Weed species present on the floor of three commercial peach orchards and in deep irrigation drainage ditches in the Yakima Valley of Washington were screened in the springs of 1978 and 1979 to determine which species hosted viruliferous green peach aphid (GPA),Myzus persicae(Sulzer), a vector of beet western yellows virus (BWYV). Twenty-three weed species (>2,700 individual plants) were found to host GPA. Disease readings of indicator plants after feeding by field-collected GPA from 15 weed species showed that infestation rates of GPA ranged from 1.4 to 33%, equivalent to 523,957 BWYV vectors per ha in the peach orchards. Peach trees were determined to be nonhosts of BWYV.