Initially visible as dark brown lesions on the individual leaflets and petioles and these lesions can be surrounded by a yellow halo. The first infections are often found on the leaflet edges of older carrot leaves. Under favourable conditions these can coalesce to shrivel and blacken whole leaves or aerial parts of plants to give a `blighted` appearance (as the name suggests). Like Cercospora, this fungus does not invade the carrot roots.
Infections arise on older leaves. Can be carried on the seed, wind borne or spread by rainsplash. Known to survive on crop debris for periods of up to 2 years. Can also survive on host plants such as wild carrot as well as being able to survive in the soil for periods of up to a year.
Prolonged heavy rainfall and cool temperatures.
Does not invade plant roots. Weakened foliage can impair healthy root development as well as causing mechanical harvesting difficulties especially where disease pressure is severe. Can also be found on parsley.