Pre-harvest choices for successful oilseed crops

6 July 2001

Pre-harvest choices for successful oilseed crops

To maximise harvested

oilseed rape yield, growers

need to plan pre-harvest

treatments with care. Our

latest Oilseeed Rape Adviser

article, sponsored by PBIC

Seeds, summarises the key

options for this harvest

CONSIDER the effects of site, weather, weeds, crop evenness and maturity before selecting your harvesting technique for oilseed rape this year.

Sue Ogilvy, of ADAS High Mowthorpe, says in the past harvesting method has tended to be regional, with crops being grown in the north on exposed sites being more suited to swathing than those on fertile sites in the south.

"With a very dense crop, it is best to leave it to ripen on its own. But swathing has a place where the risk of pod shatter and seed loss is high."

Desiccation comes into force when a crop needs evening up. "There was a great deal of patchiness at the start of the growing season and many crops are quite uneven in their development," she says. "It can also help with the removal of weeds because many growers failed to get good control this year."

Crops which are shorter and more open than usual are candidates for direct combining because ripening will be more even, she believes. Equally, thin crops can be combined direct without the need for swathing.

"The decision on whether to spray, swath or direct cut may have to be made on a crop-by-crop basis this year. Some crops established well last autumn, but others struggled to get going."

Swathing

A good method for exposed sites and where harvest can get delayed, swathing is effective for upright or leaning crops and is the best way of preserving yield. It needs a sufficient stubble length of 20-30cm to raise the crop off the ground.

"Very short crops may lose some lower pods with swathing, so if these crops are open they are best direct combined," says Dr Ogilvy. "Lodged crops are also difficult to swath because the pod layer varies in thickness and height off the ground."

Where swathing is preferred, cutting should start six weeks after the end of flowering. "Look at the main raceme and if the seeds on the top third are just beginning to turn brown, then the time is right."

Cutting the swath to the right height will maximise the support provided by lower branches and allow adequate airflow for even drying.

Desiccation

Desiccation is likely to have more of a role for the removal of weeds this year than it will for making harvest easier. Shorter crops should make late spraying operations easier.

ADAS advises that late germinating blackgrass in the base of crops will be controlled if canopy penetration is sufficient, although uncontrolled autumn germinated plants will have shed some seed before desiccation is due.

Choice of desiccant will depend on the required speed of action and the weeds present. The correct timing for treatment is:

lTop third of raceme – more than 50% green seed.

lMid-third of raceme – 90% reddish brown/black brown seeds.

lBottom third of raceme – all seeds dark brown to black.

For the slowest acting products, spraying should be done when more than two-thirds of the seeds on the middle third of the raceme are green/brown. These desiccants are preferred where long-term control of couch and other perennials is required.

Desiccants should be applied as a medium sized droplet in a large volume of water. The use of wetters can help to improve the effectiveness of some desiccants. Hybrid varieties, in particular, will benefit from the use of a desiccant, as they produce a deep canopy structure with a wider range of pod maturities.

Direct combining

Where a desiccant has been used, direct combining can normally start 7-14 days after spraying with the aim of harvesting at 12-15% moisture.

"But if harvest gets delayed, there is a risk that seed will be shed," says Dr Ogilvy. "Especially on exposed sites."

Combining of mature crops should be done when most of the seeds are black and hard. Use of a vertical knife will reduce pod shatter and ease the progress of the combine through the crop.

"Inspect crops for seed ripening and select the harvesting technique which best suits the crops maturity and evenness," advises Dr Ogilvy. &#42

Making the most of oilseed rape as a break crop is a key goal for UK arable farmers. That is why plant breeder PBIC Seeds is sponsoring this series of articles in farmers weekly. Over the year we have examined key issues involved with the crop, keeping you up to date with the latest advice to help ensure oilseed rape is a profitable part of your crop rotation.