Reducing the immigration of suspected leafhopper vectors and severity of Australian lucerne yellows disease

Abstract

Three newly-sown lucerne stands in the mid Lachlan Valley region of New South Wales, Australia, were sampled, over 50 weeks, for Australian lucerne yellows disease symptom distribution and severity. Leafhopper populations were also monitored. Symptoms developed in all 3 stands within 32 weeks of sowing. There were statistically significant spatial differences in the density of symptomatic plants for 2 dates at this and another site. Two possible insect vectors, Austroagallia torrida and Batracomorphus angustatus were more numerous in some sections of crop margins at 2 sites. These 2 species and a third possible insect vector Orosius argentatus each had a statistically significant spatial and temporal correlation with symptomatic plant numbers for at least 1 site date. Two subsequent border treatment experiments evaluated the effect of crop-margin treatments on leafhopper movement into and from the stand. The second border treatment experiment examined also the treatment effect on Australian lucerne yellows disease symptomatic plant numbers. Treatment with insecticide or herbicide significantly reduced the overall movement of leafhoppers. In addition, the insecticide treatment lowered the incidence of disease expression in adjacent lucerne. Results suggest that there is scope for management of this plant disease by reducing immigration of leafhopper vectors into lucerne from non-crop vegetation.