Can Tobacco Mosaic Virus (TMV) spread to cannabis plants? Some growers believe mosaic virus can infect weed, yet actual evidence of cannabis transmission is hard to come by.
What is Tobacco Mosaic Virus anyway? TMV is a virus that is commonly found in tobacco plants which causes splotchy or twisted leaves, strange mottling symptoms (a "mosaic"), slowed growth, and reduced yields. Mosaic virus has spread to several other species of plants besides tobacco, and some people believe cannabis plants may be able to catch mosaic virus, too.
Note: Mosaic virus won’t hurt you, but plants that get infected by mosaic virus may not grow as fast or yield as well as they could have.
Did you Know? Tobacco Mosaic Virus was the first virus ever to be discovered.
The mosaic virus was first identified in tobacco plants in 1892 but is now known to infect at least 125 species of plants, including tomatoes, peppers, cucumbers, and many types of flowers. It can live in the soil but mainly travels from plant to plant by direct contact. It can also be transferred from one plant to another via your hands. Some growers have claimed to see the symptoms after exposing their plants to tobacco.
The mosaic virus can attack a wide range of plants, but has it spread to our beloved herb marijuana?
Here’s a pic of a tobacco plant with confirmed TMV – the mottled leaves are the main symptom of the virus besides overall slow growth.
Here’s a pic of a squash plant that has caught Mosaic Virus
Euphorbia viguieri plant infected with mosaic virus
Several leaves throughout the plant can display symptoms, or it may just be one or two leaves. Typically the twisted growth is accompanied by a speckling/mosaic pattern. To make things complicated, some plants are silent carriers and may never show any symptoms.
Can Cannabis Plants Catch Mosaic Virus?
Now the real mystery. Can mosaic virus spread to cannabis plants? And if it can, what are the symptoms and how do you get rid of it?
Is there a "cannabis mosaic virus" out there? Some growers believe mottled leaves could be signs of the virus in cannabis plants
I’ve included several pictures of the symptoms that many marijuana growers believe to be the result of mosaic virus. Symptoms include twisted or curved leaves, yellow stripes, spots, and a mosaic pattern. Yet these symptoms could also be caused by plant problems such as heat, root rot, stress, nutrient deficiencies, etc. There’s also the possibility of a mutation or other genetic factors.
The most common symptom attributed to TMV is the appearance of uneven stripes on leaves of light and dark green. Yellowing is worse on the parts of the leaves that are deformed and twisted. The dark green areas tend to be somewhat thicker than the lighter portions of the leaf.
Curved leaves with yellow stripes or mottling are the most common symptom attributed to mosaic virus.
TMV-affected plants are said to grow slow, seem sickly, and generally produce poor yields.
Some growers swear their crops have been greatly affected by TMV, while others deny that it’s actually even spread to cannabis plants at all. The mosaic virus can be difficult to test for, even in a lab. The main problem with TMV is that it may cause plants to grow slowly and produce poorly. If your plant is growing fast and healthy, with no other symptoms, and you’re not noticing it spreading from plant to plant, you probably shouldn’t get too worried.
The cannabis pictures presented today appear to follow the symptoms of mosaic virus in other plant species, but none of the cases have been confirmed. What do you think? Just regular plant problems or something more?
Do these cannabis plants have mosaic virus?
At this point, cannabis growers haven’t confirmed that these leaf symptoms are caused by mosaic virus or something else
Unfortunately, few cannabis growers have the equipment or the means to test if a plant actually has TMV.
Can TMV spread to cannabis plants? No one knows for sure, but...
- Not much evidence – There isn’t much concrete evidence that cannabis plants can catch mosaic virus besides anecdotal reports
- Tests often come back negative – The Florida Department of Agriculture has tested several cannabis and hemp plants showing symptoms, yet none tested positive for mosaic virus. If you know of any positive tests for mosaic virus in cannabis, please let us know!
- Similar symptoms to other problems – Many common issues can cause similar symptoms, including incorrect pH, watering problems, root problems, deficiencies, etc.
- Affected plants don’t always seem infectious – I’ve had a few plants display these symptoms over the years. When I saw the symptoms, I tried to "infect" other plants in the grow tent by rubbing their leaves together with the affected seedlings, and it never spread to the other plants. I’ve spoken to several other growers who’ve had similar experiences where they see symptoms on one plant but it never infects the rest of the grow room.
