Tomato mosaic virus: what it is and how to treat it

Tomatoes are an ever-present sight on family vegetable patches. They are one of the go-to vegetables that every novice grower tries their hand at: besides offering salad and paste varieties to cater for all tastes, they are easy to grow and provide an abundant harvest.

Various phytopathologies (plant diseases) affect the tomato: fungal pathologies are the most common, although diseases caused by bacteria and viruses should not be overlooked. Physiopathologies are also frequent, that is, tomato diseases caused not by harmful organisms but by factors such as nutritional imbalances, or unfavourable weather and climate conditions. Today we will talk about the most prevalent viral disease of tomatoes, the so-called tomato mosaic virus.

What causes tomato mosaic virus?

Tomato mosaic virus (ToMV for short) is an infectious disease of tomatoes and one of the most widespread viruses affecting this vegetable, of which various strains are known.

The tomato mosaic virus is transmitted mainly by contact, such as with diseased plants and contaminated surfaces (tools, hands, etc.). Contagion by contact occurs through small lesions on healthy plants: due to the ease with which the disease spreads, caution should be exercised when transplanting and pruning. When it contains remnants of diseased plants, the soil itself can become a source of infection, contaminating the roots of healthy plants. ToMV is also transmitted through the seeds of infected hosts.

In addition to the tomato, the mosaic virus attacks other species, which in turn can spread it to other hosts: the main plants at risk are pepper, petunia, snapdragon, marigold and tobacco. Unlike other tomato viral diseases – such as plant decline caused by cucumber mosaic virus and alfalfa mosaic virus – ToMV is not transmitted by aphids.

What are the symptoms of ToMV? The outward signs of infection depend on the specific viral strain and, sometimes, on environmental variables such as temperature. Damage most commonly occurs on the leaves, which show mottled light green and dark green spots – rather like a mosaic effect – and deformations such as bubbling and crinkling. Other strains also alter the appearance of the leaves, while still others affect only the fruits – i.e. the tomatoes – or the entire plant (stem, leaves and fruits).

How to guard against ToMV

One of the reasons why plant viruses are dangerous is because there are no specific pesticides to counter them. Therefore, since there are no targeted treatments against tomato viral diseases including ToMV, prevention is the best way to combat them:

• Choose ToMV-resistant tomato varieties: the seed packet indicates the plant’s level of resistance to various pests and diseases, including ToMV.

• Sow seeds directly in the vegetable patch rather than transplanting pre-grown seedlings, which may have been exposed to infection while in the nursery (from other seedlings, soil, containers, tools, etc.). Use healthy seeds.

• Plan your vegetable patch long-term to ensure that the tomato plants do not always occupy the same plot of ground every year (crop rotation), so as to hinder the spread of diseases and parasites to which they are susceptible.

• Make sure that the soil of your allotment or vegetable patch is free from the remains of infected tomato plants and other host species of ToMV, which is capable of remaining active for months. Hence it is important to till the soil in autumn (using manual tools or a rotary tiller) and then tidy your vegetable patch to remove the remains and roots of previous crops.

• Check your tomatoes regularly for symptoms of mosaic virus: monitoring is an integral part of crop care (as are irrigation, fertilisation and so on). Also monitor any other plants that are vulnerable to ToMV, such as peppers.

• Eliminate diseased plants immediately and dispose of them well away from the vegetable patch: there must be no leftover remains, including in the soil. Prompt intervention greatly reduces the spread of the virus.

• Also keep weeds near the vegetable patch under control through mowing, as appropriate, with a brushcutter, lawnmower, garden tractor or wheeled brushcutter (mowing is one technique for eliminating weeds without using herbicide, just as false sowing prevents them from invading the plant beds).

• Disinfect the tools you use on the vegetable patch with bleach – your pruning shears, for example – and wash your hands with soap and water before handling the plants.

You can easily grow some varieties of tomato in pots: it is one of the vegetables typically grown in vertical balcony gardens. In this case, beware of reusing pots and soil left over from past seasons: used pots must be disinfected, whereas used soil should be replaced with new substrate.

We mentioned that tomatoes are a common sight in domestic vegetable patches: here is our guide to growing tomatoes along with suggestions for keeping your vegetable patch healthy in winter and protecting it from heat in summer. Lastly, it’s a fact that growing vegetables relieves stress, and you also get satisfaction from producing your own food to meet your family’s needs, at least in part.