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• Drilling date has bigger role to play • Milder winters affecting rape yields • Growth regulator can reduce losses Applying a plant growth... Plant growth regulator rewrites rules on rape

• Drilling date has bigger role to play

• Milder winters affecting rape yields

• Growth regulator can reduce losses

Applying a plant growth regulator (PGR) to early drilled oilseed rape could hold the key to better yields, say experts.

Genetic improvements are giving higher yields in trials. But this isn’t translating to the field – possibly due to what industry leaders believe is a combination of milder winters, earlier drilling and crop physiology.

Only 8% of British growers currently use a PGR on autumn oilseed rape. But more should do so, says Chris Guest, managing director of plant breeder NPZ UK, who is calling for a mindset change.

Changing climate

“Growers used to start drilling at the end of August but we have seen a huge shift in drilling date, with 75% of oilseed rape now drilled-up by the middle of the month,” says Mr Guest.

Forward crops are better able to withstand adult cabbage stem flea beetle (CSFB) damage – but these crops are prone to another yield-limiting challenge, he adds.

“Growers are often frustrated that they aren’t getting the yields we see in trials. This is largely about drilling date – oilseed rape in trials tends to be sown over a month after those in the field.”

Oilseed rape plants start to develop flower buds and side shoots once they have six leaves. But this ‘bud and root’ phase stops and crops enter a phase of ‘reduction’ at the 12-leaf stage.

Bud and root differentiation usually starts in October and ends at the beginning of March. But it can be over by January in warmer winters, suggests research by Ute Krupf, of the University of Applied Sciences in Kiel, Germany.

“This, in turn, has pushed flowering forwards into months where they are prone to frost damage – with detrimental impact on seed quantity and therefore yield,” explains Mr Guest.

This could partly explain why oilseed rape crops grown during the colder winters of 2008-2014 regularly yielded 5-6t/ha, while those grown during the warmer winters of 2015-2023 have recorded much lower yields.

“With milder weather and the lack of winter shutdown, these forward rape crops are racing through those growth stages that determine yield potential quicker,” says Mr Guest. “It could be limiting yields by up to 30%.”

Reducing losses

Applying the research in the field in the UK and across Europe, NPZ has shown that autumn PGR applications hold back crops, giving them more time to create more buds and consequently, more pods and seeds.

“With the changes in climate, an autumn PGR is well worth considering, but for those earlier drilled crops that are reaching the relevant growth stages, it’s arguably essential,” adds Mr Guest..

The only PGR authorised for autumn use is Caryx, which is manufactured by BASF. Getting the best from the product is all about timing, says BASF business development manager Clare Tucker.

“This year, early drilled rape has had a good start and many will reach four to six leaves by mid-October or before,” she says.

“Those sown at low seed rates will have space around them but any populations of 35-40 plants/m2 or more will grow tall quickly, with weak lower stems, making them more vulnerable to flea beetle larvae damage and lodging in spring.”

When to apply

Ms Tucker recommends the use of Caryx for any crops reaching four to six leaves in September or by mid-October. It may be necessary to do further canopy management in the spring, she adds.

“Timing is crucial. Plants larger than four to six leaves will be too big to benefit fully, so don’t delay applications. Growth starts to slow down by late October and PGR activity will be much less.”

As well as preserving yield potential, autumn applications of Caryx reduce lodging risk and increase resilience to CSFB larvae feeding damage.”

Restricting the upward plant growth also improves large root collar diameter and helps plants better withstand damage from cold and wet soils.

ADAS head of crop physiology Pete Berry agrees: “Waiting until you’ve got eight or nine leaves is definitely going to be less beneficial.”