Winter oilseed rape (WOSR) is characterised by the crop’s ability to develop sufficient canopy from a relatively low plant count.
This is provided the plants are evenly distributed and not excessively grazed by pigeons.
The optimum sowing interval for WOSR crops extends from mid-August (north) to early- September (south), although later sow dates can still deliver good crops.
These sowing dates can clash with harvest activities, making rapid and labour-saving establishment systems attractive.
Establishment of winter oilseed rape
While for best establishment the small rape seed ideally needs a fine, firm seedbed with good moisture conservation and a shallow sowing depth, good crops can still develop from lower establishment rates achieved with less precise sowing systems.
Sowing to a depth of 1.5cm is recommended.
Good establishment is critical for high yields and helps the crop withstand slug and pigeon attack as well as weed competition.
Ideally, cultivation should be done when soil conditions are dry, as rape does not like compaction.
However, the seedbed should be rolled as the rape seed is small and needs good seed-to-soil contact for rapid germination and successful establishment.
Trials from Teagasc Oak Park show that seeding rates should be 60-80 seeds/m2. These figures can be lowered when growing hybrid WOSR varieties.
Teagasc tillage specialist, Shay Phelan, addresses these issues on the latest Tillage Edge podcast.
“Oilseed rape does not like compacted soils. And, unfortunately, this is an issue in many parts of the country right now,” he explained.
“Compaction prevents root penetration. It also prevents plants from properly anchoring on the ground. Lodging will often follow, as will the poor uptake of nutrients.
“Particularly for growers looking at direct or min-till establishment options, they need to look at ways of relieving these compaction issues before they start drilling.”
Varieties
According to Phelan, there is a niche market for Clearfield WOSR varieties. These allow growers to spray with a herbicide that will take out a range of brassica weeds.
“The downside is that varieties of this type tend to be a little bit on the down side when it comes to the overall yield secured,” he said.
“We could be talking about a drop in the region of 5% to 10%.
“But, that said, if standard WOSR varieties are sown out in fields where there is a lot of competition from brassica weeds, the fall-off in final yield secured could be much more significant than that which would be accepted by sowing a Clearfield variety in the first instance.”
Clubroot is an issue that has raised its head as an issue for winter oilseed rape over the past couple of years ago.
Driving the problem may well be the inclusion of brassica varieties in catch or cover crop mixes.
Phelan advised that a number of clubroot WOSR varieties are now available.
“It’s very much a case of growers chatting to their local seed merchant, where this matter is concerned. But again, the use of clubroot tolerant varieties brings with it a yield penalty of between 5% and 10%,” he said.