Mosaic viruses
Also known as Cucumber mosaic virus (CMV), Tobacco mosaic virus (TMV), Plant viruses
In short
Mosaic viruses are a mixed group of plant viruses named for the patchy light- and dark-green mottling they cause on leaves. They are not one family: cucumber mosaic virus and tobacco mosaic virus, for example, are unrelated. There is no cure, so infected plants are removed and the spread is stopped.
How it looks
Leaves show an irregular mosaic or mottle of light green, yellow and dark green patches. Other common symptoms are ring-shaped spots or line patterns, puckered, blistered or wavy-edged leaves, curling or narrowing of leaves, stunting, fewer flowers and streaks or colour-breaking in flowers. Some viruses cause dead (necrotic) spots, streaks and rings on leaves and stems. Symptoms are often strongest on new growth and can be mild or absent on some plants that still carry the virus.
Signs
Mottled or streaked leaves; distorted, puckered or narrow new leaves; stunted growth; poor flowering and abnormal flower colour; ring spots or necrotic lines.
Life cycle
Viruses live and multiply only inside living cells. Cucumber mosaic virus is carried mainly by aphids and also by hands; tobacco mosaic virus is not spread by insects but moves very easily on hands, tools and clothing when people handle infected and then healthy plants. Some viruses spread through seed, thrips (impatiens necrotic spot virus) or soil nematodes (ringspot viruses). Weeds can act as reservoirs.
What favours it
Spread is favoured by aphid or thrips infestations, weeds near plants, taking cuttings or divisions from infected plants, and handling many plants in a row without washing hands or cleaning tools.
Prevention
- Inspect new plants for mottled or distorted growth and quarantine them before they join the collection.
- Control aphids and thrips early, and remove weeds around growing areas.
- Wash hands and clean tools between plants, especially when pruning or taking cuttings.
- Never propagate from plants with suspicious mottling.
- Where available, choose virus-resistant varieties.
Treatment
Start with the first step and move down only if the problem persists.
- There is no cure: remove and bin infected plants (do not compost), including roots.
- Wash hands and disinfect tools and benches after handling infected material.
- Control insect vectors on the remaining plants, starting with cultural and biological options.
- Watch neighbouring plants for new symptoms for several weeks.
Pros and cons
Cons
- Incurable and permanent in the infected plant.
- Easily spread by hands, tools and insects.
- Symptoms can be mild or hidden, so infected plants may go unnoticed.
Look-alikes
- Nutrient deficiency
- Deficiency chlorosis follows a regular pattern (older or newer leaves, between the veins) and fertilising improves new growth; viral mottling is irregular and does not respond to feeding.
- Spider mite damage
- Mites cause fine pale speckling with webbing and mites visible on the leaf underside.
- Thrips damage
- Thrips leave silvery scarring and black specks of droppings rather than a green-yellow mosaic.
- Natural variegation
- Variegation is stable, regular for the cultivar and does not distort leaves.
Affected plants
Tobacco mosaic virus has been recorded in more than 150 plant genera, including petunia, cyclamen, gerbera, New Guinea impatiens and geranium; cucumber mosaic virus has a very broad host range of vegetables, perennials, woody ornamentals and weeds.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.