TOMCAST (FAST - Dew) model

Alternaria - TOMCAST (FastDew)

The model calculates the risk of infection by leaf blight diseases caused by Alternaria, and is considered to be relevant for early blight of potato (Alternaria solani), Alternaria leaf blight of carrot (Alternaria dauci), and Cercospora leaf blight of carrot (Cercospora carotae).

1) Early blight of potato (Alternaria solani). Photo: NIBIO 2) Alternaria leaf blight of carrot (inset closeup show sporulation of Alternaria). Photo: Belachew Asalf, NIBIO 3) Cercospora leaf blight (Cercospora carotae) of carrot. Photo: Belachew Asalf, NIBIO.

The model is meant to be started at the first discovery of symptoms and will then calculate daily risk values (DSV: Disease Severity Value) based on mean temperature and leaf wetness hours for each day (Madden et al. 1978). A daily DSV represents the risk of infection in the preceding 24 hours. Daily DSV-values are summed until a threshold is reached and treatment is recommended. The model is designed so that accumulation of DSV is reset when spraying is carried out, and accumulation starts again from 0.

The model’s standard setup in VIPS is based on the calculation of DSV at temperatures from 13 to 29 °C and leaf wetness hours per day, as defined by Madden et al 1978. The threshold value for calculation of spray intervals is set to DSV = 20.

The Modified TOMCAST as described for early blight in potato in Danish field trials (Abuley and Nielsen, 2017), can be used by selecting a minimum temperature of 10 °C for calculation of DSV when activating the model. Threshold value for spray interval remains at DSV=20.

Screenshot from VIPS displaying model output through a season. In this case, three spray times have been registered, each time resetting the accumulated risk value (DSV).

Model start

Potato plants vary in their susceptibility to early blight throughout the season and will become gradually more susceptible. This means the need for protection will vary accordingly. The model is intended to be started when the first symptoms are seen, and the first treatment is carried out (severity below 0.1%).

This model works best as a private model in VIPS. This can be done with data from a private weather station or by selecting data from a publicly available weather station as listed in VIPS. See user guide. When starting the model, the user can decide whether to use the standard setup or select an optional minimum temperature and/or threshold value for DSV.

Private model outputs with risk alerts will appear along with other model outputs at the right side of the map at the VIPS front page, provided the user is logged in.

Model interpretation

The model output is green (no risk) at DSV values below 15, yellow (possible risk) from 15 to 20 and red (high risk) above 20. The risk value will be reset when a spray date is entered by the user.

Test and validation of the model

In Norway

The model has been tested in Norwegian potato and carrot crops since 2020. The threshold value for spray timing is set to DSV=20 based on experiences from other countries, and will be evaluated as part of the considerations in further adaptations to Norwegian conditions (Asalf et al 2024).

Internationally

TOMCAST is derived from the FAST dew model (Madden et al 1978), originally targeted at predicting early blight, Septoria leaf spot and anthracnose on tomatoes in North-America (Gleason et al 1995). In Denmark, the model is tested and adapted for use against early blight (Alternaria solani) in potato (Abuley and Nielsen 2017). The Danish modified version of the model set the minimum temperature for calculation of DSV to 10 degrees.

Contact persons

Håvard Eikemo (potato), and Belachew Asalf Tadesse (belachew.asalf.tadesse@nibio.no) (vegetables)

References

Abuley and Nielsen, 2017. Evaluation of models to control potato early blight (Alternaria solani) in Denmark. Crop Protection, 102, 118-128. DOI: https://doi.org/10.1016/j.cropro.2017.08.012

Asalf. B., Eikemo, H., Høgetveit, L-A., Nordskog B., and Hermansen, A. 2024. Evaluating TOMCAST model for predicting timing of fungicide applications to control Alternaria diseases in carrot and potato (Poster abstract). 13th International Epidemiology workshop, 9-12 April, 2024, Foz du Iguacu, Brazil. P. 05. PDF

Bounds, R. S., Podolsky, R. H., & Hausbeck, M. K. 2007. Integrating disease thresholds with TOM-CAST for carrot foliar blight management. Plant disease, 91, 798-804.

Gleason, M. L. 1995. "Disease warning system." Plant Disease 79.2: 113.

Madden, L., S. P. Pennypacker, and A. A. MacNab. 1978. "FAST, a forecast system for Alternaria solani on tomato." Phytopathology 68.9: 1354-1358.

Links for further information

Plantevernleksikonet: Alternaria-bladflekk i gulrot

Plantevernleksikonet: Tørrflekksjuke i potet

{
    "loginInfo": {
        "username": "example",
        "password": "example"
    },
    "modelId": "ALTERNARIA",
    "configParameters": {
        "sprayingDates": [
            "2018-07-02T22:00:00Z",
            "2018-07-30T22:00:00Z",
            "2018-09-04T22:00:00Z"
        ],
        "thresholdDSVTempMin": "10.0",
        "thresholdDSVMax": "20.0",
        "timeZone": "Europe/Oslo",
        "observations": [
            {
                "elementMeasurementTypeId": "TM",
                "logIntervalId": 1,
                "timeMeasured": "2018-08-11T00:00:00+02:00",
                "value": 10.46
            },
            {
                "elementMeasurementTypeId": "BT",
                "logIntervalId": 1,
                "timeMeasured": "2018-08-11T00:00:00+02:00",
                "value": 60
            }
        ]
    }
}