Well-advanced oilseed rape crops plus warm temperatures and lengthening days come together to bring forward the risk of Sclerotinia, according to the BASF/ADAS Sclerotinia Monitoring Service, which started this week. The monitoring service reports that the mild but wet weather is expected to promote early activity of sclerotia, with some germination already seen at the Devon site.

“This is in contrast to last year when the first germination wasn’t seen until the start of April at the Exeter depot, says ADAS plant pathologist Dr. Caroline Young.  She goes on to warn growers that there are very forward crops of oilseed rape this year, with flowering already visible in many fields and some southern crops already into the start of stem extension following warmer temperatures and lengthening days.  “We expect that for most crops, sclerotial germination will start ahead of flowering or coincide with the start of flowering this year.”

"The Sclerotinia monitoring information is generated from six sites nationally - Cambridgeshire, Yorkshire, Herefordshire, Lincolnshire, Kent and Devon. The data gathered is used to generate a local risk assessment based on local climatic conditions," she explains.

Germination assessments are made each week for a 12 week period; so will run into June, and results are updated every Friday or Monday on the website www.totaloilseedcare.co.uk. Each site is further supported by petal tests at first flower, early flower and mid-flower, which will help establish disease pressure from air-borne spores. Publication of when the latest bulletin is available will also be posted on Twitter; @totaloilseeds.

Caroline advises growers to check Sclerotinia risk for their individual postcodes by using the Sclerotinia Outlook service on the www.totaloilseedcare.co.uk website and to make decisions on PGR treatments on forward crops with good plant stands.

“Last year, as a result of over 10 years’ worth of Sclerotinia monitoring experience gained by ADAS and BASF, the monitoring service expanded to include this postcode-based outlook. By using this free service on the totaloilseedcare website, growers and advisors can gauge just how the Sclerotinia risk is shaping up for the season on a local basis 24/7. Feedback on this new local development, Sclerotinia Outlook has been very positive," says Jonathan Ball of BASF.

The service provides a colour-coded outlook (green for least likely and red for most likely) and regional guidance based on the likelihood of sclerotial germination in a particular postcode area.

Caroline Young of ADAS believes that the service will be very useful this year as Sclerotinia infection risk is likely to be moderate to high at early flowering.  “As a priority growers should be prepared to make spray applications at early to mid-flower stage. Oilseed rape flowering is early this year, beginning now in the South West and South East. Sclerotinia, too, will be early.”

Caroline reminds growers that a soil temperature of 10°C is needed for sclerotia to germinate actively.  “Rape crops are at highest risk when sclerotial germination synchronises with early flowering. Spores infect the plant when minimum temperatures are above 7°C and there are long periods of high humidity. You need to apply fungicide treatments before infection and this is where the Outlook service will be most useful. By using the Outlook service, it can help to prioritise spraying demands over the next few weeks.”

Sclerotinia is an important disease of oilseed rape, causing yield losses of 30 to 50% in severely affected crops. It is therefore important to protect crops at risk. BASF's Jonathan Ball adds that, “fungicides are mainly protectant so it is important to know when disease is likely to come into the crop. Knowing this information puts you in a better position to time fungicide applications correctly, in advance of disease and before any significant petal fall. BASF advise growers to start their programme with an early Sunorg Pro on the many vigorous crops and use an early to mid-flower fungicide treatment of Filan (boscalid) at 0.3-0.5 kg/ha before petal fall.”

Both Filan and prothioconazole-based fungicides give excellent control of Sclerotinia, but a number of other important considerations make Filan the product of choice for 2014:

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• Yield increase in the absence of disease demonstrated by the HGCA trial summary 2010-2012.  Filan produced  0.25 t/ha (£70/ha) over untreated crops
• A different mode of action for resistance management of Light Leaf Spot – triazole resistant strains of Light Leaf Spot exist. Since spores will still be present in the crop, FRAG guidelines say avoid the same actives used earlier against Light Leaf Spot when targeting Sclerotinia at flowering.
• Bee-safe – can be mixed with pyrethroids for seed weevil control at flowering. However as with all sprays ensure that bees are not foraging actively in the crop at the time of spraying.