Virus diseases

also called Mosaic virus, Plant viruses

Mottled, streaked, or distorted growth that never recovers; spread by sap-suckers and tools. Destroy affected plants, control aphids, and keep tools clean.

Virus No cure Spread by insectsSpread on tools & handsSpread by contact Spreads to neighbors

What you'll see

Irregular light and dark green mosaic mottling on the leaf that follows no vein pattern and does not rub off.
Yellow rings, streaks, arcs or vein-clearing that appear on new growth as it unfurls.
Leaves are puckered, narrow, strap-like or fern-like, and shoots may be stunted and bunched.
Flowers are streaked or broken in color, and fruit is mottled, lumpy or fails to set.
Only some plants in a row are affected, and no fungus, insect or lesion can be found to explain it.

Why it happens

Viruses are packets of genetic material that replicate inside plant cells and cannot be cured or sprayed out. They are carried by sap-sucking insects — chiefly aphids, whitefly and thrips — by eelworms in the soil, on secateurs and hands, in cuttings and tubers, and sometimes in seed. Once a plant is infected, it is infected for life and becomes a reservoir for everything nearby.

Outbreaks follow high aphid and whitefly numbers, so a warm dry spring and a mild winter both make a bad virus year. Propagating from your own stock over many years, and handling plants after smoking or after touching an infected plant, both keep it circulating.

Treating it

There is no treatment. Lift affected plants promptly, bag them and bin or burn them.
Wash hands and sterilize secateurs, knives and dibbers with alcohol or a disinfectant before touching another plant.
Control aphids, whitefly and thrips, since they are the means of spread rather than a coincidence.
Do not save seed, take cuttings or divide from an affected plant.
Keep the remaining plants growing well; a vigorous plant tolerates a mild infection longer, though it does not clear it.

Keeping it away

Buy certified virus-free stock for raspberries, strawberries, potatoes and fruit trees.
Grow resistant cultivars where they exist, particularly for cucumber and tomato mosaic.
Keep on top of aphids and whitefly early, before populations build.
Weed thoroughly — chickweed, groundsel and sowthistle harbor several common viruses over winter.
Clean tools between plants when taking cuttings, budding or pruning.

Who gets it

Tomatoes, cucumbers and courgettes, peppers, raspberries, strawberries, dahlias, lilies and tulips are among the most frequently affected.