12 May 1999
Spraying oilseed rape for Sclerotinia
WHAT are your thoughts on Sclerotinia spraying in rape, bearing in mind the rapeseed price this year?
Dr Joanne Liggitt, Fungicide Development Manager, Cyanamid Agriculture UK
ITS not often the UK sees a bad outbreak of sclerotinia – 1991 was the last
epidemic – but when it strikes, it can be particularly vicious, reducing yield
within a crop by between 5-10%, or in extreme cases causing total crop failure.
The question being addressed is whether its worth taking the risk of infection.
Unless the price drops to quite disastrous levels, my advice is “ignore that
risk at your peril”. Indications so far this year suggest that, across the country, the risk is higher than average. Wet weather, early flowering and the
present warmer temperatures have increased the risk markedly.
Furthermore, due to the nature of rotations, many crops of oilseed rape are this year being grown in fields that contained rape during the last sclerotinia outbreak. Also, the apothecia, the fungus fruiting bodies, can survive for up to eight years in the soil.
The combination of all these factors suggests that 1999 is a high-risk year.
There are a few options available to growers.
If wheat and rape are being grown in roughly equal proportions on a farm, then a routine spray is advisable and an mbc alone should suffice.
Where more than 20% of plants within a field in the farm have been affected in recent years, then let the presence of apothecia alert you to the need to spray, either using an azole+mbc or dicarboximide+mbc.
Ongoing development trials with ACF474, Cyanamids new triazole, have
demonstrated exemplary control of the disease. Subject to approval, this will
become available next year, giving oilseed rape growers a new control option.