Why does your Rhododendron decorum have tiny black flies? Diagnose the cause and fix it with our step-by-step guide.
The presence of tiny black flies in the soil of a Rhododendron is most commonly due to fungus gnats, whose larvae feed on organic matter and fungal mycelia in overly moist potting media. High humidity and frequent watering—which Rhododendrons often require—create the perfect breeding ground for these pests.
While not a 'fly' itself, the presence of gnats often signals that the Rhododendron's substrate is too wet, which can trigger Phytophthora root rot. This pathogen thrives in the same anaerobic, waterlogged conditions that support high populations of black flies.
If there is decomposing organic mulch or overripe fallen petals around the base of your Rhododendron decorum, fruit flies may be present. While they do not feed on the plant itself, their presence indicates high moisture levels and decaying matter that can indirectly lead to fungal issues in the soil.
Your plant might also be experiencing one of these issues:
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