Although Sclerotinia has become a widespread and serious disease in many crops including carrots, it is important to be able to assess the level of risk in order to plan the most cost-effective prevention and control strategy.
Compiled by plant pathologist Dr. Peter Gladders of ADAS Boxworth, the new easy to use Sclerotinia risk assessment chart has been devised to help carrot growers.
The flow chart starts by asking about the history of Sclerotinia on the farm. "One of the main risk factors for Sclerotinia is that it infects a wide range of host crops including winter oilseed rape, spring oilseed rape, potatoes, peas, spring beans, cabbage and carrots. The pathogen survives in the soil as resting bodies or sclerotia, which can remain viable for up to ten years. If you have had Sclerotinia in carrots or in other crops in the same field, disease risk will be high," explains Robert Storer, Field Vegetable Product Manager for BASF.
"You should then consider specific crop associated factors and agronomic inputs, such as crop growth habit and crop nutrition. If the carrot canopy is vigorous and large or if early nitrogen has been applied there is a greater chance that leaves will come into contact with the soil surface and the Sclerotinia risk will be high. Similarly if the crop has lodged, risk of disease is high."
"Weather will also play an important part. If rainfall is above average, Sclerotinia risk is potentially very high. Prolonged rainfall over several days or high rainfall in August and September when dead leaves are present also mean high risk," explains Rob.
Robert explains that normally Sclerotinia initially enters the crop from spores released from cup shaped structures called apothecia; these grow out from the sclerotia that are present in the soil. Apothecia are produced when the soil is moist and temperatures are between 5° -25°C, with optimum temperatures being 15°-25°C. "The fungus then invades diseased, senescing or decaying leaves, particularly those in contact with moist soils. Roots are infected by the fungus via the leaf petioles and through the crown. A closed canopy also creates a microclimate favourable to further disease development. These epidemiological factors are pertinent to how risk is assessed."
In addition to the risk assessment chart, BASF are continuing to sponsor a Sclerotinia monitoring system to help carrot growers to predict when to apply their first fungicide treatments. Starting in June, weekly results will be published on the Carrot Sclerotinia Monitoring link on www.agriCentre.basf.co.uk.
"The service is based on monitoring the germination pattern of sclerotia. An accurate monitoring service is important, because timing and application of the mainly protectant fungicides is key to successful control. For example, Signum is a protectant fungicide and needs to be placed at the base of the plant where the infection starts. The first Signum spray should be applied before the crop canopy has closed and the ground is still visible. This monitoring service will help to make sure that the fungicide is applied at the correct time."
For further comment and information please contact; Robert Storer, BASF on 0161 488 5731 or 07768 464037 (mobile)
