Cucumber Mosaic Virus (CMV)

Problem type: Disease

Name of problem: Cucumber mosaic virus (CMV)

Plant name(s): Cucumber, muskmelon, pumpkin, squash, watermelon, zucchini, lettuce, spinach, pepper, tomato, rhubarb, celery, corn, and bean

Symptoms / Characteristics:
Tiny, yellowish lesions form on young leaves. As the disease progresses, the leaves become mottled, wrinkled, curled and deformed. Overall plant growth is stunted. Older leaves may exhibit V-shaped necrotic lesions pointing inward, towards the leaf center. Infected fruit is also mottled, beginning at the stem, with dark green wart-like bumps. Symptomatic cucurbit fruits (e.g. cucumber, melon, squash etc.) often exhibit a condition termed white pickle, whereby the skin is smooth and whitish with green blotches. These fruits are typically deformed. Symptoms of the virus are slightly different in tomato and pepper. Young tomato leaves become extremely narrow, giving them a "shoestring" appearance. In pepper, rings of dead tissue will form on the leaves. The immature fruit of infected pepper plants may exhibit a similar yellow-ringed pattern. Plants infected with CMV generally tend to produce few fruit.

CMV can infect both greenhouse and field-grown vegetable crops and has also been known to infect several ornamental flowers, including gladiolus, impatiens and petunia. Many weed species act as alternative hosts, enabling the virus to persist from year to year. Several sap-sucking insect vectors, namely aphids and cucumber beetles, facilitate viral transmission to healthy hosts. Striped cucumber beetles are yellow with a black head and three black stripes running down the folded wings. Spotted cucumber beetles have a yellowish-green body with a dozen large, black spots on the folded wings. They may reach a mature length of approximately 7mm, whereas the striped beetles may only reach a length of 5-6mm. Feeding commences in late spring/early summer when seedlings have begun to emerge and transplants are moved into the vegetable garden

Control / Preventions:
Begin monitoring for aphids and cucumber beetles in the spring, just after seedling emergence or after transplants have been moved into the garden. Check both vegetable plants and neighbouring weeds for signs of insects and feeding damage. Significant insect populations and/or damage may warrant the use of an insecticide. Controlling the insect vectors as soon after emergence as possible is an effective way to prevent transmission of the cucumber mosaic virus. Remove from the growing area all weed and ornamental species that may serve as alternative hosts for the virus. Perennial weed control is essential, as the weeds can harbor both the virus and the insect vectors. The virus is systemic; once a plant becomes infected it cannot be cured. Immediately remove and destroy symptomatic plants in order to prevent further transfer to healthy hosts. Removal of symptomatic leaves, stems and fruits will not eliminate the virus from otherwise healthy looking plants and may only lead to further spread via infested tools, etc. While pulling diseased plants from the field or garden, avoid any contact with healthy plants. Thoroughly disinfect tools and equipment that may have come in contact with the diseased plants. Sap on infested tools and plant parts can be an ideal way to transmit the virus from one plant to another. Resistant varieties may be available, depending on the vegetable/ornamental plant species in question.