11 August 1995

Surveys reveal split opinion on rape carryover

HIGH erucic acid rape volunteers may or may not pose a risk to following crops of food grade rapeseed, depending upon who you listen to.

An ADAS survey of most HEAR producers suggests cultivations need improving to prevent carryover. But a survey of fields in East Anglia by independent consultant Mara Ramans suggests volunteers are few and unlikely to harm food crops.

The ADAS survey questioned 95% of HEAR producers, 45% of whom said they would sow a food grade crop in the rotation after a HEAR crop. Many were taking action to minimise volunteers.

Lengthening the rotation was not popular, cultivations being preferred by most. But many failed to get a good chit between harvest and cultivations, risking the burial of viable seed, which would create volunteer problems later.

Leaving land uncultivated after harvest is the best strategy for reducing volunteers, the ADAS workers suggest. Yet more than one in four growers plough within three days of harvest. Fewer than a quarter of growers use shallow cultivations to stimulate emergence and destroy seedlings before ploughing.

A massive 63% plough with no prior cultivation. There is a clear need for better advice to growers, concludes the ADAS team.

But Ms Ramans survey of 38 fields in East Anglia showed fewer than one HEAR volunteer per square metre emerging after five years. That is "unlikely" to cause erucic acid levels to rise above 2% if a double-low crop is grown. At least 8% volunteers is required to produce a 2% rise in erucic acid levels, she adds. &#42