What You Should Know About Mosaic Viruses

Mosaic viruses affect many different types of plants grown in your garden. These include tomatoes, cucumbers, peppers and fruits such as grapes, bananas and papayas. Find out how to identify this virus and what to do about it.

What Are Mosaic Viruses?

The term Mosaic Virus is a broad description of many plant viruses that can cause mottled and deformed foliage on at least 150 agricultural and ornamental crops. Home gardeners are most likely to encounter viral problems with a handful of plants that they grow, most likely tomatoes, cucumbers, squash, and beans in their gardens. Still, there are mosaic viruses that affect many other important plants such as fruit (grapes, papayas, and bananas), grains (such as corn, rice, and oats), and even certain houseplants (poinsettias, freesias, and orchids), to name a few.

With dozens of species-specific Mosaic Viruses found worldwide, there is one thing that they all share in common – there is no cure. That said, there are proven ways to eliminate the virus from one’s garden and ways to avoid an outbreak.

Garden Plants Most At Risk

Tomato

The Tomato Mosaic Virus (ToMV) – The Tomato Mosaic Virus (T0MV) is so closely related to the devastating Tobacco Mosaic Virus (TMV), that without submitting samples to a plant disease laboratory, identifying and diagnosing exactly which virus your plants may be suffering from can be nearly impossible. However, the symptoms of most Mosaic Viruses appear identical, their treatment is typically the same.

Look for these tell-tale symptoms and signs on tomato plants (as well as the other crops affected by ToMV and TMV, such as cucumber, pepper, petunia, tobacco and lettuce.).

Cucumber

While cucumbers are also susceptible to Tomato and Tobacco Mosaic Viruses (they are all closely related), they also have their own Mosaic Virus. The Cucumber Mosaic Virus (CMV) affects most plants found in the squash and melon family (Cucurbitaceae). While cucumber crops, in particular, are affected by CMV, this special virus also attacks other crops, including lettuce, peppers, beans, celery, and spinach. It’s easy to see why identifying each Mosaic Virus can be challenging, but how you treat affected plants and solutions is relatively the same.

The cucumber Mosaic Virus manifests itself slightly differently from the tomato and tobacco viruses, but it still includes the typical deformed foliage and miscolored leaves. Affected plants typically start showing symptoms with immature or chlorotic foliage (extreme yellowing of the leaves) followed by curling and distorted young leaves that often appear thread-like. Flowers may abort before bearing fruit, and any fruit that does mature will usually exhibit roughly textured skin.

Pepper

Pepper Mosaic Virus (PMMoV). The pathogen that affects peppers often called the Pepper Mosaic Virus is also known as the Pepper Mild Mottle Virus (PMMoV). Its symptoms are similar to other TMV and are considered closely tied to the entire Tobacco Mosaic Virus family. The Pepper Mosaic Virus is unique to peppers (whereas the Tobacco Mosaic Virus affects all most plants in the tomato family (Solanaceae). Spread mainly by infected seed, it’s the single major pathogen affecting pepper crops worldwide.

How Do Mosaic Viruses Spread?

All of the mosaic viruses spread quickly. Most commonly, transmission occurs via humans as they handle infected plants. Cross-contamination can also occur from gloves, tools, and even clothing, so cleanliness is essential. The virus is also easily spread by contaminated seeds. Since the virus can live in soil for a few years, never re-plant the same crop where infected plants once grew a year or two earlier.

How to Prevent Mosaic Viruses

The best prevention is to remove and destroy infected plants, rotate crops, sanitize and disinfect any tool or material that came in contact with the disease.

While no plant is known to be 100% immune to any specific Mosaic Virus, many hybrid plants or selected ones can be relatively disease resistant. Look for disease-resistant varieties of tomato, bean, and cucumber in seed catalogs and on plant labels. The codes for disease resistance are usually listed at the end of a description. For example, some tomatoes highly resistant to ToTMV and TMV are ‘Sungold’, BHN-444, and ‘Big Beef.’

Tobacco is a significant vector in spreading many Mosaic Viruses. Avoid handling plants if you smoke cigarettes or use any tobacco product. The TMV virus particularly lives on dry tobacco and can easily be spread from fingertips to plants, even to houseplants.

How to Get Rid Of Mosaic Viruses

While you can eliminate the virus from their garden quickly, there is no guarantee that the virus will not return. There is no fungicide that will be effective because the problem is a virus, not a bacteria or fungus. While insects can introduce or spread the pathogen from a neighboring garden that has infected plants, use of pesticides is not effective nor recommended.

You can casually introduce the virus via infected seed as the virus can lay dormant on a dry seed coat for years. Look for seed that has been heat treated or hot water treated. Be cautious when saving your own garden seed or when purchasing seed from private sellers online who may not have sterilized their seed correctly.

More often than not, the virus will appear unexpectedly with no fault of the gardener, as an infected tomato or pepper plant often won’t show the tell-tale mottled or deformed foliage until the plant is nearly mature during the heat of summer. It’s rarely seen on young plants or during cold or wet weather. Remove any infected plants once discovered.

If a crop exhibited the virus in one season, rotate the bed or garden with crops that are not susceptible to the virus for at least two years, or allow the bed to lay fallow. Clean and sterilize anything that came in contact with the plants with a 10% bleach solution, including garden tools, gloves, and even staking material. Growing crops in sterilized potting soil and clean containers will also improve results. Never reuse old potting soil from a previous season.

Take care when cleaning the garden in the fall. Dispose of any affected debris properly (burn or trash, and never introduce it to the compost bin). Be sure to remove any roots and underground parts for plants like potatoes to ensure that none of the pathogens remain within decaying plant material.