The soil-borne disease Sclerotinia can be controlled in carrots with a range of both chemical and cultural solutions, according to chemical company BASF and Plant Systems Ltd.
The multi-host fungus, which is thought to have increased in severity and distribution in recent years, can attack carrots, rape, peas, beans and cabbage.
It germinates in the spring and thrives on diseased or decaying leaves, especially those in contact with moist soils. Plants roots can also be affected via the leaf petioles and crown.
Once present, Sclerotinia can remain in soil for up to ten years and can act as a new source each time a crop is cultivated.
However, BASF and Plant Systems Ltd say there are ways of controlling the fungus in carrots.
Increased rotations and avoiding a lush crop canopy through careful management of nitrogen can be important, according to Howard Hinds of Plant Systems Ltd, as well as changing the way crops are watered: “Irrigation is a factor that increases disease risk, especially from hose reel and sprinkle irrigation,” he said. “It may be that drip irrigation will reduce infection risk, although this area requires further investigation. Early drilled crops also tend to be more at risk from Sclerotinia infection.”
Varietal resistance can also be used, the companies say; adopting a North American technique of clipping foliage between beds might help reduce infections and decrease the germination of fruiting bodies on the soil.
In the UK, Hinds says some growers and agronomists are using a Plant-Plus disease model as a guide to optimise spray programmes. The model assesses risk based on local weather conditions, weather forecasts, crop growth and variety. “In 2006 a new development includes the risk from dead leaves, which are a trigger for Sclerotinia infections, and are to be included in the predictive system.”
He advises fungicide programmes in carrots should be geared more towards Sclerotinia control, with Alternaria and powdery mildew being important but secondary factors.
The new fungicide Signum caught could also help, performing better than both tebuconazole and azoxystrobin in ADAS trials, although the correct dosage has to be used at the right time, according to BASF’s Field Vegetable Product Manager Dave Marris: “As infection takes place on petioles and leaves below the canopy, it is essential to make the first application of Signum before the crop canopy closes over or before an infection period has occurred if Decision Support Systems are used. The dose rate should be 0.75 kg/ha for Alternaria and powdery mildew or 1 kg/ha for Sclerotinia control. Water volumes of 200 to 900 litres per hectare are advisable in order to improve spray penetration, dependent on canopy size and density,” he said.
No comments yet