country. 

Also known as HLVd, this is a pathogen that is RNA-based, just like TMV. Despite being on this list, HLVd is not really a virus — it is categorized as a viroid because it does not have the protein coat that TMV or other plant viruses do. 

As you may have already guessed, hope latent viroid was first found in the herb called hops (popular as an ingredient for beers), but over time, growers across the world have also found this virus in cannabis plants. So much so that HLVd has become a common virus that plagues the cannabis plant species. 

When it finds a host in a cannabis plant, it causes dudding — a term that describes a variety of symptoms like:

  • Vigor loss in cannabis
  • Slow or stunted growth
  • Reduced yield due to poor bud development 
  • Reduced cannabinoid and terpenoid production, leading to a loss in potency and flavor 
  • Unnatural changes in the plant’s morphology 

According to experts, a plant infected with this virus can lose 50% to 70% of its THC (and other cannabinoids) content!

Because of these effects, you must screen your cannabis plants for any early signs of HLVd to ensure it does not spread to other plants in your garden. This especially holds true when cloning cannabis from a mother plant. This virus has a long latency period, so the symptoms don’t develop right away. 

Along with the difficulty to detect this virus, it is also quite difficult to eradicate it from your garden once it has been contaminated. At a glance, your cannabis may seem completely healthy but they are asymptomatic. Over time, most of your plants will start displaying the symptoms of dudding.

Expert growers recommend screening mother plants often since cloning is the most common vector for this virus. 

3. Lettuce Chlorosis Virus

LCV, short for lettuce chlorosis virus, is another RNA-based plant virus that, given its name, is usually encountered in lettuce but it can even contaminate your cannabis plants. It is a member of the Crinivirus family. 

One of the primary symptoms of this virus in cannabis is leaf chlorosis, where the leaves turn yellow since there isn’t enough chlorophyll. If your cannabis is infected with this virus, it will eventually fail to grow as it won’t have enough chlorophyll to sustain itself, even if you place it under 10 grow lights. 

Unlike the two viruses mentioned above, LCV produces a more drastic impact on cannabis, making it look sick and unhealthy quickly. Additionally, LCV can sometimes display comparable symptoms to HLVd.

4. Beet Curly Top

Another common virus is BCTV, and unlike other viruses in this list, BCTV is DNA-based and originally infected sugar beet plants, but it has now spread to other species of plants. 

As the name suggests, the primary symptom of this virus is that it can cause cannabis leaves to curl, altering the photosynthetic abilities of your plant. And, no, BCTV does not cause regular curling — the leaves curl completely until they almost resemble an ice cream cone!

The result is a plant that grows slowly due to low energy and produces a poorer yield than expected. 

The only known vector for BCTV is beet leafhopper, which carries the virus from an infected plant to other hosts in the vicinity. And since this virus does not affect the insect, it is highly mobile and difficult to completely eradicate from a cannabis garden. 

These are just some of the common cannabis viruses that we have discovered so far; other viruses that are not so common in cannabis include hemp mosaic virus, hemp streak virus, tobacco ringspot virus, tobacco streak virus, alfalfa mosaic virus, and Arabic mosaic virus. 

5. Cannabis Cryptic Virus

CCV is a double-strand-based RNA virus belonging to the Partitiviridae family, and this virus has been quite an enigma for experts for years. No wonder it has the word “cryptic” in its title, doesn’t it? 

A weird thing about this virus, unlike other viruses on the list, is it does not really cause any pathological impact on the plant — it is atypical. And it is commonly found with other viruses in the cannabis plant.

In fact, some anecdotal reports even suggest that this virus may add pathology to the plant. For example, if your plant is contaminated with CCV along with HLVd or LCV, the former may alter the way the other virus acts in the plant. 

The most common vector for CCV is seeds, i.e., it can spread from the seeds to a seedling and keep spreading in the following generations. This transmission is known as vertical transmission. 

To prevent this virus, you must screen your crop and seeds before breeding them. 

What are the Treatment Options for Cannabis Viruses?

What are the Treatment Options for Cannabis Viruses?

There isn’t a lot you can do once one of these plant viruses infects your cannabis plant. Generally, experts recommend you cut away any dead plant material along with any parts that look infected. The next step is to quarantine the plant so the virus does not spread to the other plant. 

There is no supplement, fertilizer, or any other remedy that can cure your cannabis plant from such plant viral infections. 

This is why you must prevent these viruses from ever finding their way into your garden and onto your cannabis plants. You can do this by choosing strains that are resistant to viruses, keeping the plants in a healthy environment, isolating and quarantining new plants, and keeping the viral vectors in check. 

Read on to know more about tips and tricks to prevent viruses from attacking your cannabis plant.

How to Prevent Viruses on Cannabis Plants?

How to Prevent Viruses on Cannabis Plants?

If you want to save your cannabis plant from suffering a viral infection, you need to be proactive and employ sustainable disease management techniques. As a cannabis grower, you can take a multi-pronged approach to mitigate this risk, and here are some of the best ways of doing so. 

1. Choose a Virus Resistant Strain

Genetics play a big role in growing cannabis — more so than most growers give it credit for — and it can sometimes make your plant safer from viral infections. Some cannabis strains are genetically resistant to viral attacks and have internal mechanisms that slow down the replication of such viruses. 

