Epidemiology and strategy for the control of halo‐blight of beans

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Abstract
SUMMARY: A halo‐blight epidemic model based on the equation of Van der Plank (1963) is described. The model has been used to determine tolerance levels for seed infection and to compare the effectiveness of chemical control measures based on foliar sprays and seed treatments.Reduction of primary inoculum, derived from infected seed, by disease exclusion through seed testing, or by chemical seed treatment will give effective disease control under British conditions (i.e. with an expected apparent infection rate (r) of 0.15 per infected plant per day). Under climatic conditions more favourable for the disease where higher r values would occur, control treatments directed against primary inoculum only would be less effective. Under such conditions, it is predicted that chemical sprays, which have no effect on primary inoculum but cause a reduction in the rate of disease increase, would be more effective. The most effective disease control, however, would be a combination of treatments.