Fungicide application timing and control of Sclerotinia stem rot in England in 2007 and 2008

Abstract: Stem rot (Sclerotinia sclerotiorum) on winter oilseed rape has caused significant yield losses in the UK in 2007 and 2008. Industry-funded trials in the West Midlands investigated the effect of fungicides on stem rot control in 2007 and 2008. These trials demonstrated that the onset of infection and fungicide application timing to be significant factors in stem rot control in oilseed rape. In 2007, initial infection occurred in late April/early May whereas infection occurred in mid to late May in 2008. Fungicides applied in late April gave good early control of the epidemic in 2007. In contrast, in 2008, fungicides applied in late April did not control the epidemic as effectively as those applied in early May due to the later onset of the epidemic. In both years, the control of stem rot infection declined as the season progressed following a single mid-flower fungicide application. Strong fungicide protection persisted for about three weeks. The significance of these results on Sclerotinia control is discussed.