Disease
Plant viruses
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Watch for | Watch for in April | Watch for in May | Watch for in June | Watch for in July | Watch for in August | Watch for in September | Watch for in October |
What it is
Plant viruses are microscopic particles that multiply inside living cells. Hundreds exist, and between them they affect almost every plant in the garden. Some cause little more than a mild mottle; others stunt plants badly or ruin crops. A few, such as the one that streaks tulip petals, were once prized for the effect they create.
Symptoms
Typical signs are a yellow and green mosaic or mottle on the leaves, pale streaks or rings, crinkled, cupped or narrowed leaves, and stunted growth. Courgettes with cucumber mosaic virus have yellow mottled leaves and small, warty fruit. Infected hostas show mottled, puckered leaves; hellebores with black death develop black streaks and net patterns. Similar mottling can be caused by nutrient shortage, herbicide drift or sap-sucking pests, so check for those first.
Cause
Viruses cannot travel on their own. Aphids carry many of the commonest ones, while whitefly, thrips, some soil nematodes and fungi spread others. Viruses also move in sap on hands, knives and secateurs, and in infected seed, tubers, bulbs, runners and cuttings. Weeds and older ornamentals can act as reservoirs.
Control
No spray cures a virus. Remove infected plants as soon as you are sure, including the roots, and put them in household waste. Do not propagate from them. Wash hands and wipe blades with disinfectant after handling suspect plants. Deal with aphids early by squashing them or hosing them off.
Prevention
Buy certified seed potatoes and virus-free strawberry and raspberry plants, and replace soft fruit beds every few years. Choose resistant varieties, such as courgette 'Defender'. Keep weeds down, encourage ladybirds and other aphid predators, and avoid dividing any plant that has ever shown symptoms.
Plants often affected
Could it be something else?
These problems share some of the same symptoms. Compare them, or run the symptom checker with these signs ticked.
Months to keep an eye out: April, May, June, July, August, September and October.
Sources
Identification and life-cycle details were checked against the references below. Text and advice are our own. See our editorial policy.