Septoria apiicola model

This model calculates infection risk of Celery leaf spot (alt. Septoria late blight) (Septoria apiicola) using weather data and forecasts. The risk alerts apply to celery but are also relevant for parsley blight (Septoria petroselini) in parsley.

In Norway, celery leaf spot occurs sporadically, and the model is recommended as a tool to help determine when to intensify field inspections prior to the first detection of symptoms.

Celery leaf spot in celery. (Photo: Erling Fløistad, NIBIO)

The model for celery leaf spot is based on a calculation of when weather conditions are wet enough for the fungus to sporulate and cause infection in susceptible host plants.

Infection risk alerts are issued when a minimum of 12 consecutive hours of leaf wetness is recorded. Wetness periods are calculated based on leaf wetness measured 30 cm above ground level. At weather stations without ground-level sensors, leaf wetness measured at 2 m is used. Weather data is obtained from weather stations affiliated with the Agrometeorological service (Landbruksmeteorologisk Tjeneste (LMT)) and from 2-day forecasts by the Norwegian Meteorological Institute.

Interpretation of warnings

Red alert means high risk of infection and symptoms of celery leaf spot have been reported from the area/region association with the current weather station. Yellow alert means the weather conditions indicate risk of infections, but there are no recorded symptoms in the area. Green means no estimated risk of infection.

Model calculations are updated daily, based on observed weather data to present time and 2-day weather forecasts. Field observations and registration of celery leaf spot are carried out in collaboration with the Norwegian Agricultural Advisory Service.

Screenshot from detailed model outputs for celery leaf spot. Blue bars indicate periods of at least 12 consecutive hours of leaf wetness. Black bar indicates date of first field observation of Septoria leaf spot. Green, yellow and red background colors correspond to daily alert status on VIPSweb home page and in the table under detailed model outputs.

Season of model operation

Risk alerts are issued from weather stations in areas with celery production. The model is active from June through September. Please contact VIPS (vips@nibio.no) if there’s a wish for model calculations at additional weather stations, or a need for adjustments of the operating period.

Risk alerts for all activated weather stations are automatically displayed at VIPSweb front page map. A private setup with individually selected start and stop dates is available by use of private weather stations and weather stations affiliated with the LMT-network. See user guide. 

Test and validation of the model

The model is developed in Michigan, USA and published by Lacy (1994). In Norway, field trials with studies of weather conditions, spore formation and infection conditions were carried out at Ås during the period 2012-2016. The results showed that the model generally performs well, although its accuracy is slightly reduced during periods of rainfall (Nordskog and Le, 2014).

Recommendations for model use in Norway

The model for celery leaf spot is a tool to help assess when to look for early symptoms in the field. It is not considered accurate enough for timing of fungicide applications under Norwegian conditions.

It is recommended to intensify field inspections after periods with risk alerts to detect early
infections of celery leaf blight. If inoculum is present, infections are expected to develop 7-14 days after a period of infection risk alerts (yellow or red warnings).

For disease management, please contact your local agricultural advisor for assessment of current plant protection strategies.

References

Lacy, M.L. 1994. Influence of wetness periods on infection of celery by Septoria apiicola and use in timing sprays for control. Plant Disease 78, 975-979.

Nordskog, B. and Le, V.H. 2015. Varsling av selleribladflekk [Forecast of celery late blight]. Gartneryrket nr 6, s14-15. (Norwegian text)

Celery leaf spot description: Plantevernleksikonet

Contact person: Berit Nordskog

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