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.