Carrot growers should start their fungicide programmes earlier with a treatment of Signum, a boscalid and pyraclostrobin formula, which also controls powdery mildew and Alternaria, advised Howard Hinds of Howard Hinds Crop Consultancy.

“I have noticed that Sclerotinia has become a much more widespread and serious disease in this crop. Consequently carrot growers are getting a lot tighter with their fungicide programmes and are starting their programmes earlier. They are also using more robust programmes right from the start,” says Hinds, who has 10 years’ experience in carrot crop consultancy.

Howard advises growers to start the programme with Signum as he regards it as one of the strongest products against the main disease Sclerotinia. “Once Sclerotinia has become established, it is very difficult to keep on top of, so ideally I would advocate the use of a strong and robust first spray, such as Signum.”

“With infection taking place on older stems and leaves below the canopy, it is important to make the first application of Signum before the crop canopy closes over or before an infection period has occurred according to Decision Support Systems. This allows the product to get right down into the crop. Usually the first application is made around early July when the crop coverage is 50 to 70 per cent of the ground. Water volumes need to be sufficient to give good spray penetration,” said Hinds.

A second spray of Signum should be applied after a fungicide with an alternative mode of action such as tebuconazole has been used.

“The reason that you need a strong start to the control programme is largely explained by looking at the life cycle of Sclerotinia. The resting bodies or sclerotia remain viable in the soil for up to ten years and can act as a new source each time the soil is cultivated. Sclerotia germination occurs in the spring during warm and showery weather. The fungus then invades diseased, senescent or decaying leaves, flourishing on dying leaves in contact with moist soils. The roots are infected in the field via the leaf petioles and through the crown. So you need a strong and effective fungicide used at the right rate and in the right water volumes to prevent the disease getting an early hold. As both active ingredients in Signum are protectants, the aim is to place them at the base of the plant where infections start,” explains Dave Marris, field vegetable product manager for BASF.

There is also a new disease risk modelling initiative, looking at placing sensors in the crop rather than above the crop. According to Hinds, this is proving to show significant differences that can be used to improve the timing of early fungicide sprays.

“Fungicides play a key role in the integrated control of Sclerotinia. Fungicide programmes in carrots are geared more towards Sclerotinia control, with Alternaria and powdery mildew being important but secondary targets. Signum performs very well on all three diseases. In ADAS [Agricultural Development and Advisory Services] trials Signum outperformed both tebuconazole and azoxystrobin,” said Marris.