Candidates were "whittled down" by trialling them first on pot-grown weeds, with the most promising then applied to field-scale trials, in which they are compared with the standard conventional herbicide glyphosate.
"Nothing works quite as well as glyphosate," he said. "Generally they work best at the seedling stage and could be used in succession, although that makes them more difficult to use."
He added: "They are products that are just starting to be commercialised elsewhere and there are a couple that are potentially more interesting that we know about from the literature.
"Some could be used in organic growing, though if we keep losing conventional herbicides then they may also serve as replacements. There are already question marks against glyphosate in some countries." Atwood is also looking at biological herbicides on fruit, he added.