Celery and parsley were originally cultivated for medicinal purpose, and it was later developed into a food and flavouring crop. It is attacked by a number diseases that affect yield and quality. Septoria leaf spot is an important foliar disease of both celery and parsley crops world-wide.

The aim of the study was to investigate in more details the pathogen Septoria apiicola and S. petroselini, occurring very often in Yugoslavia.

Many strains of a pathogenic fungus were isolated from diseased celery and parsley leaf tissue. Leaf spots symptoms, characteristics for natural infection, were also reproduced by artificial inoculation of plants in greenhouse. Influence of temperatures and leaf wetness on disease severity was investigated. Pathogen survival in the leaf debris and on the seed were studied. The objective of the research was pathogenicity of isolates of S. apiicola and S. petroselini on different host plants and susceptibility of celery cultivars to S. apiicola.

The highest number of leaf spots was recorded at 250 C for 72 hours and the lowest at 100 C and 300 C. Lesions formed as early as 9 days after inoculation follows wet periods of 24-48 hours. The viability of the pathogens in leaf debris lasted within the period of eight to over 12 months. The pycnides viability on the celery seeds lasted about 14 months.

The isolates of the pathogens showed highly specialised. Isolates of S. apiicola caused leaf spot in celery, and isolates of S. petroselini in parsley.