Introduction
Pyrethrum (Tanacetum cinerariifolium) is grown for the production of natural insecticidal pyrethrins
produced in the achenes within the flowers. Natural pyrethrins possess properties of low
mammalian toxicity and rapid environmental degradation, making them ideally suited for insect
control in domestic and industrial situations. Approximately 3000 ha of pyrethrum are grown in
northern Tasmania and Ballarat in Victoria for Botanical Resources Australia Pty. Ltd. (BRA). The
Australian industry has bred high pyrethrin content varieties with synchronous flowering suited for
mechanised harvest, coupled with intensive methods of growing, and sophisticated methods of
harvesting and extracting. The Australian industry has grown rapidly in the last few years, and now
supplies some 60% of the global market for natural pyrethrins.
TIA supports the pyrethrum industry with projects investigating (i) Ray blight disease
(Stagonosporopsis tanaceti) and Tan spot disease (Microsphaeropsis tanaceti), (ii) Crown rot and
flower blights caused by Sclerotinia sclerotiorum and S. minor and, (iii) frost and salinity tolerance
Ray blight and Tan spot diseases
In year 2000, the industry was devastated by an outbreak of an unknown disease. The disease
caused complete crop loss in many instances. Investigations by Drs Pethybridge and Hay (TIA)
identified the disease as ray blight caused by the fungus Stagonosporopsis tanaceti (syn. Phoma
ligulicola). Research in collaboration with BRA has provided much information on the aetiology and
epidemiology of the disease, site risk, population genetics of the pathogen and methods of control.
A fungicide program was developed and has been employed by over 95% of growers annually.
Demonstration trials in over 100 fields have indicated net average benefits of over $3500/ha over
and above the cost of fungicides (Pethybridge et al. 2008).
A new disease of pyrethrum (Tan spot) was recently described and attributed to a newly described
fungus (Microsphaeropsis tanaceti) (Pethybridge et al. 2008). Recently M. tanaceti has been
associated with severe disease in some crops. M. tanaceti has been shown to have developed
insensitivity to one of the commonly used fungicides in spring, and recent changes have been made
to the program to accommodate this. M. tanaceti is the subject of current studies into epidemiology,
steam sterilisation of seed, fungicide sensitivity and population genetics by Drs. Frank Hay and Jason
Scott and Ph.D student Tamieka Pearce. This work is supported through Horticulture Australia Ltd.
Project PY12001, with funding from the Commonwealth Govt., Botanical Resources Australia Pty. Ltd.
and the Tasmanian Institute of Agriculture and Cutherbertson Elite Tasmanian Graduate Research
Scholarship.
Diseases caused by Sclerotinia spp.
Sclerotinia sclerotiorum and S. minor are the cause of crown rot of plants and flower blight. These
fungi persist as seed-like sclerotia, which are aggregates of melanised fungal mycelium. In autumn,
winter and spring each year, a proportion of sclerotia germinate to produce mycelium that infects
the base of the plant or the leaves contacting the ground. Fungi grow through the plant causing
rotting and wilting, and form characteristic white cottony mycelium and new sclerotia. Plants may
die or may recover in drier conditions. The disease is favoured by high plant density and canopy
cover and wet conditions. In summer, sclerotia germinate carpogenically to produce mushroom-like
structures (apothecia) from which airborne spores (ascospores) are produced. Ascospores infect
flowers and cause flower blights. Pyrethrum is one of the rare cases in which carpogenic germination
of sclerotia of S. minor have been shown to play a role in disease. TIA researchers Dr. Jason Scott and
Frank Hay are investigating the effect of disease on crop persistence, fungicidal control and the
identification of site specific risk factors predisposing crops to disease through an ARC Linkage grant
supported by Botanical Resources Australia Pty. Ltd.
Frost and salinity tolerance
Mark Boersma to provide information.