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Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

Carrot leaf spot (135)

Photo 1. Small, dark angular spots of Alternaria leaf spot caused by Alternaria dauci. During humid weather the spots join together developing into a blight - a rapid death of the leaves.

Photo 2. Blight of carrot leaves caused by the carrot leaf spot fungus, Alternaria dauci.

Photo 3. Leaf blight of carrot, Alternaria dauci.

Photo 4. Leaf blight of carrot, Alternaria dauci.

Summary

Worldwide distribution. On members of the carrot or parsley family: mostly carrot, but also celery, dill, parsley, parsnip, wild carrot. A serious fungal disease of wet weather.
Spots on older and then younger leaves, becoming a blight as spots merge, and leaves blacken. It also causes damping-off.
Spread is in wind-driven rain, and on or in seed.
Cultural control: certified seed or hot water (50°C for 25-30 mins.); tolerant varieties; nursery hygiene: clean trays, pasteurise soil or soilless mixes, monitor and discard infected plants; do not plant too densely; weed; collect and burn trash or plough in remains after harvest; 3-year crop rotations.
Chemical control: seed - captan or thiram; field – copper, mancozeb, or those in strobilurin and DMI (demethylation inhibitor) groups of fungicides, alternating with either of the first two.

Common Name

Carrot leaf spot, Alternaria leaf spot of carrot

Scientific Name

Alternaria dauci. Note, another fungus, Cercospora carotae, produces similar symptoms.

AUTHOR Grahame Jackson
Information (and Photo 1) is 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 Kohler F, Pellegrin F, Jackson G, McKenzie E (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty Limited, Canberra, Australia. Photo 3 David B. Langston University of Georgia. Photo 4 McKenzie E (2013) Alternaria dauci PaDIL - (https://www.padil.gov.au).

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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