Epidemiological factors influencing the success of roguing for the control of bunchy top disease of bananas in New South Wales

Abstract

An infection chain was reconstructed from historical data of a typical outbreak of bunchy top disease of bananas to determine factors influencing the seasonal occurrence and eradication of disease under roguing. The results were described by a mathematical model involving four random variables (incubation period, relative infection rate, detection efficiency and eradication efficiency) and one fixed variable (inspection interval). The model successfully predicted the course of roguing in an independent disease outbreak. The incubation period of the disease depended on the time taken for two banana leaves to emerge after inoculation. At Alstonville, N.S.W., the incubation period varied from 19 days in summer to 125 days in winter. The relative infection rate varied on average from 0.027 to 0.001 new infections per old infection per day in summer and winter respectively. Efficiency of disease detection by experienced inspectors depended on the number of leaves displaying disease symptoms and, equally, on time of year. Under the normal 3-weekly inspection routine, detection efficiency varied from 0.94 in summer to 0.19 in winter, plants being found on average at the two-leaf stage of disease. The efficiency with which banana growers eradicated diseased plants following their detection was found to be a characteristic of the grower concerned but was, in general, poorest in late summer.