Disease update on Sclerotinia in Carrots
The carrot Sclerotinia monitoring system, is showing early germination of sclerotia at all sites. Overall the risk to main crop carrots from this disease is high this year. The wet and humid conditions have favoured Alternaria and Cercospora. Growers are being advised to inspect their crops now in order to guide their timely fungicide use, according to ADAS and BASF.
ADAS report that the heavy rain has helped Sclerotinia to germinate very early this season, within four weeks of drilling. This is two weeks sooner than last year and reflects the high rain and continuously moist soils. In areas with Sclerotinia, main crop carrots should be considered at risk from four to six weeks after drilling.
ADAS also report that there are still some air-borne spores being produced from sclerotia of Sclerotinia present in over-wintered arable crops. This provides another opportunity for the disease to spread to carrots and other vegetables from nearby fields.
According to ADAS, carrots sown in mid-April have generally reached the 6-8 leaf stage with 100% ground cover in the beds. The first leaves are now senescing and Sclerotinia infection may soon start to appear. ADAS are recommending that fungicides should be applied at this stage to protect the foliage against the high disease risk.
According to BASF, Signum has outperformed other competitor fungicides for the control of major carrot diseases, Sclerotinia, Alternaria and Powdery mildew. Trials also show good control of Cercospora leaf blight.
"The key to its successful use of Signum in carrots is timing. Both active ingredients in Signum (boscalid and pyraclostrobin) are excellent protectants, but they need to be placed at the base of the crop where infections of Sclerotinia start. Timely application ensures protection of the leaves before infection can take place. Control of diseases like Alternaria and powdery mildew prevents dead leaves becoming a nutrient source for Sclerotinia," says Matthew Blaken, Field Vegetable Product Manager for BASF.
"Prolonged protection can be obtained by applying a second spray of Signum (following an application of a fungicide with an alternative mode of action). This second application will ensure the continued benefits of the strong protectant and physiological properties of Signum and will help to prevent dead leaf material acting as a food source for Sclerotinia," says Matthew.
Sclerotinia has become more widespread and troublesome in carrots, causing rotting of roots and foliage and decreasing yield and quality. Alternaria can also cause economic damage if allowed to develop in warm and wet conditions. Powdery mildew was a problem last year when the conditions were drier and it is already very active in various other crops this season. Cercospora is an increasing threat to carrots and other crops such as sugar beet.
Background Notes – A protectant and systemic fungicide, Signum contains 267g/kg boscalid and 67 g/kg pyraclostrobin, formulated as a water dispersible granule. It is recommended in carrots for the control of Sclerotinia, powdery mildew and Alternaria. It is recommended in carrots as a protectant spray or at the first signs of disease 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.
