Why does your Begonia grandis have tiny black flies? Diagnose the cause and fix it with our step-by-step guide.
These small black flies are the larvae of fungus gnats, which thrive in the moist, organic-rich soil typically used for Begonia grandis. The adults emerge to lay eggs in the top layer of soil, while the larvae feed on organic matter and can damage delicate Begonia root hairs.
Begonia grandis prefers consistent moisture but is highly susceptible to root rot if the soil remains saturated. Excessively wet substrate provides the perfect breeding ground for fungus gnat larvae and can weaken the plant's structural integrity.
The presence of decaying leaves or uncomposted bark in the Begonia's potting mix provides a food source for fly larvae. As organic material breaks down, it creates an environment that attracts moisture-seeking insects.
Your plant might also be experiencing one of these issues:
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