Host-Free Districts and Periods

The Agricultural Commissioner, in collaboration with CDFA, enforces host-free periods as a critical step to break disease life cycles or prevent disease establishment. Host-free periods are in effect for the following commodities being growing in Monterey County:

Host Plants: Lettuce (Lactuca spp.), Endive & Escarole (Chichorium endive) 
Pest/Disease: Lettuce Mosaic Virus 
No Plant Period: December 7-21 each year 
Host-free District: County of Monterey

No host plant shall be grown above ground during the host-free period except under permit. Leaves of plants that are infected with lettuce mosaic virus at a young stage are stunted, deformed, and (in some varieties) show a mosaic or mottling pattern. An infected seed is a primary way of introducing lettuce mosaic to fields. The virus can infect numerous crops and weeds, thereby creating reservoirs of the virus. Lettuce mosaic virus can also be vectored by aphids, which spread the virus within a lettuce field and introduce it into lettuce fields from infected weeds and crops outside the field.

Host Plants: Celery (Apium graveolens) 
Pest/Disease: Western Celery Mosaic Virus 
No Plant Period: January each year 
Host-free District: County of Monterey

No host plant shall be grown above ground during the host-free period except under permit. Plants infected at an early age are greatly stunted, and the foliage, after showing early mosaic, becomes cupped and malformed. The virus is transmitted by several aphid species and is limited only to umbelliferous plants (celery, carrot, parsley, etc.). Because of the limited host range, destruction of umbelliferous weeds is a recommended control measure.

Host Plants: Lombardy Poplar Tree (Populus nigra) 
Pest/Disease: Lettuce Root Aphid 
No Plant Period: At any time
Host-free District: Salinas Valley & portions of Pajaro Valley
View the static PDF map or interactive map viewer.

No Lombardy poplar may be grown or maintained at any time in the district except under a permit. Permits will require pesticide treatments to control the pest on the host.

To request a permit for any of the above, please call Agricultural Programs Biologist Hannah Wallis at (831) 759-7332.

Regulatory Disease Control Programs

Lettuce Mosaic Virus Disease Control Program

Lettuce Mosaic Virus (LMV) is a seed borne disease. No lettuce seed may be planted in the County of Monterey unless it has been “indexed” or tested and found to have no more than zero virus in 30,000 seeds. There is an exemption for planting for home gardens. A permit to use non- mosaic indexed seed may be issued by the Agricultural Commissioner if the necessary indexed seed of a particular variety is not available.

The Agricultural Commissioner operates the LMV seed mosaic indexing program in cooperation with the Grower Shipper Association of Central California (GSA). To submit seed for testing call the GSA at (831) 422-8844.