Oilseed rape establishment

A simple blueprint for establishing oilseed rape is impossible. The crucial thing to remember is that the most important day in the crop’s life is the day of drilling, so be prepared to make decisions based on the conditions.

Target population

Before winter sets in you should have large, deep-rooted and robust plants achieving good ground cover to capture light. You should also have good soil structure, allowing effective drainage. If you achieve these factors, your crop will be:

More rapidly established
More slug tolerant
More phoma tolerant
More difficult for pigeons to land in
More competitive against weeds
More able to tolerate difficult winter conditions

In good growing conditions the target spring population is 25-40 plants/sq m with larger biomass types at the lower end of the range. These target plant populations are the same across row widths ranging from 12cm to 48cm. The sowing rate to achieve the target plant numbers will typically be 40-80 seeds/sq m, the final decision being made on the day of drilling based on seed-bed conditions. Always calculate the rate by seeds/sq m (not kg/ha) as thousand seed weights vary enormously.

Drilling date and variety choice

Target drilling date is mid-August through to early September, although in the north of England and Scotland aim for August drilling. The aim is to have robust plants going into winter with big roots, and earlier drilling is much more likely to achieve this. However, many crops are established after winter wheat, which often pushes the drilling date later.

Varieties with fast early development and good early vigour tend to improve the chances of good establishment when crops are sown late or into poor seed-beds. There are both hybrid and conventional varieties with these traits. Given the rapid turnover of OSR varieties, it is best to check with plant breeders and seed suppliers which varieties have these traits.

Cultivation and drilling

Winter rape is lazy rooting so make sure subsoil structure is good to allow the roots to grow down and to permit drainage. Assess soil structure by digging holes and deal with compaction if required.
The very small seed requires a tilth fine enough to achieve good seed/soil contact. Drilling depth is 15-25mm. Rolling is essential.

Bearing these points in mind, the crop can be established by a range of methods. Attention to detail on how the machinery is set up and used for the field conditions on the day is critical. Under dry conditions moisture conservation is a prime consideration, particularly on heavy soils.

Soil type and seed-bed have a big influence on establishment. Heavy soils present more challenges where a finer tilth is required for the same soil moisture content to allow seed germination. Cloddy seed-beds will dry out faster, due to more air movement, and will increase slug pressure significantly.

Previous herbicide use may determine cultivation needs. For example, if iodosulfuron and mesosulfuron-containing products such as Atlantis, Pacifica or Othello (Othello also contains diflufenican) have been applied after 1 February, land must be ploughed (or heavy cultivated to at least 15cm) before drilling rape. However, there are no cultivation restrictions if Unite (flupyrsulfuron + pyroxsulam) and Broadway Star (florasulam + pyroxsulam) have been applied in the previous crop.

Seed-bed nutrition

Oilseed rape can put on a lot of growth pre-winter and has a high nutritional demand during autumn – much greater than cereals. Where soil indices of P, K or Mg are low, apply fertiliser to the seed-bed and ensure it is mixed in to maximise nutrient availability to the plant as it establishes. Seed-bed nitrogen may be needed to help get the crop away, particularly when drilling is not early or where straw has been incorporated. Apply up to 30kg/ha of N either in the seed-bed or by very early establishment.

There are various blends of liquid and granular fertilisers that can meet these nutritional demands. Some of the granular fertilisers or blends can be mixed with the seed to bulk up low seed rates, in addition to supplying nutrients.

Pest management

In the absence of neonicotinoid seed treatments the focus should be on taking all possible steps to achieve rapid establishment to help combat pests and in particular cabbage stem flea beetle and slugs.

Cabbage stem flea beetle (CSFB)

Although not the most scientifically precise method a quick look in the trailers of harvested OSR seed will give an indication of the number of CSFB available to invade crops. If beetles are easily seen hopping around in the trailers then there is clearly a risk to an emerging crop.

Yellow water traps in proposed OSR fields will catch CSFB. Traps should also contain a drop of washing-up liquid so that any insects caught sink and drown. They should be examined regularly as they will catch large numbers of insects, which can make it difficult to pick out CSFB.

Yellow sticky traps can also be used to monitor beetle numbers. Regular inspection is again recommended, as large numbers of different insects will be caught. The presence of beetles indicates a need to monitor crop emergence.

Once the crop has emerged, monitor regularly for shot-holing due to CSFB adults. Remember that the presence of holing does not necessarily justify insecticide treatment as a rapidly establishing crop can grow away from pest damage. Pyrethroid sprays are the only available option for adult CSFB control. Resistance has been detected in Germany so there is a risk that this could spread to the UK. Pyrethroids should only be used if absolutely necessary. Treat if 25% of leaf area has been eaten at the 1-2 leaf stage and 50% of leaf area at the 3-4-leaf stage.

