OSR stem-based diseases – don’t overlook the damage

Arable OSR stem-based diseases – don’t overlook the damage

As the British climate trend moves towards warmer wetter weather, the risk to oilseed rape crops from the diseases of light leaf spot, phoma and verticillium stem stripe also increases. All three diseases can have a serious impact on oilseed rape yields and oil quality, warns plant breeder Limagrain UK.

“With oilseed rape prices up at £700/t in late March, 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. A at crop is of no use to anyone,” says Liam Wilkinson (pictured), arable technical o cer for Limagrain UK.

“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.”

He points out that whilst phoma and verticillium are generally well recognised stembased diseases, the signi cance of their impact on UK OSR crops could be questioned.

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

Mr Wilkinson considers light leaf spot (LLS) to be the biggest OSR disease threat in the UK, and says it is increasingly harder to control.

“Light leaf spot used to be considered to be a disease of the north – but this is no longer the case, as mutations and a reduction in azole e cacy, alongside milder winter weather, have resulted in it spreading across the UK, with yield losses of up to 1t/ha.” “Often only considered to be a disease of the canopy, LLS infection can spread to the stem – resulting in serious issues from stem distortion, stunting, poor pod formation and oil quality issues, and is often overlooked.”

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 o er 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,” he says.

“Varieties with similar light leaf scores on the AHDB RL will, in reality, have very di erent stem

Establishment survey throws light on importance of drilling conditions for OSR success

Strong prices and good autumn establishment has renewed con dence in oilseed rape as many growers consider a return to the crop in 2022, says Will Charlton, arable marketing manager for Limagrain UK.

To support growers and help to mitigate the nancial impact of a crop failing to establish, in 2021 Limagrain worked closely with partners in the seed trade to set up an Establishment Scheme.

“The scheme accounted for 19,000ha of OSR planted in 2021, representing 8.3% of the total hybrid area and 6.2% of the total certi ed area so a signi cant area of the rape in the ground,” says Mr Charlton.

“This has provided us with an extremely useful insight into when crops are drilled which we have been able to track against weather at the time.

“Most of the OSR in 2021 was drilled in the rst two weeks of August – much earlier than it had been before the neonicotinoid ban, when the typical drilling date was the third week of August.”

He points out that when plotted against the weather, the data showed that where drilling was carried out in dry conditions, subsequent crop loss was closely correlated.

“However, where there was rainfall on or around the two weeks from drilling, plant survival was much more likely.

“This data reinforces the need for moisture when drilling oilseed rape for successful establishment as this allows the crop to germinate and grow up and away from CSFB as quickly as possible,” he adds.

Mr Charlton’s advice is to drill for conditions, not calendar date and choose a variety with adaptability that can cope with this. For example, a very vigorous hybrid such as LG Aviron, LG Antigua, Ambassador or Aurelia gives growers the exibility to wait for the right conditions.

There are several agronomic practices that can help mitigate CSFB damage, points out Mr Charlton. “These are all based on increasing branching to minimise larval damage,” he says.

“Seed rate is key – if the crop is too thick, it reduces the plant’s ability to branch out and the beetles head for the main stem, where emerging larvae cause the most damage. However, in a well branched out plant, the larvae spread out to the side branches and the plant can cope much better.

“An e ective autumn and spring PGR programme will also help to manipulate branching, and minimise damage from CSFB larvae,” Mr Charlton adds. health scores.

“So incidences of stem infection often go unreported, resulting in unnecessary yield and quality reductions.”

All of the varieties currently on the RL have been scored for cylindrosporium in Limagrain’s own trials, as well as for LLS in the RL programme. To illustrate this, Mr Wilkinson refers to Limagrain trials carried out in 2020.

“We evaluated the stem health of several varieties that all held the same light leaf spot score of 7 on the AHDB RL (1 being clean, through to 9 which was fully diseased).” (See Graph below).

Severity Score (1: clean; 9: diseased)

9 8 7 6 5 4 3 2 1 0 UK Site

RL Score: 7 RL Score: 6 RL Score: 6 RL Score: 7

AURELIAAMBASSADOR LG AVIRON Comparator Hybrid RL LLS Score 6Comparator Hybrid RL LLS Score 7Comparator Conv RL LLS Score 6

“Aurelia was given an excellent score of 2 for overall stem health; Ambassador and LG Aviron scored a very good 3, but one variety only scored a 6 despite also holding a light leaf spot rating of 7.

“The important message here is to look behind the headline scores and don’t assume that a good overall light leaf spot score translates into a good stem health score.

“The next generation of Limagrain lines are looking really clean for all the major stem-health diseases. These will begin to appear on the UK market this autumn, and will be more widely available in 2023,” concludes Mr Wilkinson. FG