United Kingdom
June 13, 2014
In highly infected fields, carrot losses could be as high as 50% as a consequence of the disease Sclerotinia. It is important therefore to monitor the crop carefully in order to assess disease risk and be in a position to plan a cost-effective preventative disease control programme. The BASF and ADAS sponsored Sclerotinia monitoring system for carrot growers starts this week and growers and advisors can log-on every week for the next 10 weeks to the Carrot Sclerotinia Monitoring.
Dr. Caroline Young from ADAS explains that carrot crops are usually vulnerable to infection by Sclerotinia from June through to September, when the resting bodies or sclerotia germinate. “Sclerotia germinate when the soil is moist and soil temperatures are 10°C and above. At this point in the year, soil temperatures have been exceeded and the soil is plenty moist enough.”
“Currently the risk of sclerotinia infection is low but this could change soon. The risk of Sclerotinia is based on three factors – firstly are there sufficient sclerotia at the soil surface of the carrot field? Secondly is there sufficient moisture and soil warmth to encourage germination, which results in airborne spore inoculum? And thirdly is the crop at a vulnerable stage? Carrot plants that are young and vigorous and where there is still good air movement around the bed are not so vulnerable to Sclerotinia. The most vulnerable stage is when leaves start to senesce at the base of the plant.”
The ADAS/BASF Sclerotinia monitoring system monitors sclerotial germination each week from June through to August. It indicates the extent of disease risk and the need for fungicide treatment. Growers should check the published information on the AgriCentre web site weekly and be ready to take the right action at the right time.
“Most carrot growers start their fungicide applications, before the canopy closes over, so that they are able to get their fungicide right down to the base of the plants. The approach is mainly protectant as, once Sclerotinia is in the crop, it is almost impossible to get on top of. 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.”
Dr. Young reports that some carrot crops planted early this year are surprisingly advanced already. “Normally canopy closure takes place from mid-June to late July, depending on sowing date and growing conditions. Most growers would go for a three spray fungicide programme, with the sclerotinia-targeted sprays starting in June or July. What you need to do is the cover the plant with a fungicide before it gets too difficult to do so and alternate different chemistries as a resistance strategy.”
Robert Storer, Field Vegetable Product Manager for BASF, agrees that monitoring, timing and fungicide application are important for the successful prevention of Sclerotinia in carrots. “Signum is a protectant fungicide and it should be placed at the base of the plant where the infection starts and where old leaves come into contact with the ground. The first Signum spray is recommended before the crop canopy has closed over and the ground is still visible. A closed canopy shields the base of the plant from fungicide sprays. It should be alternated in a programme with other fungicides with an alternative mode of action as part of an anti-resistance strategy and it can be applied twice to any crop. ”
“Signum is fully approved in carrots and provides broad spectrum disease control of Sclerotinia, Alternaria and Powdery Mildew. The physiological, AgCelence, benefits of Signum are not insignificant and play an important role in maintaining the canopy greener for longer,” says Rob Storer.
Dr. Young also points out that avoiding fields with infected soil for a period of 3 to 5 years would be helpful. “This is particularly so when crops are on grown on rented land. You need to know past cropping to implement an effective rotation.”
Species
