In 2007 the New Zealand Society of Plant Biologists renamed their annual award after Slack. The award is made to society members to recognise an outstanding contribution to the study of plant biology. It was renamed in recognition of his outstanding contribution as a plant biologist and biochemist in New Zealand, his role in the discovery of C4 photosynthesis (also known as the Hatch Slack Pathway), and his contribution as an early member of the New Zealand Society of Plant Biologists.