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.
| 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.