Why does your Hosta fortunei have tiny black flies? Diagnose the cause and fix it with our step-by-step guide.
The tiny black flies are likely fungus gnats, whose larvae thrive in the moist, organic-rich soil that Hostas prefer. The adults emerge to lay eggs in the top layer of the substrate, and their larvae can occasionally damage small developing hosta root hairs.
A high concentration of decomposing mulch or compost around the base of your Hosta provides both food and habitat for various small flies. This is less a disease and more an ecological byproduct of nutrient-rich soil management.
While the flies themselves are likely gnats, their presence often indicates overly damp conditions that can lead to Black Scab. This fungal pathogen thrives in high humidity and can cause dark lesions on Hosta leaves.
Your plant might also be experiencing one of these issues:
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