YIELD remains the main reason for choosing an oilseed rape variety, but growers should take note of different growth habits to fine tune performance.
So says Simon Kightley, oilseeds specialist at NIAB. "We always see an immediate and wholesale uptake of top yielders. There is no particular allegiance to any one variety."
But soil type and aspect can make a big difference to performance, he notes.
Short, stiff-strawed types like Apex, the top yielder on the NIAB list, Rocket and provisionally-recommended moderate yielder Inca suit heavy, fertile soils or wetter, exposed areas where early lodging is likely to be a problem with taller types. While ideal for direct combining in wet climates, their stiffness makes them prone to shedding, he warns.
"Their short, erect canopy rattles in the breeze. It may be advisable to swath, especially if harvest is likely to be delayed."
At the opposite extreme are tall, weak-stemmed varieties. These are likely to yield more consistently on lighter, drought-prone soils, says Mr Kightley.
Alaska is up for recommendation this year thanks to promising untreated yields. Nickel is also good on disease (provisionally rated 9 for light leaf spot resistance) and has Apex-like yields. Envol is susceptible to light leaf spot and produces moderate yields. Mandarin has performed less well recently, and is recommended in central and southern regions only.
Wet and windy
"In a windy, wet spring these types can lodge severely during flowering. But if they survive that hurdle, they are likely to get to harvest as a low-lying, matted canopy offering considerable resistance to wind shatter."
That makes them a better bet for direct combining, although their growth habit will slow progress. They can be swathed if they are not too lodged, he adds.
Intermediate varieties with moderate standing ability widen the choice. Amber has the same light leaf spot rating as Nickel, and Apex-like yields. Falcon also resists the disease well, which combined with earliness makes it a good choice for the north.
Bristol has been hit by light leaf spot in the last two seasons, but still yields well where disease is controlled. Synergy and Lizard are two list candidates showing particular promise in this category, says Mr Kightley.
Growers should make the most of a "highly adaptable" crop. "There is certainly something to be said for growing a range of varieties on a farm to spread risks."
Seasonal variations affect growth, and who can tell what harvest will be like?"
Short and stiff varieties are easy to combine direct and suit wet areas. But exposed crops are prone to wind shatter and may need swathing.