Sclerotinia is a very widespread and serious disease of carrots, affecting both yield and quality and growers should be integrating both cultural and chemical control methods to get on top of the problem.
According to Howard Hinds of Root Crop Consultancy, a pioneering cultural technique using a specially designed three-bed carrot clipping machine has been developed and is being used commercially in the UK and in Israel. “One more year of results to add to the other four years is showing consistently that clipping reduces Sclerotinia control later in the season. Developed in conjunction with BASF and Wroot Water, the canopy clipping technique involves clipping foliage between the rows when the carrot foliage starts to fall over. Clipping the foliage allows more air movement in the canopy and disease pressure is reduced.”
“New work last year evaluated the incidence of Sclerotinia across the bed. It seems that the majority of this disease is found on one side of the bed, usually the windward or shady side, because of the way the carrot flops over, creating a damp environment.”
Howard advises however that there is no need to make any alignment adjustments of the machine as there are discs both side of the bed. He says that there are two units already working in the UK, covering Lancashire, Shropshire, Lincolnshire, Nottinghamshire and it is being evaluated in Norfolk. “The three-bed clipper follows drilling patterns and has a speed of operation of up to 10 kms/hour; meaning between 200-300 acres can be clipped per day.”
“We now have five years field experience with this cultural technique and it clearly reduces the Sclerotinia infection by an average of 56%. The use of an effective chemical such as Signum can then be integrated into the control programme.”
Howard says that the use of the three-bed clipper doesn’t take away the need for a timely fungicide programme but may reduce the need for later fungicide applications. “The way to reduce Sclerotinia is to use an effective fungicide programme in conjunction with cultural control.”
The extent of disease risk and fungicide timing is indicated by the ADAS/BASF Sclerotinia Monitoring, which monitors patterns of sclerotial germination each week for ten weeks from June through to August. The most recent ADAS/BASF Sclerotinia Monitoring bulletin indicates that fungicide applications need to be done now on the earliest drilled crop “Carrot crops are vulnerable to infection by Sclerotinia from June through to October, when the resting bodies or sclerotia germinate. Sclerotia germinate when the soil is moist and soil temperatures are 10°C and above. Growers should start their fungicide applications early, before the canopy closes over, as once Sclerotinia is in the crop it is almost impossible to get on top of it,” says Dr. Faye Ritchie of ADAS.
Robert Storer, Field Vegetable Product Manager for BASF, says that Signum is fully approved in carrots and provides broad-spectrum disease control of Sclerotinia, Alternaria and Powdery mildew as a protectant fungicide. “It should be placed at the base of the plant where infection starts and where old leaves come into contact with the ground. The Sclerotinia fungus invades diseased, senescing or decaying leaves of the carrot crop, particularly those in contact with the soil. Roots are infected via the leaf petioles and through the crown. So starting the control programme before the canopy closes over is advisable. A closed canopy shields the base of the plant from fungicide sprays.”
