Why does your Allium cepa Tough Ball F1 have tiny black flies? Diagnose the cause and fix it with our step-by-step guide.
The larvae of fungus gnats live in the moist, organic-rich topsoil around onion bulbs, feeding on decaying matter and fine root hairs. The adults emerge to lay eggs, often attracted to the high moisture levels required for Allium bulb development.
While not caused by flies, fungal pathogens like Pythium or Fusarium can cause damping-off; the resulting decaying plant tissue and increased soil moisture attract scavenging flies.
If the onions are in an area with decomposing organic mulch or nearby rotting fruit, these flies may be present in the vicinity of the Allium crop, though they do not feed directly on the onion bulbs.
Your plant might also be experiencing one of these issues:
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