Outdoor celery: development of integrated strategies for the management of septoria leaf spot and other diseases

Septoria leaf spot (S. apiicola) of celery, also known as ‘late blight’, is the most destructive disease of field-grown celery crops. Initially seen as small brown spots on leaves, the disease can progress rapidly to cause extensive defoliation and render the whole crop unmarketable if left unchecked.

There are two potential ways to control septoria effectively using fewer spray treatments. Firstly, to use newer, more effective fungicides representative of different chemical groups. Secondly, to target sprays when infection risk is high or predicted to be high. Leaf wetness duration and temperature are strongly influential in the development of celery leaf spot and are obvious parameters to consider to aid spray decisions.

Project findings:

• Glasshouse tests revealed large differences in the relative protectant and curative activity of eight fungicides against celery leaf spot.
• The effects of leaf wetness duration and temperature on disease development were quantified, providing a rational basis for disease risk prediction.
• In an inoculated celery field trial, excellent control of septoria leaf spot was achieved using a fungicide programme of five sprays. Application timing was based on measured leaf wetness duration. Product choice was based on the relative protectant and curative activities of different fungicides combined with recent and forecasted rainfall/irrigation, to estimate disease risk. Spray applications were reduced by one, compared with a prophylactic spray regime.

See related AHDB Factsheet on the management of celery leaf spot

The expected deliverable from this project was an integrated strategy for improved control of leaf spot in field crops of celery developed by:

• Evaluation of newer fungicides representative of different chemical groups for their efficacy against celery leaf spot.
• Development of a spray-timing decision tool
• Highlighting cultural practices that minimise the risk of disease spread.