How to Manage Pests

UC Pest Management Guidelines


Alfalfa Mosaic

Pathogen: Alfalfa mosaic virus (AMV)

(Reviewed 12/09, updated 12/09)

In this Guideline:


Typical symptoms of pepper plants infected with alfalfa mosaic virus are a distinct yellow or whitish mosaic on leaves. Relative to uninfected plants, fruit may be stunted and misshapen.


Alfalfa mosaic virus infections of peppers more commonly occur when peppers are grown near alfalfa fields. Alfalfa mosaic virus is seedborne in alfalfa and essentially all alfalfa fields can be considered infected. Alfalfa mosaic virus is transmitted by several species of aphids and spread from alfalfa to surrounding crops via aphids is common. Aphids transmit the virus only while probing the leaf tissues. Once an aphid acquires alfalfa mosaic virus, it retains the ability to transmit the virus for only a short period of time (minutes to hours) and spread is local and can be very rapid within fields. In general, field spread is related to overall aphid activity, not to the presence of colonizing aphids. Except in fields near alfalfa, the disease is usually not economically important.

Alfalfa mosaic virus is the only virus in the alfamovirus group and has a wide host range among weed and crop plants.


In general, alfalfa mosaic virus is not a major problem in California peppers, although local alfalfa mosaic virus infections occur each year. The best way to control alfalfa mosaic virus is to avoid planting peppers near alfalfa fields. No resistance is currently available in commercial pepper cultivars. Insecticides aimed at controlling the aphid vectors are largely ineffective. They will not kill aphids before aphids transmit the virus to plants.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Peppers
UC ANR Publication 3460


S. T. Koike, UC Cooperative Extension, Monterey County
R. M. Davis, Plant Pathology, UC Davis
K. V. Subbarao, USDA Research Station, Salinas

Acknowledgment for contributions to Diseases:
B. W. Falk, Plant Pathology, UC Davis

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