Why Devon farmer is growing oilseed rape again

Oilseed rape crops across parts of the UK started flowering a month ahead of usual, following favourable autumn weather and mild winter conditions.

For Devon farmer Joe Mawle and his father Jim, crops began flowering on 10 March and were in full flower by the start of April – something the pair wouldn’t usually expect to take place until the end of April or beginning of May.

“Crops are looking well, but I’ve not known them to start flowering this early before,” says Joe. “The flowering period is key to setting yield and we’re a bit worried this could affect yield potential.”.

See also: 10-point plan to beat flea beetle in oilseed rape

Strong crop establishment in the autumn, coupled with reduced cabbage stem flea beetle pressure and a mild winter, meant crops came into spring well developed.

As the warm temperatures hit, plants accelerated through their growth stages from vegetative to stem extension and into flowering.

Although oilseed rape is capable of self-pollination, insect pollinators – especially bees – increase the number of seeds per pod and the number of flowers that successfully set pod. Pollinators can also lead to more uniform pod development.

When flowering happens earlier, pollinator numbers may lag behind and the duration of flowering may be shorter, which limits pollinator activity and consequently yield.

“Temperature, daylight, sunlight and pollinators all have a major impact on oilseed rape yield and the trouble with too-early flowering is that this can all get out of sync,” explains Jim who is Basis and Facts qualified and looks after the farm’s agronomy.

“The potential is there, crops are looking exceptional, we just hope the early flowering won’t cause too much of an issue. It’s so hard to judge OSR yield before you’re in the field with a combine. We just need good weather now to set the seed well,” he says.

Return to OSR

After a few years’ break from the crop, Joe and Jim are back growing oilseed rape for the second year running now that market conditions have improved.

The crop was reintroduced in replace of a significant area of winter oats which have experienced a considerable dip in the market. Currently, 50ha of rapeseed is being grown at the family farm on the edge of Dartmoor.

“Oilseed rape was undervalued. People weren’t growing it as much so we thought now was a good time to get back into it. Oats are a more reliable break crop to grow but markets have been knocked and rapeseed offers the better margins now the oil price is high,” says Joe.

© Emma Gillbard

This year’s crop

This year’s crop was drilled at the end of August, with Joe noting he was relieved crops weren’t sown earlier given how mild the autumn and winter have been. Last year‘s crop was drilled at a similar timing but flowered as normal.

“If we’d have drilled earlier, crops could have been flowering in January,” he jokes, reflecting on how rapidly the crop has developed this season.

“Our cut-off for drilling is 10 September, otherwise crops struggle to get going as we are in quite an exposed location being so close to Dartmoor,” says Joe.

This year crops were put into extremely warm and dry seed-beds, which is likely to have accelerated development and contributed to early flowering.

“We rolled ahead of drilling to conserve moisture, and thankfully it rained a couple of days after drilling,” says Joe.

Pest management

Establishment starts with sewage sludge applied to winter barley stubble, for a dose of early nutrition. The sludge also acts as a major flea beetle deterrent due to its unattractive aroma.

The pass of a Sumo subsoiler is used to incorporate it before drilling with either a Horsch Pronto or Claydon drill. The pair opt for both hybrid and conventional varieties – hybrid Maverick is looking particularly well this season.

© Emma Gillbard

Slugs remain one of the biggest ongoing challenges. Joe reports the first two weeks after drilling to had particularly high slug pressure.

“We had to apply slug pellets and after that the crop turned a corner and it has grown full bore ever since,” he says.

Jim notes that by the end of February crops already had a green area index (GAI) of 2.5, so they went in with a plant growth regulator to hold growth back a little and manage canopy height.

When it comes to cabbage stem flea beetle management, the pair ensure crops have adequate early nutrition to get them up and away.

“Getting nutrition in place early is essential to help the crop establish quickly and withstand pressure from pests through the autumn,” says Joe.

As a result, cabbage stem flea beetle has never completely wiped out a crop on their farm. Regular night-time monitoring with a headtorch is used to assess pest levels.

“We monitor crops accordingly. If there is an issue, we tend to walk away and let nature sort it out,” says Jim. Believing strong establishment to be the most important pest defence, he aims to get crops quickly to the two- to three-leaf stage.

Exposed Dartmoor location

Disease and canopy management is important given the farm’s high rainfall near Dartmoor. That’s why a two-spray fungicide approach is deployed.

The typical windy conditions of Dartmoor make a pod stick application at harvest essential to reduce losses from pod shatter.

Harvest management also includes desiccating crops with glyphosate ahead of combining. Straw is then baled and sold as bedding, which removes residue from the field, helping reduce slug pressure.

The farm rotation is diverse. Winter wheat, winter barley, winter oats, beans, grass and maize for a local dairy sit alongside Sustainable Farming Incentive options including herbal leys and wild bird food mixes on awkward field corners.

Last year was a great one for oilseed rape at the farm. The crop achieved a yield of 4t/ha, supported by good sunlight during grain fill.

A bonus of about £55/t linked to oil content and moisture performance peaked at roughly 4.5t/ha.

While the current crop is looking strong, both Joe and Jim remain cautious the unusually early flowering could influence final yield outcomes.

In what has otherwise been a promising season, the key now is prolonging flowering and having a good period of weather to set seed and allow the crop to maximise yield as much as possible.