2. Keep Your Garden Clean

The next step is to be strict about sanitation in your cannabis garden, whether you’re growing cannabis indoors or outdoors. One of the easiest vectors for plant viruses is any cut on your plant — it gives the virus easy entry into the plant’s vascular system.

So, you must use fresh, sterile blades any time you are working with your plant. And take the right steps to conceal or protect the fresh wounds on your plant from external factors like bugs, contaminated air, or yourself. 

There are various ways to sanitize your tools. Whether you make a disinfectant at home or purchase one meant to sanitize garden tools, it’s a must to keep your tools clean. After all, one piece of equipment can destroy your garden if you aren’t paying attention, so follow these guidelines just to be safe. 

First, disinfect your tools using a household product like Lysol that’s easily available in most stores. In addition, these disinfectants are typically non-corrosive so you don’t have to worry about ruining your tools. However, the effectiveness of such products hasn’t been researched extensively, so it’s a hit or a miss. If you decide to use a household disinfectant, apply it at full strength using a spray or dip, but follow the label instructions.

Another disinfectant that’s easy to find yet affordable is chlorine. However, it is corrosive and can produce harmful fumes. It is also less effective against viruses compared to other products, so go for chlorine only if you have no other options.  

You can also use bleach to sanitize your equipment. To make a bleach solution, mix 1 part of bleach with 9 parts water and let the tools soak in this solution for about 1 hour. And, you’re done. But, keep in mind that this solution could lose its effectiveness very quickly in just under two hours, so we recommend that you make fresh batches every time you want to sanitize your tools with bleach. Also, rinse your tools thoroughly with clean water after soaking to prevent corrosion.

Finally, you can use alcohol to get rid of unwanted stuff on your equipment. Alcohol, including isopropyl or ethanol, can be used conveniently to protect your plants. One advantage is that you can pour some alcohol on a cloth and wipe it on the tools for quick results. However, be careful while using alcohol since it’s extremely flammable. 

Tool sanitation not only keeps your plant protected from viruses but also from other diseases that may arise from bacteria or fungi. You can use any tool-specific disinfectant to sanitize your tools, but one of the best DIY disinfectants is an alcohol mixture. 

Apart from the tools, you must also keep the garden clean from any debris, dirt, or pathogens. Even your vents and fans must be clean and they should ideally prevent any bugs from making their way into your grow room.

3. Control Pests in Your Garden

Speaking of bugs, pests are one of the most effective vectors for plant viruses, along with many other diseases. Some pests are nasty enough to damage your plant on their own, too. 

So, you must also control pests in your garden. The most notorious pests include aphids, thrips, mites, whiteflies, etc., which are a nuisance to deal with even if they don’t carry any viruses on them. 

There are various strategies you can use to keep these pests out of your garden, including companion planting, neem oil, or pest traps. Employ these tactics to keep your plant safe from pests.

4. Quarantine New Plants 

If you grow multiple plants and add new plants to the garden regularly, you should have a designated quarantine area for the newer plants. The quarantine area must be sterile and isolated from the main garden, and here, you can keep your new additions, clones, or mother plants and test them for any viral infections or other diseases.

In this situation, a diagnostic screening test is quick and efficient to find any viruses on the plant. If it shows any positive result, you must eliminate the plant from your garden and sanitize the quarantine area again before adding new plants to it. 

If you don’t have access to a diagnostic screening test, you can simply keep the plants in the quarantine area for a couple of weeks and check for any signs of viral infections. It is slow but also effective.

Summary: Cannabis Viruses: What Are They And How Do They Affect Your Plants?

Cannabis viruses are tricky to identify — they may stay asymptomatic for long enough for the virus to travel to other plants in the vicinity, and when the symptoms appear, it may be too late to save your plant. 

Fortunately, in recent years, perhaps thanks to the COVID-19 pandemic, growers across the world are taking viruses seriously. In the past, no one cared much about these viruses, and any symptoms of viral infections were chalked up to some other ailment. 

It is not too late even now. Despite plant viruses being common, they are still somewhat of an occasional appearance in cannabis plants. And while there is no way to treat a viral infection in cannabis as of today, there are a few easy ways you can prevent them entirely.

Remember, there is no cure for viral infections in cannabis plants. Once a plant is infected, the virus will continue to replicate and spread throughout the plant. However, there are some steps that can be taken to manage the symptoms of the infection and prevent it from spreading to other plants.

Keep these points in mind to prevent viruses from ruining your yields:

  1. Quarantine infected plants: Isolate infected plants to prevent the virus from spreading to healthy plants.
  2. Remove infected plants: If a plant is severely infected, it should be removed and destroyed to prevent the virus from spreading to other plants.
  3. Practice good sanitation: Regularly sanitize all tools, equipment, and surfaces used in cannabis cultivation to reduce the risk of transmission.
  4. Use disease-resistant strains: Consider using strains that are known to be resistant to certain viruses.
  5. Monitor plants closely: Keep a close eye on plants for signs of infection and respond quickly if symptoms are observed.

Prevention is the best approach to managing viral infections in cannabis plants. These basic things will help you prevent most of the viruses from ever finding their way into your garden.