APSnet Image of the Week

APSnet Image of the Week - Ray Blight on Tanacetum cineariifolium (pyrethrum)

Figure 1. Diseased bud affected by Phoma ligulicola.

Figure 2. Numerous dark pycnidia of Phoma ligulicola in infected pyrethrum plant tissue.

Contributed by Dr. Sarah Jane Pethybridge
University of Tasmania – North West Centre
P.O. Box 3523, Burnie, Tasmania 7320, Australia
sarah_jp@utas.edu.au

Host: Tanacetum cineariifolium (pyrethrum)
Disease name: Ray Blight
Pathogen name: Phoma ligulicola

Ray blight is the most severe fungal, foliar disease of pyrethrum in Tasmania, Australia. Since its first description in 1995, it has caused significant losses annually. Outbreaks generally occur in early spring and affect all above ground parts of the pyrethrum plant. The disease does not affect roots, but the pathogen is able to survive as epiphytic mycelium around root cuttings. This is one way it is transmitted symptomlessly on chrysanthemum and pyrethrum cuttings. The flower phase of the disease (figure 1) is the most characteristic symptom of the disease. Other symptoms include necrotic spots on leaves and lesions on stems. Signs include numerous pycnidia in infected tissue (figure 2).

APS publication number: IW000029

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