Sowing date vital to oilseed rape variety choice

Care should be taken when choosing an oilseed rape variety to be established before 10 August or after the first week in September, according to Lee Bennett of plant breeders CPB Twyford.

“With wheat we quite clearly put varieties into specific drilling date camps, while oilseed rape tends to get chosen by gross output rather than sowing date.

“But as farms get bigger the sowing campaign will get extended, and if you’re going early [before 10 August] you need a particular variety,” he says.

Typically it needs to have slow development so it doesn’t get too much luxurious early biomass. That will make it easier to manage in the spring, he explains. “The wrong choice would be restored hybrid, or a tall, vigorous variety, such as Winner, for this slot.”

Another key characteristic for early sowing is good resistance to phoma.

“Phoma will likely come in earlier so you need better genetic resistance to give a wider application window.”

It would also be “nice” to have a variety that is later flowering, he suggests. “As soon as you put it into the ground the clock starts ticking for when it will flower. If flowering is triggered early, there is a greater risk of frost damage, and it’s the flowers that drive the number of pods.”

Varieties suited to very early drilling include Komando, Kador and ES Astrid, plus the new semi-dwarf types, he suggests.

In mid-season, from around 10 August to 7 September, variety choice is much less critical. “You can do what you want – most varieties will perform well.”

But sowings later than 7 September require vigour, he stresses. “You’re playing catch-up, and soil temperatures are running out, so this is where hybrid vigour really scores.”

  • For more on how to establish oilseed rape successfully turn to p56 for our Crop Establishment Special.

SEED RATES: less is more
Seed rates for oilseed rape are generally much too high, Mr Bennett says. “Insurance seed rates generally don’t pay.”

In fact his trials have shown less is more. In two trials with the hybrid variety, Trabant, drilling between 30 and 42 seeds / sq m gave the highest yields of around 5t/ha. When seed rates increased to above 50 seeds / sq m yields dropped to around 4.4t/ha.

“At lower seed rates you get better expression of plant type and better branching, which equals more pods, and more yield.”

Typically growers planting hybrids sow 60 seeds/sq m, which costs around £15/ha more than 40 seeds/sq m, he says. Not only that, but because seeds compete against each other, establishment percentage drops when higher seed rates are planted. “Lower seed rates give you better value from your seed.”

But to lower seed rates, establishment must be right, he stresses. “It is only possible in conjunction with having sufficient moisture available, and getting seed structure right.”

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