fungus gnat

Symptoms

Tiny (3mm) black flies running on soil surface + hovering around plants, white translucent larvae visible in top 2-3cm of wet potting mix, young plants stunted with poor growth, mature plants tolerate moderate populations but become vulnerable to root rot.

Easily confused with

• Pythium root rot

  How to tell them apart: Bradysia coprophila (fungus gnat) shows tiny dark adult gnats running or weakly flying over the soil surface, and slender 5-6 mm larvae with a shiny black head and translucent white body wriggling in the top centimetre of wet potting mix; you may see a faint slime-like sheen or fungal bloom on the surface. Pythium aphanidermatum (root rot) produces NO insects at all: instead the lower stem and roots turn soft, brown to black and mushy, and the fine root tips slough off so the outer root sheath slips away leaving a bare thread. With Pythium the Dracaena wilts even though the soil is wet and lower leaves yellow from the base up, while gnat-damaged plants decline more slowly and the visible giveaway is the flying adults and surface larvae, not rotten roots.