Tobacco Mosaic Virus: Cannabis Killer

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What is the Tobacco Mosaic Virus?
December 03, 2020
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So, you’ve never heard of Tobacco Mosaic Virus (TMV)? Lucky you! Actually, most people have never encountered this rare disease, mercifully. Once it infects marijuana plants, it spreads quickly, and there’s no cure. You need to recognize the signs and act FAST.

TMV is a dreaded disease that can destroy your entire crop and can remain in the soil for years. There are some very important steps to take, and we shall outline them for you here.

What Is Tobacco Mosaic Virus?

TMV, also called tobamovirus, is a rod-like positive-sense single-strand RNA virus that infects tobacco and other plants in the Solanaceae family. Once an infestation occurs, it leaves a mosaic-like mottling pattern and discoloration on the leaves.

The choice of name is not indicative of exclusivity to a select species of plants. TMV can also affect at least 200 other species. Unfortunately, this list includes cannabis. The good news is it doesn’t affect humans, but any expectations of huge yields of high-quality cannabis need to be immediately reassessed.

How do you spot the Tobacco Mosaic Virus?

Some plants may act as a carrier, not exhibiting any signs at all. In other instances, the symptoms only appear once the plant undergoes some form of stress, such as a nutrient deficiency or pruning.

Most plants however do exhibit the signs of infection, summarized here:

Color of the Leaves:

  • Light green discoloration between the veins of new growths
  • Yellowing visible between the veins of leaves
  • Yellowing of older growths
  • Mosaic-like mottling with dark and light green patterns
  • Pale stripes in both old and new growths
  • Black, brown, or gray patches or spots
  • Brown, burnt-like edges
  • White, powdery patches

Structure of the Leaves:

  • Wrinkled appearance
  • Elongated
  • Malformation (webbed, coiled, curled)
  • Old leaves falling off
  • Wilting
  • Decay
Tobacco mosaic virus cannabis plant

Other signs include weak, flaccid stems, which may also have a purple or red coloration. Stunted growth indicates the virus has entered an advanced stage.

What is the survival range of Tobacco Mosaic Virus?

TMV is highly resilient and able to survive in environments that do not exceed 104°F and where there are host plants to infect. It has been observed to stay alive for up to 30 minutes in dried leaves at 122°F. This disease can be particularly devastating in a greenhouse because of favorable environmental conditions and the sheer number of host plants.

What are the modes of transmission of the Tobacco Mosaic Virus?

TMV enters the host plant through microscopic channels in the cell walls called plasmodesmata. It then starts to colonize, replicating its genes and spreading throughout the leaves.

It’s usually transmitted to other plants by people: contaminated hands or gardening tools, even clothing. It’s also possible an infected plant might leak sap as a result of an injury, whether deliberately or accidentally. The fluid, which contains the virus, can then be introduced to other plants through direct contact.

Insects and pests are typical vectors of TMV. Aphids, leafhoppers, grasshoppers, and caterpillars, for example, may help spread the disease to other plants.

TMV can also survive in the soil, contaminating seeds and infecting young sprouts and seedlings.

On rare occasions, it can be transmitted through smoke (if a person smokes contaminated buds).

How do you prevent the Tobacco Mosaic Virus?

You could have the best seeds in the world, guaranteed to be of the highest quality, but this won’t stop your plants from contracting TMV. Not even the use of high-end equipment and the best nutrients can stop TMV. The worse thing is that the virus can remain dormant for years in dead tissues and still infect plants far into the future.

The best way to stop TMV is to prevent contact with you, your grow room or the marijuana plants.

You can do this by:

  • Purchasing cuts (if growing clones) from a reputable source, one that has an impeccable track record and high standards. Always inspect each young plant for signs of the disease.
  • If you even so much as suspect that a plant has TMV, act FAST. Immediately remove it from the grow room and away from the other plants. If it does not appear to be serious, keep it in quarantine and observe it for signs of recovery.
  • Use a 10% solution of household bleach to clean and disinfect surfaces and gardening tools to (hopefully) kill the virus before it spreads and contaminates other plants.
  • TMV can be transmitted through your clothes – launder them as soon as possible.
  • If the infection appears to be severe, you should consider discarding old tools and plants as well as the soil.
  • Wash and disinfect hands thoroughly after handling plants infected with TMV.

TMV is deadly but rare

Tobacco Mosaic Virus Crystal

The tobacco mosaic virus has had devastating consequences on several large farms, throughout the years. Fortunately, losses on this scale are not something home marijuana growers have to face. That said, the fact that cannabis can be a host means, as growers, we have to watch out for signs of infection – regardless of whether we’re cultivating 6 plants or 6000.

As Kyle Kushman always says: be observant!!!