The BASF and ADAS sponsored Sclerotinia monitoring system for carrot growers starts at the beginning of June and growers and advisors are invited to log-on every week to the carrot Sclerotinia Monitoring link on www.agriCentre.basf.co.uk in order to assess their disease risk and plan an effective preventative disease control programme.
Dr. Peter Gladders from ADAS Boxworth explains that 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. So far this year we barely reached this temperature until the end of April, but in oilseed rape where sclerotia germination of Sclerotinia has been monitored since mid-March we have been finding more germination than last year. Carrot growers can pick up the tail-end of the arable crop monitoring, where germination of sclerotia reached over 54% last week in one location and petal tests have shown over 77% sclerotinia infection. So despite the cold conditions there is still activity."
Dr Gladders explains that 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."
The ADAS/BASF Sclerotinia monitoring system monitors patterns of germination each week and indicates the extent of disease risk and the need for fungicide treatment. In carrots there is a later germination than in winter arable crops because of spring cultivations. "Growers should check the published information on the AgriCentre web site weekly and so be ready to take the right action at the right time," Dr. Gladders advises.
"Carrot growers usually start their fungicide applications early, before the canopy closes over, which is sensible as once Sclerotinia is in the crop it is almost impossible to get rid of it. Most carrot crops are now planted and the earlier ones have 3 or 4 leaves, but most crops have low ground cover so far. Irrigation could stimulate further germination and hence the fungicide programme may need to start in crops sown in April or early May in the next three or four weeks."
Robert Storer, Field Vegetable Product Manager for BASF, agrees that timing is key to the successful prevention of Sclerotinia in carrots. "Signum is a protectant fungicide and it needs to be placed at the base of the plant where 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."
"Signum is fully approved in carrots and provides broad spectrum disease control of Sclerotinia, Alternaria and Powdery Mildew. Trials data show that Signum also gives good control of diseases responsible for the loss of yield and quality in carrots such as Cercospora, Black Liquorice Rot and Acrothecium," says Rob Storer.
He reports that trials and commercial usage show that Signum is an effective option. "In ADAS trials Signum gave 58% control of Sclerotinia, compared with just 5% for azoxystrobin and 28% for tebuconazole. For Alternaria, Signum also gave the highest level of control, reducing infection levels to 19% from 55% in the untreated, with azoxystrobin reducing infection down to 30% and tebuconazole to 28%."
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.
