Consider using companion crops for winter oilseed rape

This is not just to limit cabbage stem flea beetle (CSFB) damage, but also to unlock the Government’s new Sustainable Farming Incentive (SFI) payment, says Mike Thornton, head of crop production for agronomy firm, ProCam, who emphasises that growers must consider several important factors before rushing in.

Mr Thornton says: “Using the correct companion crop or blend of crops has clear agronomic benefits when trying to establish a new crop of oilseed rape.

"In addition to improving soil structure and reducing weed pressure, species such as buckwheat and fenugreek can also reduce insect damage by masking the developing OSR canopy from problem pests including the troublesome cabbage stem flea beetle.

“And with Defra offering growers an incentive of £55/ha to grow a companion crop alongside arable crops, plus another £45/ha for not using insecticides, the cost of purchasing and establishing the companion crop is negligible, if not completely covered.”

Mr Thornton explains that the ideal companion crop will enhance OSR establishment and protect against CSFB infestation, before being killed off naturally by frosts.

He says: “In doing so, the companion crop won’t interfere with or compete against the developing OSR plants as they continue to develop through the winter and into early spring, and won’t incur any costly or timely mechanical or chemical crop destruction charges.”

In terms of companion crop species selection, Mr Thornton advises that it is important to choose varieties suited for planting alongside OSR and to ensure that the chosen seed is of a high quality to maximise germination rates.

“Companion cropping is beneficial for a number of reasons including soil enhancement, pest deterrence and weed suppression, but it is important to ensure the correct type and quality of seed is used to attain these benefits,” Mr Thornton explains.

“To make seed selection simpler, ProCam offers three companion crop mixtures with various ratios of three carefully selected varieties of buckwheat, fenugreek and Berseem clover, all of which have been chosen to give growers flexibility depending on their individual needs and cropping circumstances.

Mike Thornton of ProCam

“For example, our ‘Shielder’ mixture contains 50 per cent buckwheat (Lifago), 25 per cent berseem clover (Tabor) and 25 per cent fenugreek, all of which play a specific role in boosting OSR establishment.

“Lifago boasts a smaller seed size than standard buckwheat so that it produces a high population of plants. It also makes drilling easier as the buckwheat seed is of a similar size to OSR seed so the two can be mixed and drilled together.”

The dense canopy that Lifago produces hides and protects the developing oilseed plants from flea beetles, as well as improving phosphate mobilisation within the soil. “And because it is susceptible to frosts, Lifago breaks down naturally in the winter to reduce crop competition,” Mr Thornton adds.

For the Berseem clover element, Tabor – the only single-cut variety available in the UK – has been chosen. “This too is easily killed by frost,” Mr Thornton explains, “and doesn’t subsequently regrow. Its main advantage is to improve species diversity within the crop and to promote improvements in soil biology and conditioning.”

The third element of the Shielder mixture, fenugreek, emits a natural garlic-type odour that deters pests later into the autumn for prolonged defence against cabbage stem flea beetle.

Mr Thornton recommends that where soil moisture is plentiful the companion crop should be sown at the same time as the commercial OSR crop.

He says: “However, in a dry year where soil moisture is lacking and could impact oilseed establishment, the companion seed should be sown in advance, with the OSR seed introduced once sufficient soil moisture is available.”

Mr Thornton also urges growers to think carefully about weed control options.

He says: “Pre-emergence herbicide applications won’t be possible as these have the potential to kill the companion crop. However, a wider range of post-emergence options such as propyzamide, halauxifen-methyl, picloram, and the Clearfield system can be used, but these shouldn’t be applied too soon as early application could diminish the value delivered by the companion crop.

"The best advice, where feasible, is to wait until the first frost has killed off the companion crop naturally.”

Ultimately, the decision of whether or not to grow a companion crop comes down to growers identifying their biggest priority when trying to establish a new crop of oilseed rape, says Mr Thornton. “If the primary objective is to improve soil condition and reduce cabbage stem flea beetle damage, a companion crop is a good option. On the other hand, if the main goal is weed control, it might be more sensible to grow OSR without a companion crop as this will ensure greater flexibility in terms of herbicide choice.”