Oilseed rape growers should assess crops for the risk of Sclerotinia and be prepared to apply a protectant fungicide, experts have advised.

According to BASF/ADAS monitoring, sclerotia germination started during week commencing 3 April, which is similar to previous years, but disease risk will be influenced by several key factors over the coming weeks.

Weather at the start of flowering plays a key part, explained ADAS’s Peter Gladders. “If it is wet at this time, aerial spore release is encouraged and the risk of petal stick increases too. Petal stick is essential for disease development as petals carry the inoculum and provide a nutrient source.”

Light rain provides the best conditions for petal sticking and because most fungicides are protectant, it is important sprays are applied early (early-mid flowering) – especially if weather is unsettled or workloads are high, he says.

Disease risk could also be increased by tighter rotations of susceptible crops – such as peas, potatoes, carrots and brassicas – and minimum tillage, he adds.

“The sclerotia or resting bodies of the pathogen can remain in the soil for many years. Shorter rotations and minimal tillage leaving sclerotia near the soil surface will also mean more disease inoculum and increased disease risk in subsequent, neighbouring crops.”

ADAS and BASF provide weekly Sclerotinia monitoring reports, available at www.totaloilseedcare.co.uk and www.agricentre.co.uk. The reports track sclerotia germination in each region, to help growers assess the disease risk and need for fungicide treatment.