OSR variety choice underpins IPM approach to clubroot risk management

Nineteen lines on a crop management activity report chart the progress of Rob Morgan’s harvest 2025 field scale oilseed rape trials through the all-important establishment and spring restart phases.

From manure spreading on September 15 and drilling on September 18, to an application of growth regulator and a foliar fertiliser on March 27, each pass with the cultivator, drill, spreader and sprayer is carefully recorded

This season close to eight hectares of Rob’s 25ha of oilseed rape at Home Farm, Acton Burnell in south Shropshire is given over to a strip trial conducted in conjunction with Bayer.

There are 10 varieties in the trial on the farm’s medium loam soils, including Bayer’s top performing DEKALB 2024 hybrid newcomer DK Excentric, alongside tried and tested DK Excited and DK Exstar, plus several pipeline hybrid varieties.

The strip trials give Rob a unique insight into the performance of new oilseed rape genetics under his own farm conditions and management regime, something that he particularly values since discovering clubroot on the farm close to 10 years ago.

He believes the disease originated in a two-acre area of game cover planted over several seasons for a local shoot.

“It was there for three or four years on the run and included kale and Utopia (a kale/mustard hybrid),” recalls Rob.

“When the shoot finished, we put the cover area back into the field and the first year we grew oilseed rape on it, we could see a square exactly where the cover crop had been.

“We were expecting that ground to be really fertile because it had had nothing taken off it for four years, but the rape was dying.

“When we pulled up some plants, sure enough, we could see symptoms of clubroot, so we put a drone up, and you could see the affected area as clear as anything in the drone shots,” says Rob.

With oilseed rape providing an essential break crop in the farm’s rotation, Rob, along with his brother Dai, who is an agronomist, decided the way forward was to grow clubroot resistant varieties.

Acknowledging these varieties’ lower yield ratings compared to mainstream hybrids, he points to the crop losses suffered by susceptible varieties when clubroot is present.

“Clubroot can wipe out up to 50% of your crop, so we thought, well, a 10% yield reduction isn't too bad in that case, and now we tend to stick with clubroot varieties,” he says.

Growing wheat/wheat/rape, he accepts that OSR one year in three is nowadays seen as a tight rotation, but farming the 100ha family farm as a one-man operation means his focus is on keeping things simple – as well as economically viable.

Alternative break crops have been considered, from traditional field beans to more exotic lupins, but none have stacked up financially against OSR, or fit as easily into Rob’s farming system.

“I don't want to let land out for potatoes or maize, because I've got the equipment to grow oilseed rape in my shed, and I can do the work myself,” he adds.

“Oilseed rape is probably still the most profitable break crop I can grow at the moment. It would be nice to grow something else, but grain storage-wise I haven't got separate sheds and so we just grow milling wheat and oilseed rape,” says Rob.

Since discovering clubroot on the farm, he has worked hard to prevent its spread, alongside developing an IPM-based approach to crop management to help limit the impact of the disease.

Clubroot resistant varieties top his list of tools, with variety choice strongly influenced by his observations in the farm strip trials. This season one of his three fields of oilseed rape is down to DK Pledge, which was among the top performers in the strip trials last harvest.

“We had DK Pledge in the strip trial last year, and when we harvested it, it was one of the top yielding of all the varieties,” says Rob.

Good hygiene is also important, with machinery cleaned down between fields to prevent clubroot spread, he adds.

“I try to keep machines clean because basically, there's nothing you can do about clubroot once you've got it in soil, other than giving the field a break for 10 years - possibly longer,” he says.

The farm’s oilseed rape is drilled late – never before September 1 – in a bid to minimise cabbage stem flea beetle damage but also to limit the clubroot infection window.

Rob uses a min-till establishment approach – after an application of biosolids, land going into OSR is cultivated with a Sumo Trio combination cultivator, followed directly with a Kverneland e-drill.

“We try and use biosolids before the rape and also apply variable rate Limex on the rape fields before planting and variable rate P and K,” says Rob.

The crop’s sulphur requirement is provided by 185kg/ha polysulphate, which enables the use of variable rate straight nitrogen, applied with a Kuhn Axera spreader.

Cover cropping is an important part of Rob’s overall agronomy approach, with benefits seen in terms of soil structure and carbon capture, but care is needed with cover crop choice, he says.

“We try and grow a cover crop between first and second wheat. After we harvest the first wheat, we plant oil radish as soon as we can and then plant the second wheat in the second or third week of October.

“I use oil radish as my summer cover crop because it’s not affected by clubroot. I was originally planning to plant mustard, because that's cheap and quick to get going, but it carries clubroot.”

To date, Rob’s clubroot management strategy appears to be working. There has been no sign of the disease as oilseed rape has rotated around other fields on the farm, nor was it found this spring in testing conducted by ADAS.

“The field that had the clubroot will be going into oilseed rape this autumn and we will put a clubroot resistant variety on there,” says Rob.

While he is yet to finalise his variety choice, he is interested to see how the pipeline DEKALB variety DMH 585 performs in this season’s strip trials on the farm.

Looking clean, compact and very even in mid-April, DMH 585 combines clubroot resistance with resistance to TuYV and shows similar vigour to that shown by DK Pledge, says Bayer national trials manager Richard Williams, who commends Rob’s IPM approach to clubroot management and attention to detail.

“Rob drills late, he looks after his soil health with liming which can reduce clubroot infections; he controls cruciferous weeds that are hosts to clubroot and he continues to get good yields,” says Richard.

Walking through the strip trial at Home Farm, Rob remarks that the oilseed rape is looking better this spring than it did last and is hopeful of achieving his 4-4.5t/ha average yield target.

He is pleased to hear that Bayer has clubroot-resistant material in its development pipeline and as an enthusiastic triallist looks forward to the potential of stacked traits in the coming years.

“We could do with a Clearfield clubroot resistant variety, then we could simplify our weed control too,” says Rob

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