Those striking green-and-yellow marbled leaves hanging over the fence from your neighbor’s apple tree may look like a fashionable new cultivar, but they are more likely the result of a mosaic virus.
What Are Mosaic Viruses?
- Mosaic viruses are among the most common plant viruses worldwide
- Over 2,000 plant viruses are known; many cause serious disease
- They are submicroscopic, non-cellular particles that infect living plant cells
- Once inside, they hijack the plant’s cellular machinery, disrupting normal growth
- “Mosaic” symptoms can be caused by different viruses or virus complexes, not just one pathogen
Plants Commonly Affected
- Food crops – Alfalfa, apples, beans, celery, corn, cucumbers, figs, peppers, spinach, tobacco, tomatoes
- Ornamentals – Abutilon, delphinium, gladiola, marigold, petunia, and roses (rose mosaic virus complex)
Typical Symptoms (vary with plant species, virus type, and weather)
- Yellow-and-green mottling or mosaic patterns on leaves
- Puckered or distorted foliage
- Vein clearing or banding
- Patterns may appear attractive but indicate infection
- In California, symptoms usually appear in cool spring weather and fade in summer heat
- Crop yield and vigor may be reduced 25–50%
How Mosaic Viruses Spread
- Transmitted mainly by sap-feeding insects, especially aphids
- Spread rapidly but locally through contaminated tools or hands, and seeds, pollen, and vegetative propagation
- Rose mosaic spreads primarily through grafting or cuttings, not insects
Management and Prevention
- There is no cure once a plant is infected
- Focus on maintaining good plant care and vigor, managing insect vectors with non-chemical methods and purchasing certified virus-free plants
Back to the Apple Tree
All apple varieties are susceptible to apple mosaic, particularly ‘Jonathan,’ ‘Golden Delicious,’ and ‘Granny Smith.’ While the tree usually survives, fruit production is often reduced.