Agriculture: Lettuce Pest Management Guidelines

Beet Western Yellows

  • Beet western yellows virus
  • Symptoms and Signs

    On lettuce, symptoms of beet western yellows rarely develop until plants reach rosette stage. At this point in crop development, the older leaves begin to turn yellow. This yellowing continues until all the oldest, lower leaves are bright yellow, or (less frequently) almost white, with the main leaf veins remaining green. Yellowed leaves often have a thick, brittle texture. Yellowing can progress until the wrapper leaves adjacent to the head also turn yellow, and head color may be unacceptably light green. In most lettuce varieties, significant stunting or reduction in plant size does not occur. Overall symptoms of this yellows disease may resemble nutrient deficiencies, such as iron chlorosis. This distinctive yellowing of older leaves sets this disease apart from other lettuce virus diseases.

    Comments on the Disease

    The disease is caused by Beet western yellows virus, which has an extensive host range, including over 150 documented plant species (see list below). Isolates or strains of this virus vary in their ability to infect different plant species; thus, not all strains of Beet western yellows virus may be able to infect all plant species, greatly complicating the study of this disease.

    Beet western yellows virus is vectored by several aphid vectors, especially the green peach aphid. The virus is transmitted in a persistent manner by the aphid, meaning that once the aphid has acquired the virus by feeding on infected plants, that aphid can essentially continue to transmit the virus for the rest of its life. Unlike Lettuce mosaic virus, Beet western yellows virus is not seedborne in lettuce.

    Partial List of Potential Host Reservoirs for Beet western yellows virus.
    Host Agronomic Plants
    Common Name Scientific Name
    beet, sugarbeet Beta vulgaris
    bell pepper Capsicum annuum
    black mustard Brassica nigra
    broccoli Brassica oleracea ssp. botrytis
    cabbage Brassica oleracea ssp. capitata
    cauliflower Brassica oleracea ssp. botrytis
    chickpea/garbanzo bean Cicer arietinum
    endive Cichorium endivia
    escarole Cichorium endivia
    fava bean Vicia faba
    lettuce Lactuca sativa
    mustard/rape Brassica napus
    pea Pisum sativum
    phlox, annual Phlox drummondii
    radish Raphanus sativus
    spinach Spinacia oleracea
    spinach, New Zealand Tetragonia expansa
    subterranean clover Trifolium subterraneum
    sunflower Helianthus annuus
    tomato Lycopersicon esculentum
    turnip Brassica rapa
    zinnia Zinnia elegans

    Host Weeds
    Common Name Scientific Name
    blite, strawberry Chenopodium capitatum
    chickweed, common Stellaria media
    groundsel, common Senecio vulgaris
    lettuce, prickly Lactuca serriola
    mallow, little (Cheeseweed) Malva parviflora
    saltbush, Australian Atriplex semibaccata
    shepherd's-purse Capsella bursa-pastoris
    sowthistles (Prickly Or Spiny) Sonchus asper

    Management

    In California this virus only occasionally causes significant economic damage. General virus disease management steps, such as those for Lettuce mosaic virus, apply to Beet western yellows virus as well.

    Cultural Control

    Control aphids, although insecticide programs will not prevent transmission of this virus and disease occurrence.

    • Eliminate or reduce virus reservoirs (weeds, volunteer lettuce, and old lettuce fields) with herbicide applications and cultural practices.
    • Consider resistant or tolerant varieties (currently, only few lettuce cultivars are reported to be resistant or tolerant to this virus).

    Organically Acceptable Methods

    Use cultural controls in an organically certified crop.

    Chemical Control

    There are no chemical controls for plant viruses.

    Text Updated: 04/17