Sclerotinia control measures in main crop carrots
As main crop carrots are now at risk from Sclerotinia as well as from a range of other foliar diseases, fungicide treatments should be programmed at tight intervals and should start just before canopy closure, according to the BASF and ADAS sponsored Sclerotinia monitoring system for carrot growers.
The ADAS/BASF Sclerotinia Germination Tool monitors patterns of sclerotial germination and indicates disease risk and fungicide timings each week for a ten week period from June through to August.
The most recent and last ADAS/BASF Sclerotinia Monitoring bulletin of this growing season indicates that many main crop carrots are now at the 9 to 10 leaf stage, with first signs of leaf senescence on the oldest leaves.
Cotyledons and first leaves become susceptible to Sclerotinia as they senesce and some crops have been damaged by hail. Carrot sclerotia are germinating in moderately high numbers at the Nottinghamshire and Cambridgeshire sites.
The continuing showery weather and crop canopies with full ground cover favour more germination to come.
Disease risk will be high where leaf senescence has started and where crops start to lodge, warns Dr. Peter Gladders from ADAS Boxworth.
“Carrot crops are vulnerable to infection by Sclerotinia from June through to October, when the resting bodies or sclerotia germinate. Foliar fungicides are required before foliar canopies close within the beds and then in a programme to continue protection of the foliage. Growers should continue checking for foliar disease in forward crops as disease risks could be high this season if showery conditions continue.”
Robert Storer, Field Vegetable Product Manager for BASF, says that the first Signum spray is recommended before the crop canopy has closed over and the ground is still visible. “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. This year risk the risk of other foliar diseases appears to be high and growers are being advised to monitor for Alternaria and Cercospora leaf blights at weekly intervals as well as noting Sclerotinia. Starting the fungicide control programme just prior to canopy closure is advisable. This should be followed by a tight programme of fungicides with different modes of action to maintain disease protection in such a high risk season and to minimise resistance pressure.”
“Signum is fully approved in carrots with two sprays per crop being advised. It provides broad-spectrum disease control of Sclerotinia as well as control of Alternaria and powdery mildew. In ADAS trials, Signum gave 58% control of Sclerotinia, compared with 5% control for azoxystrobin and 28% control for tebuconazole. For Alternaria, Signum 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%. Where powdery mildew was the target disease, the untreated suffered 62% infection but Signum reduced this to just 3%, compared with azoxystrobin and difenoconazole resulting in 10% infection,” reports Rob Storer.
