How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms on plants affected by mosaic diseases can vary. In general, plants develop an overall lighter coloring and a bushy appearance. Close up symptoms include a mosaic (alternating light and dark green areas) on some leaves, especially the younger ones. Leaves may also be curled. Fruit may be distorted and develop mosaic symptoms. Internally, brown areas and necrotic areas develop and the fruit do not ripen normally.

COMMENTS ON THE DISEASES

The tomato potyviruses are transmitted 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 localized. In general, spread of tomato potyviruses in the field 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. The tomato potyviruses have wide host ranges, including other crops and many weed species, particularly within the plant family Solanaceae. Various strains of the tomato potyviruses exist, some of which differ in their specific pathogenicities. It is common to find plants simultaneously infected by more than one of the tomato potyviruses, and to also be infected by cucumber mosaic virus.

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. Insecticides do not effectively control these viruses because they do not kill the aphids before they can transmit the viruses.

PUBLICATION

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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