Cucumber Mosaic Virus Identification and Treatment

If you’ve noticed a mosaic dark green on your cucumbers or squash, your plants may have contracted cucumber mosaic virus (CMV).

CMV affects a wide array of plants and can’t be cured. But that doesn’t mean you can’t prevent a CMV infection. You have the power to avoid bringing strains into your garden. CMV infects healthy plants, but there are plants with virus resistance. There are also modes of controlling the variables commonly attributed to cucumber mosaic virus. 

What are the host species for cucumber mosaic virus? What do symptoms look like? In this guide, we’ll cover everything you need to know about cucumber mosaic virus.

What Is Cucumber Mosaic Virus?

Cucumber mosaic virus (CMV) is one of the worst viral diseases that can strike a garden. It is transmitted by insects or by mechanical means and overwinters in weeds. It also spreads via infected seeds.

Insects and mechanical vectors can spread CMV incidentally and in a secondary infection. Most vine crops acquire it from secondary infections caused by insects, infected garden tools, and hands that have handled CMV-infested plants and plant debris.

The primary cycle of CMV generally occurs gradually, while the secondary infection is more rapid. 

Life Cycle

Aphid populations (at least 75 different species) are the main culprit for spreading virus particles. As they feed on infected host plants, they pick up the virus within one minute and spread it.

Virus strains penetrate the plant cell. The virus’s coat protein is removed and its viral genome RNA is released into the plant’s cytoplasm. Viral replication occurs in ‘factories’ made of membrane vesicles, spreading the problem.

Cucumber beetles are also a vector of cucumber mosaic viruses. After about 2 minutes, the ability of viral transmission declines significantly. Within two hours it’s almost impossible to spread CMV picked up by an insect who fed on an infected plant. 

The most susceptible plants are young host plants. Because ants tend to harvest honeydew from aphids, they too are one of the main insect vectors of CMV. Controlling these insects in your garden can help you build CMV resistance from the get-go. 

Certain infected weeds can transmit the virus to other plants, especially those that vine around a garden bed via tendrils. For example, pigweed and wild amaranths are hosts for the virus. Keeping weeds out of the garden helps you prevent the spread, too. 

It’s especially important to look out for CMV in environmental conditions where it can proliferate. The virus prefers temperatures between 70°F and 85°F, which typically fall in spring and summer. That’s because these temperatures coincide with the peak of aphid reproductive cycles.

If you want to understand CMV resistance, think about plant stress. Those times that are more stressful for plants are more stressful for CMV. High heat, especially causes a decrease in CMV incidence. Environmental conditions in temperate and tropical climates promote virus replication. Another condition that influences replication occurs when nights are much longer than days. This is when CMV symptoms are more evident. 

Symptoms

While symptoms vary depending on the plant species, a general understanding of the systemic symptoms is necessary. While young plants are most susceptible, it’s not until a few days after infection sets in that symptoms show. Sometimes symptoms take two weeks to manifest.

Early-stage mosaic symptoms on a seedling involve yellowed and wilting cotyledons. Leaves become mottled and look wrinkled. Plant growth is slowed dramatically. 

There are many symptoms infected plants take on when they are experiencing cucumber mosaic virus. In mature plants, leaves take on a yellowish-green to deep-green mottling or mosaic pattern. Vines become bunched in appearance as stem growth between leaves is stunted. Vines are yellow in their centers and fruit production slows.

All the plant parts that grow after an infection become dwarfed, while plant parts that have not been susceptible to infection to that point grow normally. On fruit, look out for the characteristic chlorotic mosaic pattern.

Symptoms by Plant

Cucumbers become excessively warty and soft. They’re often too bitter to enjoy.

More severe symptoms occur on different vegetable crops in different ways. Other cucurbits like musk melon and watermelon take on severe damage in the form of warts as well. Melon warts tend to be lighter in color than cucumber warts.

On pepper plants, a CMV infection looks like stunted growth, mottling on leaves, and dropping foliage. CMV-infected tomato plants become yellow and stunted in the early stages. The most distinct symptom on potato plants is curled leaf ends and a bushy overall appearance.  

