Calathea concinna Tiny Black Flies - Causes & Fixes

Jump to cause: Fungus Gnats (Sciaridae) Overwatering and Soil Anaerobia High Organic Matter in Substrate

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Fungus Gnats (Sciaridae)

The larvae of these flies live in the top layers of the soil and feed on organic matter or decaying roots. For Calathea concinna, which prefers high humidity, the moist environment required by the plant is the perfect breeding ground for these pests.

Very Common

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How to confirm: Set a yellow sticky trap near the plant to see if small black flies are captured.

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1 Deploy yellow sticky traps to capture the adult flying gnats and break the breeding cycle.

Super Ninja Fungus Gnat Traps - 30 Pack

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2 Reduce watering frequency and allow the top inch of soil to dry out to make the environment less hospitable for larvae.

GROWIT Soil Moisture Meter - Blue

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3 Top-dress the soil with a layer of sand or fine perlite to create a physical barrier that prevents adults from laying eggs in the organic matter.

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Overwatering and Soil Anaerobia

Excessive moisture in the Calathea's substrate creates a breeding ground for fungus gnats and can lead to root rot. When the soil stays saturated, it attracts flies looking for damp organic material to lay eggs.

Very Common

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How to confirm: Stick your finger two inches into the soil to check if it is staying wet for too long between waterings.

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1 Reduce watering frequency and allow the top inch of soil to dry out completely before watering again to disrupt the fungus gnat life cycle.

GROWIT Soil Moisture Meter SMM-V3

Water Meters

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2 Repot the plant in a well-draining, fresh potting mix enriched with perlite to improve aeration and prevent soil anaerobic conditions.

3 Apply yellow sticky traps near the soil surface to capture adult flies and reduce the population.

Super Ninja Fungus Gnat Traps - 30 Pack

30 pcs

$7

In Stock

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High Organic Matter in Substrate

If the potting mix contains a high amount of decomposing peat moss or compost, it provides an abundant food source for fly larvae. Calatheas often require rich soil, but too much decomposing material can inadvertently attract pests.

Common

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How to confirm: Examine the surface of the soil for small, brownish-white larvae moving near the base of the plant stems.

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1 Apply a biological insecticide to eliminate the adult flies and larvae by targeting the pest life cycle.