Spray for sclerotinia in oilseed rape as soon as possible as risk increases

Oilseed rape crops will need spraying as soon as opportunity allows as sclerotinia pressure increases, Peter Gladders of ADAS warns. In high-risk situations two sprays are almost certain to be justified.

“We’re seeing germination increasing week on week, so the pressure will likely be increasing,” he reports.

Results from ADAS / BASF monitoring (www.totaloilseedcare.co.uk) show 6% germination at Boxworth in Cambridgeshire, and 9% at Terrington. Germination has yet to start at High Mowthorpe. Soil temperatures of over 10C and a bit of soil moisture are ideal for germination, he says. “We’re just about there for soil temperatures.”

Apothecia have been found in winter wheat crops after oilseed rape crops in the Thames Valley area, he reports. “It is now a good time to look for apothecia in winter cereal crops where there has been a history of sclerotinia. Sclerotinia spores are likely to be able to spread from infested cereal fields to nearby oilseed rape fields. Finding apothecia nearby would justify fungicide treatment.”

Oilseed rape crops are under increasing threat from sclerotinia, Peter Gladders of ADAS says

The first petal tests indicate that sclerotinia ascospores have been produced for at least three weeks, and some crops are already at risk despite relatively low germination. Crops in the Hereford area, for example, results suggest high levels of sclerotinia (35-65% petals affected) are present and fungicide treatment is required.

“In previous years 25% petal infection has resulted in significant sclerotinia stem infections.”

Risk is likely to increase as soil temperatures rise. “Crops at early to mid flowering should be treated where there is considered a risk. Fungicides give about three weeks protection and a second fungicide treatment may be justified this season at high risks sites because of high crop value.”

There are a number of products growers could use, he says. “The front runners are Filan, Proline and Compass, but our trials showed most are good as long as you keep rates robust.”

Growers in northern regions where light leaf spot is also an issue will need to choose a product with a triazole component, such as prothioconazole or tebuconazole, he adds.

Active ingredients]

• Filan – boscalid
• Proline – prothioconazole
• Compass – iprodione + thiophanate-methyl

Sclerotinia advice

• Infection risk growing
• First sprays required ASAP
• Check again three weeks after spray
• Two sprays could be justified