Controlling Sclerotinia disease in oilseed rape crops will be more important than ever this season, as the UK’s rapeseed area is considerably down, which makes optimising yields of those crops in the ground critical.

Sclerotinia stem rot is a significant disease of oilseed rape in the UK. Sclerotinia prevents movement of water and nutrition through the plant’s vascular system and in some circumstances can reduce yields by 50% or result in complete loss through plant death.

It infects crops in the spring when the fungal ascospores are produced. Oilseed rape crops are at highest risk during warm humid weather when the crop is in flower, as the spores use petals and pollen as a food source in order to develop.

Effective control of the disease relies largely on protectant fungicides that should be applied during mid-flowering before there is any significant petal fall. Ascospores released during sclerotinia germination need a nutrient source, which petals provide, otherwise growers risk yield losses.

The Scottish Farmer: Ruth Stanley, UK and Ireland country manager at Life ScientificRuth Stanley, UK and Ireland country manager at Life Scientific (Image: web)

Ruth Stanley, Life Scientific’s country manager for UK and Ireland, explains how the next few weeks will be vital for growers to control the disease as the majority of crops are coming into flowering.

“Flowering is relatively on track in rapeseed crops this season and will begin in mid-April. Some forward crops are already starting to flower,” she says.

“By spraying during mid-flowering, the peak number of flowers receive the fungicide active, which limits disease spread,” she adds.

“Another challenge with Sclerotinia decisions is that the fungicides only have a protectant role and have to be applied ahead of infection taking place.

“In some years, a prolonged flowering period can also mean that a second spray is required to maintain protection – adding to the crop’s growing costs at a time when all expenditure is being scrutinised and has to be justified.”

She adds: “Sclerotinia is the reason given for almost 30% of total fungicide use in the crop.”

“Against this background, the weather has become less predictable.”

However, Mrs Stanley points out understanding the persistence of fungicides after application is key.

“As Sclerotinia control relies on protectant treatments, it is important to recognise the persistence of control and how this is linked to dose rate, in order to cover the periods, the crop is at most risk from the disease.”

For sclerotinia infection to occur there must be a minimum of 23 consecutive hours of temperatures greater than 7C and a relative humidity of over 80%.

Growers are advised to use the AHDB disease-monitoring service, which maps weather and humidity patterns of specific UK sites.

“It’s absolutely essential growers continue to monitor their crops and keep an eye on weather conditions in order to calculate the impact and timing of Sclerotinia, to limit its spread and avoid yield losses,” says Mrs Stanley.