Mosaic Disases

Speckled, mottled, or otherwise deformed leaves and fruit usually indicate a mosaic disease.

Cucumber mosaic (Public Domain)

Mosaic diseases are a collection of viral infections that can infect most of your garden plants. Since these diseases are difficult or impossible to treat, recognizing and removing infected plants as soon as possible can help prevent the disease from spreading.

Symptoms of mosaic diseases

The classic mottled appearance of infected leaves is only one symptom of a mosaic disease. Leaf cupping, blistering, stunting, crinkling, and other distortions are other common symptoms of mosaic diseases. Stems may also be shorter, creating a bushy appearance to vines. Fruit may also show the same mottling and other distortions seen on leaves. Warty bumps are also commonly seen.

Plants infected early in the growing season rarely produce fruit. Interestingly, plants infected later in the season retain their healthy, earlier growth and fruit production. Distortions only occur in post-infection leaves and fruit.

Turnip yellow mosaic virus on cabbage (Michal Maňas) CC BY 2.5

French bean infected with bean common mosaic (ShoutWiki) CC BY-SA 3.0

Plants that host mosaic diseases

It would be easier to list plants that are not affected by mosaics. But the plants most commonly infected with mosaic diseases include the following:​

• Apples 
• Bananas
• Beets
• Blueberries
• Cruciferous - cauliflower, parsnips, turnips
• Celery
• Cereals - barley, oats, rye, and wheat
• Chayote
• Cucurbits - cucumbers, melons, squash, zucchini
• Endive
• Figs​
• Grapes

• Hops
• Legumes - beans, cowpeas, peanuts, etc.
• Lettuce
• Mulberries
• Nightshade - eggplant, peppers, tomatoes
• Okra
• Olives
• Onions and scallions
• Papaya 
• Passionfruit 
• Peaches
• Sunflowers

Common mosaic diseases

While there are dozens (hundreds?) of mosaic diseases, some of the more common varieties include this list:

• Bean common mosaic

• Bean mosaic
• Bean yellow mosaic
• Cucumber mosaic
• Fig mosaic​

• Pea seed-borne mosaic
• Squash mosaic
• Tobacco mosaic
• Watermelon mosaic
• Zucchini yellow mosaic

Mosaic disease management

Generally speaking, mosaic diseases are not curable. Remove infected plants and toss them in the garbage. Prevention is a far better course of action. 

Depending on the specific virus, it may catch a ride into your garden on seeds, tools, aphids, dryberry mites, and other sap-sucking pests. These tips can help reduce the chance of a mosaic disease robbing you of your harvest:

• Buy clean, disease-resistant seeds and plants from reputable suppliers.
• Remove weeds that could provide overwintering sites.
• Create physical barriers with row covers and walls of non-host plants
• Sanitize your tools regularly with a household cleaner.

While mosaic diseases make plants look funny, the fruit of infected plants is still safe to eat. The viruses responsible for mosaic diseases are not harmful to people.