Slugs

Slugs are a regular threat to establishment if wet weather favours their activity. As with CSFB rapid establishment is key as plants can tolerate some leaf grazing. Take special care to apply pellets, when required, safely to minimise the risk of them entering watercourses. Once beyond the four-leaf stage plants are no longer considered susceptible to losing yield from slug attack.

Weed management

There are limited options for cultural weed control in oilseed rape. Delaying drilling by a substantial amount is not feasible and will often comprise the establishment of a competitive crop, which in turn reduces the level of weed suppression.

It is important to know what weeds are likely to emerge as weed control in oilseed rape is predominantly based on autumn application with many applications being made pre- or very early post-emergence. Metazachlor forms the basis of most oilseed rape herbicide programmes and it can be used in combination with, dimethenamid-p (cranes’s bill) clomazone and quinmerac (cleavers). Label rates should be applied to achieve effective control. Where seed is not covered by a minimum of 15mm soil (check product label) or if heavy rainfall is expected, early post–emergence applications will be safer.

Cereal volunteers and grassweeds can compete with the emerging crop and should be removed with a graminicide at growth stage 12 of the weed – when 2 leaves have emerged.

Blackgrass control in oilseed rape is difficult; most populations have a moderate to high level of resistance to some graminicides used in oilseed rape. Some control can come through the use of metazachlor applied pre-emergence. No resistance to the post-emergence herbicide active ingredients propyzamide (in Kerb Flo 500) and carbetamide (in Crawler) has been recorded, with applications of these herbicides usually beginning when the crop has 3-4 leaves and soil temperature falls below 8-10°C (early November). Propyzamide forms a layer in the top 5cm of soil and any weeds germinating in this layer can be controlled by the herbicide. These herbicides are best used in combination with shallow cultivations rather than ploughing to keep weed seeds in this layer.

Astrokerb is an alternative product to Kerb Flo 500 and contains propyzamide formulated with the additional active ingredient aminopyralid and gives additional control of broad-leaved weeds such as poppies, mayweed and sow thistle.

When using actives such as propyzamide and carbetamide, special care should be taken to avoid the materials entering watercourses, see the information published by the voluntary initiative concerning these products.

Which establishment system?

Autocast

Pros: Cheap and quick; low soil moisture loss, can reduce weed pressure, potentially better control of blackgrass by herbicides such as propyzamide due to shallow rooting.

Cons: Unreliable establishment; poor rooting; unlikely to produce high yields; high slug pellet requirement. Cannot use treated seed or pre-emergence herbicides as not all seed is covered with soil.

Sub-casting system (Sub-soiler broadcast) and direct drilling

Pros: Sub-casting provides good subsoil management with excellent rooting. Both sub-casting and direct drilling offer a one pass and relatively cheap operation; low soil moisture loss, less weed pressure due to reduced soil disturbance.

Direct drilling with Horch, Dale and Vaderstad systems, among others, can offer high work-rates and do not disturb the soil surface as much as sub-casting. This can improve the performance of post-emergence herbicides such as propyzamide against blackgrass, as the weed germinates from a shallower depth and increases absorption of the active ingredient by the plants.

Cons: On heavy soils and in dry conditions, very little tilth may be produced resulting in limited seed/soil contact and seed dropping down cracks; pressure from slugs can be higher as they move up the loosened soil; may not be as effective in wet soil; relatively slow operation but single pass. Sub-casting can leave seed exposed and limit pre-emergence herbicide options (in some cases growers will power harrow over the top of the sub-cast rape so they can use pre-emergence herbicides).

Cultivator broadcaster

Pros: Potentially rapid single-pass operation; some can work deeper; cheap, good moisture conservation.

Cons: Seed depth can limit herbicide options; may not address subsoil condition.

Plough and drill

Pros: Reliable under a wide range of conditions and soil types; weed and cereal volunteer control easier to manage due to lower populations; nitrogen mineralisation can speed up crop establishment.

Cons: Slow and expensive; requires rapid reconsolidation to conserve moisture in dry conditions; can be difficult to get fine enough seed-bed on heavy soils; potentially poorer control of blackgrass due to variable emergence depths.

This Academy was written by Dr Pete Berry with contributions from Dr Sarah Cook, research consultant at Adas, and Dr Steve Ellis, entomologist, Adas.

Source: http://academy.fwi.co.uk/Courses/Arable/Oilseed-rape/Oilseed-rape-establishment