Time to start Sclerotinia prevention programme in carrots

The BASF and ADAS sponsored Sclerotinia monitoring system for carrot growers has recorded sclerotial germination and indicates that the first fungicide treatments will be required soon as main crops approach full ground cover.

Dr. Peter Gladders from ADAS Boxworth explains that sclerotia are now germinating in carrots and barley in Norfolk and in some winter arable crops in the south and east. Rainfall or irrigation could allow more sclerotia to germinate in carrot crops sown in April or late May, where soils remain moist for several days. Main crops sown in early May are at the 5 to 7 leaf stage and are growing rapidly. The time to apply the first fungicide, just before canopy closure, is approaching.

Howard Hinds, specialist root crop consultant, explains that early drilled carrot crops hit dry conditions, struggled to establish and are a little more patchy in terms of their growth, but the later drilled ones look better. Early drilled crops are more at risk from diseases such as Sclerotinia and cavity spot, so need an integrated programme of chemical and cultural control to keep disease at bay.

Although we have excellent chemistry, such as Signum, to control Sclerotinia in carrots, the disease is so destructive that we need to optimise all the tools we have to prevent this disease, he says.

Solely in conjunction with BASF, Howard Hinds and Wrootwater has been developing a new canopy clipping technique which involves clipping foliage between the rows when the carrot foliage starts to fall over. This allows more air movement in the canopy and so reduces disease pressure. Initially we were working with a single bed clipper which uses a round disc to cut into the edge of the bed, but now with BASF sponsorship, we have developed a three-bed clipper which fits in better with drilling and cultivations. Not only is the three-bed clipper more accurate, following drilling patterns, but it is also much quicker. It is an exciting new development.

Howard points out that the development of the three-bed clipper wont take away the need for a sound and timely fungicide programme but may, if the trials prove, help reduce the later fungicide applications. The way to reduce Sclerotinia is to use an effective fungicide programme in conjunction with cultural control. The first fungicide application, which is normally Signum, is applied when the crop is still standing and before it has closed over. The spray should be targeted into the bottom of the crop to cover the soil between the rows.

Howard considers Signum to be a particularly strong Sclerotinia fungicide and uses it early in the programme. I usually recommend Signum as the first and third fungicide spray and integrated it in a programme with other Sclerotinia-active fungicides with a different modes of action. It needs to be integrated into the programme with other chemistry in order to comply with its label recommendations of two sprays and also to minimise any resistance risk. Then as we move towards the end of July and August, the clipping regime can start as the crop starts to lodge over.

Rob Storer, Field Vegetable Product Manager for BASF, advises that, as Signum is a protectant fungicide, it needs to be placed at the base of the plant before infection starts and where old leaves come into contact with the ground. The first Signum spray should be applied before the crop canopy has closed over and the ground is still visible. A closed canopy not only creates the right conditions for further infection, but shields the base of the plant from fungicide sprays.

He points out that Signum provides broad-spectrum disease control of Sclerotinia, Alternaria and Powdery Mildew. Trials data also show that Signum gives good control of diseases responsible for the loss of yield and quality in carrots such as Cercospora, Black Liquorice Rot and Acrothecium.

A protectant and systemic fungicide, Signum contains 267g/kg boscalid and 67g/kg pyraclostrobin, formulated as a water dispersible granule. It is recommended in carrots as a protectant spray or at the first signs of disease for the control of Sclerotinia, Alternaria and Powdery Mildew at a dose rate of 0.75 to 1 kg/ha in 200-900 litres of water. Two applications can be made to the crop. It is subject to LERAP B and has a harvest interval of 14 days in carrots. It should be alternated in a programme with other fungicides with an alternative mode of action as part of an anti-resistance strategy.

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