CMV affects legumes as well and is often confused with bean common mosaic virus or peanut stunt virus. Characteristically, CMV-infected beans have mottled leaves and a zipperlike roughness along leaf veins. Bean pod production is greatly decreased, and flowers are aborted before they can pollinate. 

Broadleaf plants display typical mottling, leaf-curling, and defoliation. Some develop rings, some have spots, and some develop necrotic lesions shaped like oak leaves. In later stages, grasses will acquire round, yellow-ringed lesions with a dark center.

Susceptible Species

Because CMV affects over 1200 species of plants, we’ve put together a list of some of the most prominent hosts. That way, you can protect plants that are nearby from infections.

This list is extensive, but not complete. Do some cucumber mosaic virus research to determine if a plant species you’re growing has CMV resistance or not. 

Edible Hosts

• Amaranth
• Bananas
• Beets
• Celery plants
• Chard plants
• Cucumbers
• Dill plants
• Eggplants
• Fennel plants
• Green Peppers
• Italian Squashes
• Kava
• Lettuces
• Nasturtiums
• Onions 
• Parsleys
• Parsnips
• Rhubarb plants
• Spinach plants
• Sweet Potatoes
• Tomatoes
• Watercress plants
• Watermelons

Ornamental Plants 

• Aconitum
• Aster
• Astilbe
• Campanula
• Commelina
• Coreopsis
• Datura
• Delphinium
• Echinacea
• Gypsophila
• Helianthus
• Heuchera
• Hosta
• Ligularia
• Lilium
• Lysimachia
• Oenothera
• Penstemon
• Phlox
• Primula
• Scabiosa
• Sedum
• Viola

Weed Hosts

• Bittersweet
• Black Nightshade
• Caltrop
• Common pokeweed
• Crowfoot Grass
• Field Chickweed
• Figwort
• Great mullein
• Mallow
• Marsh yellow cress
• Pigweed
• Plantain
• Primrose
• Purslane
• Sabi Grass
• Smartweed
• Three-nerved Joe Pye
• Wild Gooseberry
• Wood Sorrel

Treatment

Once a species is infected with CMV, you must remove the entire plant and either quarantine it in a sealed plastic bag while you await diagnosis or throw it away. Do not compost affected plants as they could spread the virus to other materials in the pile.

There are no chemicals that treat or cure the disease. With such a wide host range, the best way to control CMV is prevention through cultural methods, seed treatments, and planting virus-resistant varieties. 

Prevention

Through integrated pest management (IPM) practices, you can prevent CMV from getting a foothold in your garden. Control aphids and aphid vectors like ants, and you’re well on your way. Neem oil is a great organic option for aphid infestations in cooler to temperate weather. Spray a diluted commercial formula on your plants as a preventative or to treat aphids. Insecticidal soap is another useful organic method of controlling pesky aphid infestations. 

Lacewings, ladybugs, and birds love to eat aphids. Release them in your garden or encourage them with certain plants and food. You can also remove aphids by hand, or wipe them off plants with a rag dipped in soapy water.

There are cultural practices that assist in preventing CMV. This involves visiting your garden regularly to ensure no disease is present. Remove weeds as they crop up in your garden beds. Eliminate debris that falls onto the soil. 

Because CMV is so prevalent, a lot of research has been done to engineer plants with partial resistance to full resistance. Planting resistant cultivars is a great way to prevent the disease.  

Overfertilization of plants can attract aphid species. So can dry soils. Keep plants well-watered and you’ll prevent the viral protein coat opening associated with CMV.

Because seeds can carry and transfer the disease to a garden, always purchase from reputable sources. If you’ve purchased seeds from a smaller company or have seeds you got from a seed swap or a friend, soak the seeds in a solution of water and 10% bleach solution for 15 minutes in a mason jar. Then rinse the seeds thoroughly with cool water to ready them for planting. 

A hot water seed treatment is also an effective way to prevent CMV. Wrap your seeds in a cheesecloth or a coffee filter. Soak the wrap in water heated to 120°F for 20 to 30 minutes. Then immerse the wrap in cold water for 5 minutes.

Frequently Asked Questions