What to consider before replacing OSR with a specialist crop

Farmers looking to reduce their oilseed rape area by growing specialist crops should consider the wider impact of their cropping changes to avoid potential new weed, disease and pest problems in the years ahead.

A good example is wireworm damage in potatoes resulting from the introduction of herbage seeds into the rotation.

There are also key practical considerations like having the right equipment and meeting market specs.

See also: Is bruchid beetle making spring beans less attractive? 

Over the coming weeks, many farmers across the UK will consider the future of oilseed rape in their rotations because of crop failures resulting from cabbage stem flea beetle attacks. But the challenge is what to grow instead.

Spring barley and beans are obvious options, but they do not offer the same returns and also have their own problems.

One solution is to grow a specialist premium crop, as they can offer high returns.

Wider OSR benefits

But before looking at the options, NIAB’s break crop specialist Colin Peters believes growers should first fully consider the implications of dropping oilseed rape. There is a value of having OSR in the rotation.

“For example, its removal could have an impact on first wheat yields, due to being a true take-all break and its timeliness in getting the next crop in,” he says.

It may, therefore, be a case of reducing the OSR area rather than abandoning the crop altogether. Widening the rotation by adding a specialist crop may also help ease the flea beetle pressure.

Close-up view of a trailled drill

© Tim Scrivener

Whatever farmers decide, he believes growers need to get back to the fundamentals of thinking what they want to get out of their rotations.

This summer is a good time to review rotations, as many farms have already been forced to make changes with less winter wheat and some fields being fallowed.

He advises that growers start by considering what crops they can grow profitably and then design the rotation around them. This will then give an idea of what type of break crops are needed.


Another key consideration is the market, and growers should ideally have a contract in place before growing a specialist crop – especially as these markets can easily be oversupplied.

Mr Peters pointed out that a key difference with such crops, unlike wheat, is that they are not commodities. Farmers are selling into a very different market, often much closer to the end of the food chain.

“Growers need to understand what the customer wants. If it doesn’t make the spec, it is not just a case of losing a few £/t like with wheat. They may not want it at all.”

Andrew Probert, managing director at Premium Crops, agrees that meeting quality specs is vital. “These specialist crops are often displacing imports, so quality is paramount. Canary seed is a good example and buyers want whole seed with no straw or ergot.”


Moving to agronomy, growers should consider how the crop affects weed control. “Does it fit in with your blackgrass control strategy?” said Mr Peters.

Don’t forget that there may be limited herbicide options and products are often used under extensions of authorisation for minor use. “So it’s worth checking what’s available and if there are any limitations.”

Mr Peters also warned about introducing volunteer weed problems. For OSR/cereal rotations, there really isn’t a problem with crops such as borage.

“But if there is sugar beet, potatoes or carrots in the rotation, you can easily introduce a problem that you will see two or three years down the line,” he said.

“A good example is volunteer borage in sugar beet or potatoes.”

Sugar beet is running out of herbicides, so farmers have to be careful, especially as seed can last for years in soil.

“And we no longer have Reglone (diquat) in potatoes, so they will be more difficult to manage. It’s going to take two or three years to get our head around what [loss of Reglone] means, so farmers need to be wary.”

Pests and diseases

Bringing the wrong specialist crop into the rotation can also inadvertently create a new pest or disease problem.

He again points to farmers with potatoes in their rotation, as introducing herbage seed crops could lead to a wireworm problem, especially as we no longer have chlorpyrifos.

“In the past we could have glyphosated off grass and used chlorpyrifos to manage wireworms, enabling potatoes to be grown without much of a problem.”

But it is now a challenge and something to be aware of.

Similarly, farmers may have grown the crop in the past without any issues, but loss of products mean it may have changed.

Another example is the fungal disease take-all. “Is the crop a true take-all break? That’s something oilseed rape does offer.”

There are benefits too. For example, pigeons don’t like borage so it can be an option in areas where some other crops would get grazed off.

Labour and equipment

On a practical level, does the crop require specialist equipment? For example, borage needs swathing and it needs doing at the right time. Other crops such as quinoa may require inter-row spraying or cultivation for weed control.

For crops with fine seed including quinoa, farmers may need to dry them to a lower moisture level than are used to with standard crops. Also diesel fumes are not acceptable and, therefore, they need careful drying with clean air.

Quinoa plant

Crops with small seed, such as quinoa, may need specialised drying equipment © Tim Scrivener

He warned that some crops might not dry with a conventional dryer and require specialist equipment.

Soil health

Herbage seed crops and grass leys are useful for improving soil health as they provide organic matter to soils.

Conversely, crops that require early drilling in spring may not suit the soil type and risk damage.

“Maize for biofuel can damage soil structure if farmers get it wrong,” he said.

NIAB is set to publish a new booklet, Alternative Break Crops, this summer and members will also be able to download PDF guides for each specialist crop option.

Specialist cropping checklist: NIAB’s 7 factors to consider

• Market
• Site suitability
• Weed problems
• Pests and diseases
• Financial
• Labour, timeliness and equipment
• Take an experimental approach

Don’t forget biomass and energy crops

Short rotation willow coppice and miscanthus are specialist crop options that may prove attractive for growers with biomass boilers.

They tend to be much longer-term options, which Kevin Lindegaard of Crops for Energy said should ideally be grown for at least 20 years.

Willow performs better in the West and is typically harvested every 2-4 years and yields about 8.5-17t/ha a year of boiler woodchip.

In contrast, miscanthus yields better in the drier East, yielding 9-15t at 16% moisture. It is harvested every year.

Both options produce biomass for less than 2p/kWh, about half the cost of buying in wood chips for biomass boilers and he believes this is where farmers can see the most benefit.

Miscanthus could be useful in areas where there was a bad blackgrass problem, he added.

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