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Cucumber mosaic virus causes foliage to be distorted with a mottling of light and dark green.

Tomato

Mosaic Virus Diseases Caused by Cucumoviruses

Pathogen: Cucumber mosaic virus in the cucumovirus group

(Reviewed 1/08, updated 1/08)

In this Guideline:


SYMPTOMS AND SIGNS

Symptoms on plants infected with cucumoviruses can vary. Generally, plants appear lighter in color and are bushy and stunted. Close up symptoms include a mosaic (alternating light and dark green areas) on at least some leaves, especially on the younger leaves. Leaves may exhibit a shoestringlike appearance. Fruit production is greatly reduced. These symptoms can be confused with those caused by tobacco mosaic virus.

COMMENTS ON THE DISEASES

Cucumber mosaic virus is spread from plant-to-plant by many species of aphids. Aphids only retain the ability to transmit these viruses for very short periods of time (minutes to a few hours). Thus, spread is often very rapid and local. In general, field spread of Cucumber mosaic virus occurs when aphid activity in fields is high. The type of aphid activity that promotes virus spread occurs when aphids actively move through the crop, not when they colonize plants. There are many strains of cucumber mosaic and it has a very wide host range among dicot crop and weed species. Thus eliminating alternate sources of inoculum is not a feasible management strategy.

MANAGEMENT

Because outbreaks of virus diseases are unpredictable from year to year and for various geographic locations, the control of these diseases is difficult and not usually practiced.

The use of silver reflective mulches may delay the infection by aphid-borne viruses and reduces the incidence and severity of these diseases by repelling aphids that transmit them. Place reflective polyethylene mulches on planting beds before seeding or transplanting to reduce aphid landing and virus transmission. The mulches lose their effectiveness when more than 60% of the surface is covered by tomato plant foliage.

No good sources of cucumber mosaic resistance in tomatoes are currently available. Efforts are underway to develop resistant cultivars, both through traditional plant breeding and biotechnological approaches. No effective chemical pesticide strategies are effective. Insecticides directed at controlling the aphid vectors are ineffective because they cannot kill the aphids before transmission occurs.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Tomato
UC ANR Publication 3470
Diseases
R. M. Davis, Plant Pathology, UC Davis
G. Miyao, UC Cooperative Extension, Solano/Yolo counties
K. Subbarao, USDA Agricultural Research Station, Salinas
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgments for contributions to the disease section:
B. W. Falk, Plant Pathology, UC Davis

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