Fungus gnats and growing media

M.R. Nemati
Fungus gnats are considered as one of the most important insect pests of greenhouses and nurseries. A 3-year indoor and outdoor study was performed in Quebec, Canada to increase our knowledge of the biology of fungus gnats, on their favored substrates and conditions for development and reproduction, and on their life cycle in growing media. We were also interested in identifying the best monitoring and controlling techniques for fungus gnats. Several components as well as commercial growing media were exposed to a source of infestation in the greenhouse and the presence and development of fungus gnats in these substrates were monitored over time. Our results indicated that composts, and in particular composted pine bark, are the most attractive substrates for adult fungus gnat females to lay eggs. Based on this work, materials with higher rates of decomposition, which have a high level of microbial activity, are favorable for fungus gnat breeding. We also prepared several exterior experimental piles made from the most common raw materials for manufacturing growing media and monitored them for fungus gnat activity. It was shown that fungus gnats reproduce actively from September to November in Quebec. Our findings show that the population of fungus gnats decreased sharply during winter and increases in spring as soon as the temperature exceeds 7°C. The moisture content of organic substrate plays an important role in selection of laying site and the development of fungus gnat larva. Our investigation with infested raw materials showed that the most of fungus gnat population can be eliminated during the manufacturing process principally due to mechanical processes such as sieving and mixing. Several additional strategies to control fungus gnat population were identified in this study.
Nemati, M.R. (2021). Fungus gnats and growing media. Acta Hortic. 1305, 125-130
DOI: 10.17660/ActaHortic.2021.1305.18
life cycle, infestation, monitoring, controlling techniques, biological and chemical controls, pine bark, compost

Acta Horticulturae