Sclerotinia is a very widespread and serious disease of carrots,affecting both yield and quality and growers should be integrating both culturaland 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 carrotclipping machine has been developed and is being used commercially in the UKand in Israel. One more year of resultsto add to the other four years is showing consistently that clipping reducesSclerotinia control later in the season. Developed in conjunction with BASF andWroot Water, the canopy clipping technique involves clipping foliage betweenthe rows when the carrot foliage starts to fall over. Clipping the foliageallows more air movement in the canopy and disease pressure is reduced.
New work last yearevaluated the incidence of Sclerotinia across the bed. It seems that themajority of this disease is found on one side of the bed, usually the windward orshady side, because of the way the carrot flops over, creating a dampenvironment.
Howard advises howeverthat there is no need to make any alignment adjustments of the machine as thereare discs both side of the bed. He says that there are two units already workingin the UK, covering Lancashire, Shropshire, Lincolnshire, Nottinghamshire and itis being evaluated in Norfolk. The three-bed clipper follows drilling patternsand has a speed of operation of up to 10 kms/hour; meaning between 200-300acres can be clipped per day.
We now have fiveyears field experience with this cultural technique and it clearly reduces theSclerotinia infection by an average of 56%. The use of an effective chemicalsuch as Signum can then be integrated into the control programme.
Howard says that theuse of the three-bed clipper doesnt take away the need for a timely fungicideprogramme but may reduce the need for later fungicide applications. The way to reduce Sclerotinia is to use aneffective fungicide programme in conjunction with cultural control.
The extent ofdisease risk and fungicide timing is indicated by the ADAS/BASF SclerotiniaMonitoring, which monitors patterns of sclerotial germination each week for tenweeks from June through to August. The most recent ADAS/BASF SclerotiniaMonitoring bulletin indicates that fungicide applications need to be done nowon the earliest drilled crop Carrot crops are vulnerable to infection by Sclerotinia from June through toOctober, when the resting bodies or sclerotia germinate. Sclerotia germinatewhen the soil is moist and soil temperatures are 10C and above. Growers should start their fungicide applicationsearly, before the canopy closes over, as once Sclerotinia is in the crop it isalmost impossible to get on top of it, says Dr. Faye Ritchie of ADAS.
Robert Storer, FieldVegetable Product Manager for BASF, says that Signum is fully approved incarrots and provides broad-spectrum disease control of Sclerotinia, Alternariaand Powdery mildew as a protectant fungicide. It should be placed at the base of the plantwhere infection starts and where old leaves come into contact with the ground. TheSclerotinia fungus invades diseased, senescing or decaying leavesof the carrot crop, particularly those in contact with the soil. Roots are infected via the leaf petioles and through the crown. Sostarting the control programme before the canopy closes over is advisable. Aclosed canopy shields the base of the plant from fungicide sprays.