Harvest and erucic acid risk in oilseed rape

Higher than expected levels of erucic acid have been found in seed grown from double-low oilseed rape (OSR) varieties. There are several steps you can take during the harvest period to help keep levels below legal/contractual requirements.

How you approach harvest and manage the post-harvest grain influence erucic acid risks.

Firstly, it is important to reduce the amount of seed shed in the field, because this increases volunteer OSR numbers, which may be associated with elevated levels of erucic acid. This makes it even more important to reduce pod shatter – for example, by taking steps to promote crop uniformity and harvesting the crop at the optimum stage of maturity. Use records of any excessive pod shatter to guide rotational planning.

Secondly, there is a risk that seed from double-low varieties may become mixed with varieties associated with higher levels of erucic acid (e.g. HEAR varieties). As a result, it is essential to segregate double-low crops from other crops (and farm-saved seed and weed-burdened crops) at all times and to thoroughly clean machinery, trailers and stores.

Thirdly, it is important to retain a representative sample of each variety by field or – ideally – by trailer. Additionally, a representative sample of each load of seed leaving the farm should also be kept. Write any erucic acid results on the appropriate record. Retaining representative samples provides an opportunity for retesting (in case of any dispute) and to identify specific fields with specific problems.

It is essential to read and understand any contract before it is signed. It is also important to keep records of all contract.

Traditional methods of detecting erucic acid involve extracting oil and using gas chromatography (GC) techniques. Cheaper, more modern, near-infrared (NIR) spectrophotometer (NIRS) scanning techniques are increasingly used, including at intake on whole rapeseed.

Recent AHDB-funded research found that NIRS can give erucic acid values that correlate well with those obtained by GC analysis of the wide range of levels (0–40%) tested. However, NIRS accuracy was found to be significantly reduced at the narrower and critical 0–5% range, with ‘considerable inaccuracy’ at the 0–2% range. GC remains the most accurate method, especially for measuring lower levels (below 2%).

Any elevated levels of erucic acid detected could point to a source of contamination, which will require investigation. If seed is rejected on the basis of a high NIRS test reading, it is recommended to retest using GC.