And the ACT Supreme Court heard the women should be given a jail sentence for the publicity stunt in July last year.

NSW women Jessa Latona, 35, and Heather McCabe, 48, pleaded guilty to one charge of damaging or destroying Commonwealth property.

Latona and McCabe, both volunteers with the conservation group Greenpeace, scaled fences to break into a CSIRO farm at Ginninderra on July 14 last year.

They filmed themselves vandalising a trial crop of wheat which had been genetically engineered to increase its nutritional value.

Greenpeace used the incident to garner publicity over the issue of genetically modified crops, releasing video of the women destroying the wheat with whipper snippers.

Yesterday Justice Hilary Penfold said the stunt ''wasn't particularly effective'' and the women had not appreciated how much the offences would cost Greenpeace.

The court heard the conservation group had paid the $280,000 reparation for the women but Justice Penfold questioned whether the payment was a sign that the pair were taking responsibility for their actions because they had suffered no financial loss in making the payment.

Commonwealth prosecutor Duncan Berents said the vandalism had a wide impact on the CSIRO, delaying the wheat trial by 12 months.

Mr Berents said Latona and McCabe had limited insight into their actions and had expressed little remorse.

The court heard imprisonment was the only appropriate starting point for a sentence.

But defence barrister Matt Johnston said his clients had been concerned about the risks of genetically modified products and the lack of transparency surrounding the CSIRO trial.

He said Latona and McCabe had taken responsibility for the offence, handing themselves in to police, co-operating fully with the investigation and pleading guilty.

Justice Penfold postponed handing down her sentence until at least October to allow for Latona, who is heavily pregnant, to give birth. But she indicated she would give the women fully suspended sentences.