Abstract:
Contact and systemic insecticides formulated as emulsive concentrates (EC), wettable powders (WP), and granules (G) were compared at various times, rates and intervals of application to control the six-spotted leafhopper, Macrosteles fascifrons (Stal), and prevent the spread of aster yellows virus (AYV) to head lettuce and carrots. The insecticides malathion EC, Baygon EC and G and phorate G, at the rate of one pound per acre controlled the six-spotted leafhopper and prevented the spread of AYV to the head lettuce in the spring and summer crops of 1960, 1961 and 1962. The same insecticides gave only partial protection to the spring crop and failed to protect the summer crop of 1963 because of a combination of a large population of M. fascifrons with a high percentage (ten per cent) of infective leafhoppers. Other insecticides tested against M. fascifrons on head lettuce were less effective... Three strains of AYV, "A", "B", and "C", were isolated from lettuce, zinnia and celery, respectively, in Manitoba... The transmission of the three strains of AYV by single infective M. fascifrons showed that the six-spotted leafhopper, male or female, is a consistent and reliable transmitter after a two-day inoculation feed; that aster is a poor indicator of the proportion of infective leafhoppers; that stinkweed and head lettuce are superior indicator plants; and that different species of host plants vary in their susceptibility to different strains. The acquisition of the three strains of AYV by M. fascifrons from 14 different host plants showed that it depended on the strain of AYV and the host plant.
