Cercospora leaf spot of fennel

Symptoms

Small brown spots with dark borders + yellow halos on feathery foliage, severe infection causes premature defoliation + bulb quality reduction, bulbs from infected plants store poorly + develop secondary rots, plants in dense stands worst affected.

Plants affected

• dill
• fennel

Easily confused with

• grey mould (Botrytis)

  How to tell them apart: Cercospora foeniculi produces discrete, well-defined leaf spots on dill foliage: small (1-3 mm) angular-to-rounded lesions with tan-to-grey necrotic centres and a darker reddish-brown margin, sometimes with a faint chlorotic (yellow) halo. The dead centres stay dry and papery, and spots remain scattered on the fine leaflets without dense fuzz. Botrytis cinerea instead causes spreading, water-soaked, soft brown blight that collapses whole leaflets and stems, and in humid conditions develops a conspicuous velvety grey-brown mould (sporulation) over the dead tissue. The decisive sign: Botrytis is wet, soft-rotting and grey-fuzzy and starts from wounds or dense canopy; Cercospora is dry, sharply spotted and bordered with no grey fuzz.

Common questions

How do I recognise Cercospora leaf spot of fennel on dill?

Small brown spots with dark borders + yellow halos on feathery foliage, severe infection causes premature defoliation + bulb quality reduction, bulbs from infected plants store poorly + develop secondary rots, plants in dense stands worst affected.

Do I have to report Cercospora leaf spot of fennel?

No. Cercospora leaf spot of fennel is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is Cercospora leaf spot of fennel treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.