- Could be genetics – Following on the last point, it’s possible the symptoms are sometimes the result of genetic variation. For example, I grew a few plants of a strain called "Purple Sunset" and all the seedlings displayed the mottling and stripes. Yet the symptoms never spread to the several other plants in the grow tent. About a year later, I germinated more Purple Sunset seeds and saw the symptoms again. Just like the first set, the seedlings grew fast and healthy, but some of the leaves showed the odd stripes. I contacted the breeder about it, and he told me that he’s noticed some seedlings of this strain do that when grown under LEDs. To me, this is evidence the symptoms may be triggered by genetic factors as opposed to a virus.
The red arrow in the picture below points to a Purple Sunset seedling with mosaic stripes on the leaves. I tried rubbing the leaves on the other plants, but the symptoms never spread. The seedling grew fast and healthy despite the stripes, and after a few weeks the leaves started growing normally.
Here’s a closeup. Other Purple Sunset plants from the same batch of seeds produced the same markings as seedlings, but (again) didn’t seem contagious. Were the markings the result of genetics?
Conclusion: I personally have not seen convincing evidence (yet) that mosaic virus has spread to cannabis plants. The traditional TMV symptoms can be caused by other factors and sometimes appear on otherwise healthy plants without signs of spreading. That doesn’t mean cannabis plants can’t get mosaic disease, but the appearance of mottling isn’t necessarily a cause for alarm.
This cannabis plant has yellow spots or speckles that appear on the unhealthy parts of the leaves. Is it mosaic virus? Probably not.
But what if the virus can infect cannabis plants? Just because the symptoms aren’t always caused by mosaic virus doesn’t mean the symptoms are never caused by mosaic virus. Shouldn’t you be worried?
If you look at the big picture, the main worry with mosaic virus is that your plants become sick and slow-growing. That means there’s really no problem if affected plants are otherwise healthy and fast-growing without any sign of spreading.
Don’t worry about TMV if...
- Affected plants are otherwise healthy and fast-growing
- Symptoms aren’t spreading from plant to plant
- It seems to be genetic (for example common among all plants of a strain) but you’re not seeing symptoms on unrelated plants
- You think another problem may be causing the symptoms, such as nutrient deficiencies, root problems, heat stress, etc.
A plant virus can be hard to pin down, since many factors cause similar symptoms. Just remember that (if it does exist) mosaic virus appears to be relatively rare in marijuana plants.
How do you treat a cannabis plant has mosaic virus?
We’re not sure if marijuana even can catch TMV, but if you believe you’re seeing an infection, you likely should treat it the same as other types of plants that catch mosaic virus.
Now here’s the bad news. Unfortunately, when it comes to mosaic virus, there is no cure. An infected plant will have TMV forever, even if it’s not actively showing symptoms. If you believe you have a marijuana plant with TMV, your main goal is to prevent it from spreading to other plants.
In greenhouse and commercial operations, the main way to deal with mosaic virus is to dispose of all affected plants, including any soil they were growing in, and enforce a strict policy of hand-washing between touching plants. Luckily TMV probably won’t kill your plants, and there’s no evidence it will hurt you, but if infected plants grow slower and end up producing smaller yields, you definitely want to keep them out of your marijuana garden.
Could the Symptoms be Caused by Something Else?
Some cannabis plants may show mutations such as variegation (two-toned leaves), and this normal and natural phenomenon may be confused for TMV. One difference is the plant otherwise grows fast and healthy.
Two-toned leaves (variegation) is a common mutation. Nothing to worry about if plants are otherwise healthy and fast-growing.
Thrips are a common plant pest which can cause leaf symptoms that are reminiscent of mosaic disease symptoms
Because other plant problems can cause similar symptoms, it’s always a good idea to investigate and see if it might be something else!
Background: How Does TMV Spread?
"Mosaic" disease is caused by a virus. The tobacco mosaic virus is very stable and can persist in contaminated soil, in infected plant debris, on or in the seed coat, and in manufactured tobacco products. The virus is transmitted readily from plant to plant by mechanical means.
This may simply involve picking up the virus while working with infected plant material, then introducing it to healthy plants by rubbing or brushing against them with contaminated tools, clothing, or hands.
Virus plant diseases cannot be "cured" once a plant is infected!
Therefore, every effort should be made to prevent the introduction of virus diseases into the garden.
Sanitation and cleanliness are the primary means of controlling virus diseases. Infected plants should be removed immediately to prevent spreading the pathogen. The use of tobacco products during cultural practices should be avoided to prevent infecting plants with tobacco mosaic virus. Anyone who uses tobacco or works with infected plant material should wash their hands thoroughly in soapy water before handling marijuana plants.