Cucumber mosaic virus (CMV) is one of the most common plant viruses and causes a wide range of symptoms, especially yellow mottling, distortion and stunting. Expect damage whenever susceptible plants are growing strongly in spring and summer.

Apart from cucumbers and other cucurbits, CMV also attacks spinach, lettuce and celery and many flowers, especially lilies, delphiniums, primulas and daphnes.

For more on how this virus is transmitted, see the Biology section below.

You may see the following symptoms:

• Yellowish patches or green and yellow mottling on leaves
• Leaves curl downwards and are distorted and reduced in size
• Plants are stunted due to a shortening of the internodes (lengths of stem between leaves)
• Reduction in yields and distorted fruit
• In flowers white streaks known as ‘breaks’ appear

Non chemical control

• Whilst the aphid vectors are the most important way in which the virus is spread, CMV can also potentially be transmitted on garden tools and gardeners’ fingers. Avoid handling healthy plants after working with suspected infected ones until tools or hands have been washed with soapy water
• Destroy suspect plants promptly to reduce the risk of transmission
• Keep the garden weed free. Groundsel and chickweed are particularly likely to harbour CMV
• Choose resistant cultivars. Courgettes ‘Supremo’ and ‘Defender’, bush marrow/courgettes ‘Badger Cross’, ‘Zebra Cross F’ and ‘Tiger Cross’, cucumbers ‘Bush Champion’, ‘Crispy Salad’, ‘Jazzer F’, ‘Paskia Fi’, ‘Petita’ and ‘Country Fair’ and aubergine ‘Bonica’ all show some resistance

Chemical control

There are no chemical controls available to control virues. The use of insecticides to reduce aphid transmission is not practical.

Plant viruses are extremely minute infectious particles consisting of a protein coat and a core of nucleic acid. They have no means of self-dispersal, but rely on various vectors (including humans) to transmit them from infected to healthy plants. Once viruses penetrate into the plant cells they take over the cells’ nucleic acid and protein synthesis systems and ‘hijack’ them to produce more virus.

Viruses are frequently transmitted through propagated material but, depending on the virus, can also be transmitted via insect or mite vectors, pollen, mechanical transfer via contaminated hands and tools, or nematode vectors in the soil. Some viruses can be transmitted via seed, but generally these are a minority and therefore seed propagation is often a useful way to ensure virus free plant material.

CMV is vectored by several aphid species which feed on a broad range of plants and this contributes to spread of CMV to the very wide host range of this virus.

The ‘cucumber’ in its name only reflects the fact that cucumber happened to be the plant from which it was first described. In fact, its host range is extremely wide among vegetables, flowers and some weeds, though fruit crops are rarely attacked. In some weeds the virus produces no symptoms, but these weeds can still act as a source of infection.

CMV is occasionally transmitted through seed in around 20 plant species.