First report of boeremia blight caused by Boeremia exigua var. exigua on pyrethrum in Australia.
Pyrethrum (Tanacetum cinerariifolium) is produced for extraction of insecticidal compounds from the flower achenes. In 2004 and 2006, isolations from necrotic lesions on stems and leaves in three fields in northern Tasmania, Australia, yielded four unidentified fungal isolates. Leaf lesions were medium brown and circular (2-4 mm in diameter) or irregular in shape (2-5 mm long). Stem lesions were irregular, necrotic spots, 5-15 mm below the flower peduncle, medium brown, 2-4 mm long, and 1-2 mm wide. Based on morphological, cultural, biochemical and molecular characteristics, and pathogenicity tests, the causal agent was identified as B. exigua var. exigua. This is thought to be the first report of B. exigua var. exigua causing disease in pyrethrum. Boeremia blight is likely to contribute to the fungal disease complex causing reductions in green leaf area in Australian pyrethrum production.