It occurs anywhere lettuce is grown, causing bitter, stunted and disfigured heads. The young heart leaves become white to yellow and fail to develop normally remaining as short, thickened stubs in the middle of the head. Light brown to pink latex spots collect on the undersides of the midribs of the leaves. When young plants are infected, outer leaves become yellow and twisted. These plants may be severely stunted.
Heads often taste bitter.
Bushy outgrowths may be present on the flowering stalks, and the plants may be sterile or abort seeds. The adults must feed on an infected plant for about eight hours before they acquire enough of the phytoplasmas to infect a healthy plant. After the leafhopper has acquired the phytoplasma, it is able to transmit it to healthy plants for the rest of its life. T his is the most important way this disease starts in an area. The insect that spreads the disease may spend the winter on wheat, rye, barley and some grasses.