Influence of Phoma ligulicola on yield, and site factors on disease development, in Tasmanian pyrethrum crops

Phoma ligulicola Boerema was isolated from diseased buds, and necrotic stem and leaf lesions in 24 pyrethrum fields approaching their first harvest in northern Tasmania. Despite the ubiquitous distribution of this pathogen, m arked differences in disease severity were evident in several fields. A hig her incidence of disease was noted in fields with a southerly exposure and low areas within fields than on sites with a northerly exposure and hill cr ests. In 52% of the fields surveyed, P. ligulicola was associated with redu ced yields of pyrethrin (kg ha(-1) active ingredient) of up to 100%.