10 April 1999

Record rape is within reach

Be more professional with rape management, says the UKs leading hybrid rape breeding company. Gilly Johnson reports.

GO FOR yield – thats how to keep oilseed rape worthwhile under Agenda 2000, says Liz Williams, plant breeder with CPB Twyford.

Cutting inputs is a short-sighted strategy, she suggests. "Growers must focus on achieving the full potential from rape – and that requires more professional management, and better targeting of inputs, than many crops are currently receiving."

With a new high yielding composite hybrid rape – Gemini – in the companys portfolio, Ms Williams has an incentive to see rape management move up a gear. The yield potential from this "super varietal association" – a mix of a sterile hybrid plus a fertile hybrid pollinator – goes beyond that of either Synergy or the fully restored types such as Pronto, she says. Gemini is the first of this type of hybrid variety to be commercialised.

Record marks

Teasing out the detail from NIAB data gives an indication of just how far yields might go with these dual hybrid associations. Recommended list yield rating puts Gemini at the top of the new 1999 ranking, just a whisker ahead of Pronto. But the range of yield performance within the figures reveals that some plots were within reach of the 6t/ha (49cwt/acre) mark – a NIAB record for English oilseed rape trials (higher yields have occurred in Scotland). For comparison, the highest English yield for Synergy was 5t/ha (40cwt/acre) and for Pronto 5.2t/ha (42cwt/acre).

One of the top sites was at Framlingham, Suffolk. Why did Gemini do so well here? "First, as a sandy clay loam, the soil type was ideal," says Ms Williams. "But having enough nitrogen is also important if you want to push the crop to its maximum." The site was given high N – 258kgN/ha (205 units/acre), as well as pig manure. Calculations on N removal by a high yielding rape crop would suggest a total need around 300kgN/ha, and fertiliser rate should take into account previous cropping and residual N.

Drilling date, at 10 September, might be considered on the late side, but vigorous hybrids should not be sown too early, or the crop could end up too thick and lush, she suggests. "Ideal drilling date to my mind is about 20 August; dont go before 15 August at any rate. And seedbed conditions are important – the moisture needs to be there. Its better to wait if conditions are not right."

Fungicide inputs

The record-breaking plot had light leaf spot/phoma fungicide (Punch C or flusilazole with carbendazim) as an autumn and spring split. This was followed by a mid-flowering application of Compass (iprodione with thiophanate-methyl). The big yield pay-off justified this level of fungicide input – despite Geminis high resistance ratings, which match the best on the 1999 Recommended List for light leaf spot and downy mildew.

For hybrids, it is critical not to have too high a plant population; vigorous plants need space to show their potential. It would seem safer to err on the side of low plant population than to drill at too high a seed rate. Theres an economic argument too, given the extra cost of hybrid seed (about £20/ha or £8/acre more than conventional).

Hybrid seed is sold in area packs, with the seed number and weight calculated to give a population of 60 plants per square metre. However, for growers able to apply professional management to the crop, seed rate could be trimmed back slightly from the breeders recommended rate without jeopardising yield potential, allows Ms Williams – but only if conditions are right.

With hybrid seed production, rape is sown in wide rows (12-14in) to allow roguing, with about 6-10in space between plants in the row. Even at these low populations, yields are high, which raises the question whether precision drilling of hybrids at low seed rates might be helpful. CPB Twyford is considering the possibility.

&#8226 Currently, one in two rape growers has an area of a winter hybrid variety, according to the companys figures. Its forecasts say that by 2002, the UK area of winter rape will be similar to todays, at approaching 500,000ha, with 60% as hybrid varieties. However, there will be a temporary reaction against the Agenda 2000 cut-backs, causing a 10% decline in winter rape area this autumn.