How volunteers affect erucic acid risks in oilseed rape
Higher than expected levels of erucic acid have been found in seed grown from double-low oilseed rape (OSR) varieties. Management of volunteers during the pre-planting period is one of the key steps to keep levels below legal/contractual requirements.
How does volunteer OSR influence erucic acid risks?
OSR volunteers are associated with elevated levels of erucic acid. In fact, they may be the primary source of contamination in double-low OSR crops – either directly, through their seed; or indirectly, through cross-pollination.
To ensure OSR crops maintain low levels of erucic acid, it is important to understand the history of any field used in its production. Routes of contamination mean that, ideally, 15 years’ worth of (cropping/weed) data is required.
Short rotations (for example, OSR grown more than once every five years) not only reduce OSR yield, but are associated with a build-up of OSR volunteers – potentially including volunteers with elevated erucic acid.
Most freshly shed OSR seed has low dormancy and will germinate if adequate moisture is available. However, under dry conditions, OSR seed develops dormancy in the first month after being shed, especially under cold and dark conditions. Once buried, approximately 5% of seeds will remain viable after three years and some may even be viable for up to 15 years.
Ploughing brings old seed to the surface. As seeds can remain viable for many years and because a single volunteer OSR plant can produce around 2,000 to 10,000 seeds, it is clear to see why their management is essential.
Any cultivation should, therefore, be delayed (ideally, by at least four weeks) to allow volunteers and weeds to emerge and be sprayed off with a non-selective herbicide.
A predictive test is being developed by NIAB to analyse leaf samples for the presence of the genes responsible for the production of erucic acid.