Sclerotinia has become a much more widespread and serious disease and carrot growers are adopting a broad approach to controlling this soil-borne disease, using a range of cultural and chemical solutions, advises BASF and vegetable consultant Howard Hinds.
"One of the main problems with Sclerotinia is that it has a range of host crops including oilseed rape, potatoes, peas, spring beans, cabbage and carrots. So it is difficult to keep it out of the rotation. With its resting bodies or sclerotia remaining viable in the soil for up to ten years and acting as a new source each time the soil is cultivated, it is inevitable that this disease has increased in its incidence," explains Robert Storer, Field Vegetable Product Manager for BASF.
Most growers have now adopted an integrated approach to controlling this disease by introducing ways of reducing disease pressure as well as timing chemical control more accurately. There are already a number of actions that carrot growers can take and several more that are being developed, according to Howard Hinds of Howard Hinds Crop Consultancy.
"For example, BASF sponsor a Sclerotinia monitoring system that helps carrot growers assess disease risk, predicts when to apply their first fungicide treatments and so helps plan an effective control programme. Starting in June, weekly results are published on the Carrot Sclerotinia Monitoring link on www.agriCentre.basf.co.uk. The service is based on monitoring the germination pattern of sclerotia. Sclerotia germinate usually when soil is moist and temperatures are between 5°C -25°C, with optimum temperatures being 15°C-25°C."
Howard continues to explain that after the soil borne sclerotia germinate, they develop small mushroom-type bodies called apothecia which release spores under the crop canopy and these infect senescing plant tissue near or on the soil surface. From there the disease can infect the crop stems and leaves and eventually the root crowns, resulting in core rots. So it is vital that the first fungicide spray such as Signum is applied early before the foliage has a chance to close over and starts to senesce. Once the disease is in the crop, it is impossible to get rid of it."
"The key objective of any disease monitoring approach is to provide growers with the information they need in order to use their chemicals in the most timely and economic fashion. With the aid of in-crop devices to measure soil temperature and rainfall, the understanding of the exact conditions under which the sclerotia might germinate is certainly improving," he explains.
Robert Storer of BASF agrees that timing and application is key to the successful control of Sclerotinia in carrots and so an accurate monitoring service is important. "As Signum is a protectant fungicide, it needs to be placed at the base of the plant where the infection starts. Sclerotinia spreads when the old leaves come into contact with the ground and the closed canopy also creates a microclimate favourable to further disease development. The first Signum spray should be applied before the crop has closed over completely and the ground is still visible."
Howard Hinds says that growers can also try to reduce the overall disease pressure by managing nitrogen. "As nitrogen encourages a lush canopy with leaves that tend to lodge and come into contact with soil, lowering its use will help reduce disease risk. Irrigation is another factor that increases disease risk, especially from hose reels where large droplet sizes can cause canopies to fall over," says Mr. Hinds.
"Another interesting way of reducing infection is a new technique for the UK, but not new to Canada. This involves managing the crop canopy by clipping foliage between the rows to allow more air movement in the canopy, particularly important for the variety Nairobi which is prone to collapse, and decrease disease risk. In the UK, our flat beds system of growing carrots means that just the outside of the beds can be clipped; however in 2008 trials this was still shown to decrease infection by 50%. Canadian growers have a different planting configuration and are able to clip between individual sets of rows. The technique has been so successful in reducing Sclerotinia infection that it is now being used on a commercial basis "
For further comment and information please contact Robert Storer, BASF on 0161 488 5731 or 07768 464037 (mobile)
