This study investigated the potential link between peat-free growing media and the emergence of sciarid flies (fungus gnats) as pests in Scotland. As the use of peat in horticulture declines due to environmental concerns, alternative growing media have been adopted, but their potential impacts on plant health remain unclear. Through stakeholder interviews and literature reviews, the study explored the prevalence and impact of sciarid flies in glasshouse environments.

Findings suggest a lack of scientific research on fungus gnats in Scotland, with most studies focusing on mushroom farms. While 92% of stakeholders believed that fungus gnats originate from purchased growing media, this remains anecdotal. There is no conclusive evidence that peat-free composts are more susceptible to infestations than peat-based mixes.

The project found reports that fungus gnats can act as primary pests, with larvae attacking plant roots and adults spreading pathogens. Effective management strategies include maintaining clean glasshouses, using sticky traps, and controlling growing media moisture levels. Biological controls, such as nematodes and rove beetles, can help manage issues but are often expensive at scale.

The study recommends further research to identify sciarid fly species in Scotland, assess growing media components that attract them, and determine best horticultural practices for controlling infestations, thereby enhancing consumer confidence in peat-free alternatives.

Image courtesy of Robert Webster, xpda.com, CC-BY-SA-4.0