The BASF- and ADAS-sponsored tool, hosted on the BASF website, monitors sclerotial germination each week from June to August, indicating the extent of disease risk and the need for fungicide treatment.
Carrot crops are usually vulnerable to infection by the fungus when the soil is moist and soil temperature is above 10°C, allowing the resting bodies, or sclerotia, to germinate. This can lead to losses as high as 50 per cent in the worst-infected fields.
ADAS plant pathologist Dr Caroline Young said: "At this point in the year, soil temperatures have been exceeded and the soil is plenty moist enough."
She added: "Currently the risk of infection is low. Where there is still good air movement, young and vigorous carrot plants are not so vulnerable to Sclerotinia. The most vulnerable stage is when leaves start to senesce at the base of the plant."
Most carrot growers start their fungicide applications before the canopy closes over, to ensure it penetrates to the base of the plants, she explained.
"The approach is mainly protectant as, once Sclerotinia is in the crop, it is almost impossible to get on top of. You need to cover the plant with a fungicide before it gets too difficult, and alternate different chemistries as a resistance strategy."
BASF field vegetable product manager Robert Storer advised: "Signum is a protectant fungicide and it should be placed at the base of the plant where the infection starts and where old leaves come into contact with the ground.
"It should be alternated in a programme with other fungicides with an alternative mode of action as part of an anti-resistance strategy and it can be applied twice to any crop."
Young also recommends avoiding growing carrots for three to five years in fields known to have been infected. "When crops are on grown on rented land, you need to know past cropping to implement an effective rotation," she said.