How to Manage Pests
UC Pest Management Guidelines
Symptoms of aster yellows on lettuce include blanching and chlorosis of the young heart leaves. The center leaves fail to develop normally and remain as short, thickened stubs in the middle of the head. Outer leaves become yellow and twisted. Pink to tan latex deposits collect on the underside of midribs of affected leaves. If young plants are infected, outer leaves yellow and the plants may be severely stunted. If older plants are infected, latex spots in the interior of the head may be the only symptoms.
The aster yellows phytoplasma (formerly known as mycoplasmalike organisms) overwinters in the body of adult leafhoppers and in perennial or biennial host plants, including native plants, ornamentals, and weeds such as Russian thistle (Salsola tragus), sowthistle (Sonchus spp.), prickly lettuce (Lactuca serriola), dandelion (Taraxacum offinale), and many others. The principal vector is the aster leafhopper, Macrosteles quadrilineatus, although the phytoplasma can be transmitted by many other species of leafhoppers. Leafhoppers can remain inoculative for at least 100 days. In some areas, the occurrence of aster yellows may follow the pattern of leafhopper migration.
Control includes removal of weed reservoirs near lettuce fields, control of vectors with insecticides, and planting away from earlier lettuce plantings that contain diseased plants. However, control measures are not usually warranted. There are no resistant or immune lettuce varieties.
UC IPM Pest Management Guidelines: Lettuce