The ADAS/BASF web-based monitoring service on www.totaloilseedcare.co.uk is reporting the start of sclerotia germination, with 12% germination detected in Devon. This, together with apothecia being found near to the site in Herefordshire, indicate that the pressure is on to start protecting the oilseed rape crop from damaging Sclerotinia infection.

Jon Williams, Agronomy Manager for BASF, explains that sclerotia germination increases once the soil temperature reaches 10ËšC, provided the soil surface is moist. The sclerotia then release air-borne spores around 10-14 days after germination and these infect oilseed rape petals on stems and leaf axils, once night time temperatures are above 7ËšC. Petal fall is the riskiest time for infection.

Jon explains that that oilseed rape is at highest risk when sclerotia germination is synchronised with early flowering. “Extended flowering, high levels of sclerotia in the soil, plus spores travelling over 100 metres from adjacent crops all add up to high risk in most crops. Oilseed rape can flower for 6 to 8 weeks, which is why rape crops regularly receive 2 fungicide sprays. This year many winter oilseed rape crops will be growing on land that will have significant levels of viable sclerotia in the soil. You only need 2 sclerotia /m² to start an epidemic. Disease monitoring helps growers assess risk and decide on the need for and timing of fungicide treatments.”

“Because fungicides are mainly protectant, applications need to be timed correctly, in advance of disease and before any significant petal fall. BASF advise growers to adopt a two-spray strategy,” he says.

“The first spray, applied late green to yellow bud, is Sunorg Pro (metconazole) which will give about 3 weeks early protection against Sclerotinia. Applied 4 to 6 weeks before the main infection period, Sunorg Pro will make a valuable contribution before the main mid flower treatment and gives more effective coverage of the lower canopy, which can be difficult to achieve with a flowering spray.”

“The main mid-flower fungicide treatment of either Filan (boscalid) or Compass (thiophanate-methyl and iprodione), will give between 24 to 28 days persistence, if applied at full rates of use.  In independent trials in high disease years, Compass and particularly Filan performed well in terms of disease control and yield.  In fact these two fungicides were in the top three fungicide performers in these trials. In both trials and in the field, they give reliable and consistent protection against Sclerotinia, as well as broad-spectrum activity against Alternaria and Botrytis. They also offer an alternative mode of action into an overall disease programme that tends to be crowded with triazoles.”

Growers are also advised to use water volumes that ensure spray coverage is good and that enough active ingredient is distributed throughout the petal layer and lower in the canopy, particularly leaf/stem axils where petals stick.

Jon Williams points out that Sclerotinia is a widespread, damaging disease which can substantially erode yields. “Average yield losses are 50% on each affected plant, which means that a crop with 20% Sclerotinia would have a 10% yield loss. Yield response to Sclerotinia control has ranged from 0.5t/ha when disease levels were moderate to 2.0t/ha when disease levels are high. Filan has been shown to produce an average extra yield of 0.25 t/ha even in the absence of disease through its strong physiological effects. In a series of 17 trials across Europe the use of Filan resulted in an average yield response of 0.62 t/ha, valued at nearly £250 at current prices. Filan will be an economically viable treatment whatever the season brings.”