‘Hidden threat’ posed by disease to oilseed rape

Damage caused by stem-based diseases in oilseed rape must not be ignored, warn UK plant breeders.

As the climate becomes warmer and wetter, rape is at higher risk of light leaf spot, phoma and verticillium stem stripe. All three diseases can seriously reduce yields and oil quality – causing hefty losses at a time when rape is worth more about £800/t.

“It’s crucial to keep the plant as healthy as possible if it has any chance of reaching its full yield potential – and this includes the health of the stem,” says Liam Wilkinson, arable technical officer for Limagrain UK.

Harder to control

“A flat crop is of no use to anyone. Over the last few years there has been much focus on canopy health in oilseed rape, but stem health is an area that is often overlooked and can have a serious impact on gross output.”

While phoma and Verticillium are generally well recognised stem-based diseases, Mr Wilkinson considers light leaf spot to be the biggest disease threat – warning that it is increasingly harder to control.

“In recent years, phoma has become less of a problem with the use of resistant varieties,” he explains. “Verticillium stem stripe is a more sporadic disease, more closely linked to region, weather and crop factors.

“Light leaf spot used to be considered to be a disease of the north, but this is no longer the case. Mutations and a reduction in azole efficacy, alongside milder winter weather, have resulted in it spreading across the UK, with yield losses of up to 1 t/ha.”

Often only considered to be a disease of the canopy, light leaf spot infection can spread to the stem resulting in serious issues from stem distortion, stunting, poor pod formation and oil quality issues. These are often overlooked, says Mr Wilkinson.

Cylindrosporium is the stem-based stage of light leaf spot, a disease caused by the pathogen Pyrenopeziza brassicae. LLS is a polycyclic disease, producing more than one infection cycle per season, and Cylindrosporium concentricum is its asexual stage.

“Varieties offer good light leaf disease resistance ratings on the RL, but it’s important to recognise that in the UK, light leaf spot on the stem is not something that is scored for in the AHDB RL, it’s only the leaves that are scored for disease.”