I seem to have been talking about plant viruses quite a bit this last year or two, and the latest plant to suffer from this disease in my garden is a new fig plant. The mottled leaves jumped out at me a week or so ago, made more obvious by the fact that the mature leaves were obviously starting to lose some of their green chlorophyll with the approach of summer’s end. And the mottling I recognised as symptomatic of Fig Mosaic Virus. Bad news.
I’d decided to add another fig to the couple of specimens I already have planted against a sunny wall, and did some research on the hunt for a more unusual variety that you wouldn’t usually find at a garden centre. Deciding on the variety ‘Ronde de Bordeaux’ which produces exotic looking black fruits when fully ripe, I found that it was out of stock in most nurseries, so turned to eBay as a source of a young plant. It cost £14.90 for a small rooted cutting in a 9cm pot – not great value for money, but I consoled myself with the fact that it was the variety I wanted.
Having potted up the young plant, I decided to grow it on outdoors ready to plant out this autumn. And I’m relieved that I did, and that I kept it a long way from my other figs! Once I noticed the disease, there was nothing for it but to destroy the plant to stop the chance of the virus spreading.
This incident has brought home to me, again, the importance of buying from reliable nursery sources, from people who know what they are selling and wouldn’t sell a diseased plant. The fact that anyone can sell plants on eBay or other auction sites gives plant diseases and pests an opportunity to spread – with or without the knowledge of the seller. And it pays to be alert to the appearance of plant viruses, so that we as gardeners can help to limit their spread.
What are plant viruses
Plant virus diseases are common on a range of ornamental and crop plants. The organisms themselves are microscopic so not visible to the naked eye, and are able to spread throughout the whole system of tissues in the plant, and are therefore referred to as systemic. This means that they are contained in the sap itself which makes them very easy to transmit from one plant to another. Different types of virus are generally specific to certain plants.
They have the potential to spread quickly from plant to plant, so it’s best to remove and dispose of affected individuals at the first sign of trouble. It’s not confirmed how the virus is spread, but sap-sucking insects, such as aphids, mites, nematodes and gardening tools, such as pruning knives, are likely contenders.
What are the symptoms of plant virus disease
Signs of plant viruses manifest themselves most obviously in the leaves, stems and flowers of plants. Mottling can be subtle, with marbled streaks or mosaics only visible when the plant is becoming weakened by the disease or lacking nutrients. More obvious yellow streaks and patterns can be seen on tomatoes and beans, in the case of their specific viruses.
Close inspection is needed to spot the early signs and isolated streaks and mottling can be a sign of other pests and diseases. But virus symptoms are usually seen throughout the old and young leaves of the plant.
How to control plant virus disease
There are no ways in which the amateur gardener can control plant viruses. It is important to remove and dispose of affected plants in the rubbish bin or burn them, not put them on the compost heap from where the virus can transmitted to other plants. Prevent spreading the infection between plants when pruning or trimming by wiping the blades of pruning knives with methylated spirits.
Commercially, certain types of plants can be ‘cleaned up’ by growers to get rid of virus disease. In some cases this involves raising new plants from seeds, as virus is less likely to be contained in these. But modern methods of micropropagation – taking a few, very young cells not yet infected with the virus, and growing them on a nutrient jelly in sterile conditions – are used for named varieties and cultivars.
Dahlias and cannas often suffer from their own forms of virus which rears its head each time these plants experience a surge in popularity. Propagating from infected plants readily spreads the disease, but it seems to also be transmitted by sap-sucking insects. Friends and family may unwittingly give you cuttings or divisions of such diseased plants. As always, buy plants from reliable sources.