Photo 1. Irregular-shaped spots, brown with grey centres, occur on the leaves, and in wet weather develop into a blight.
Celery early blight
Widespread. In North and South America, Asia, Australia. The disease has been recorded from Samoa.
The fungus develops on the older, outer leaves first. It produces small yellow spots (up to 12 mm diameter) on the leaves and these develop rapidly in wet weather, becoming irregular in shape with greyish centres (Photos 1-3). Spores are produced mostly on the underside of the spots. The affected areas become dry and papery. When conditions favour the disease, elongated spots also occur on the leaf stalks.
The fungus survives on crop remains, and also in seed. Spores are spread short distances in water-splash, on machinery and people; spores are spread long distances by wind, and also on seed.
In Samoa, the disease has been recorded on celery throughout the year, and can be very damaging on the leaves.
Look for the small yellow spots, enlarging to irregularly rounded spots with greyish centres. Look for the infected areas that rapidly become dry, papery, and develop into a blight.
Seed treatment: Treat seed with thiram fungicide. Treatment with thiram will also prevent seedling damping-off.
In the field: Fungicides are commonly used to control this disease, and both protectant (e.g., mancozeb, copper formulations and chlorothalonil), and systemic products (e.g., those in the strobilurin and demethylation-inhibiting groups) are used.
AUTHOR Grahame Jackson
Information (and Photo 1) from Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, Tony Cooke, Susan House. CSIRO Publishing; and from Gerlach WWP (1988) Plant diseases of Western Samoa. Samoan German Crop Protection Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) Gmbh, Germany. Photo 2&3 Jacquie (Wright) Kami, formerly Plant Pathologist, Secretariat of the Pacific Community, Suva, Fiji.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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