A quarter of Australia's vegetable growers are forced to abandon valuable produce which is left to rot because they can't find enough workers to pick and pack it, a new report has found.

The study's project leader, Associate Professor Joanna Howe, from the University of Adelaide Law School, said the challenge in finding labour had become unsustainable and the amount of waste was a significant loss to the Australian economy.

Aldi's new store format increases space dedicated to fresh food from 15 to 25 per cent. Credit:Brendon Thorne

"We are seen as the food bowl of Asia, but if we don't have the workers to get the produce out from the farms and into the supermarkets and out for export, it is a real concern about the sustainability of that industry," she said.

"It means that growers are finding it hard to expand because they are not sure they have enough workers to meet that expansion.