Mosaic Disases

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

Cucumber mosaic (Public Domain)

---

Mosaic diseases are caused by a variety of viruses that can infect the majority of your garden plants. Since these diseases are difficult or impossible to treat, recognizing and removing infected plants right away can help prevent the disease from spreading.


Symptoms of mosaic diseases

The classic mottled appearance of infected leaves is only one symptom of mosaic disease. Leaf cupping, blistering, stunting, crinkling, and other distortions are also common symptoms of mosaic disease. Stems may be shortened, creating a bushy appearance to vines. 


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, while future growth is distorted. Fruit may also show the same mottling and other distortions seen on leaves. Warty bumps are common.

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

---

Plants that host mosaic diseases

It would be easier to list plants that are not affected by mosaic disease. Plants commonly infected with mosaic diseases include:

• apples 
• bananas
• beets
• blueberries
• cabbage family - cauliflower, parsnips, radishes, turnips
• celery
• cereals - barley, oats, rye, and wheat
• chayote
• cucurbits - cucumbers, melons, squash, zucchini
• endive
• figs
• grapes
• hops
• legumes - beans, cowpeas, peanuts, peas, soybeans
• lettuce
• mulberries
• nightshade family - eggplant, peppers, potatoes, tomatoes
• okra
• olives
• onions and scallions
• papaya 
• passionfruit 
• peaches
• sunflowers

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

---

Common mosaic diseases

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

• bean common mosaic
• bean mosaic
• bean yellow mosaic
• cucumber mosaic
• fig mosaic
• pea seedborne mosaic
• squash mosaic
• tobacco mosaic
• watermelon mosaic
• zucchini yellow mosaic

Mosaic disease management

Generally speaking, mosaic diseases are not curable. Infected plants should be removed. This means that prevention is a far better course of action. 


Depending on the specific virus, it may be carried in to your garden on seeds or tools, or by aphids, dryberry mites, and any number of other sap-sucking pests. Removing weeds that could provide overwintering sites, creating physical barriers with row covers and walls of non-host plants, and regularly sanitizing your tools goes a long way toward preventing mosaic disease from taking hold in your garden, as does buying clean, disease-resistant seeds and plants from reputable suppliers.


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.