Pelargonium zonale Tiny Black Flies - Causes & Fixes

Jump to cause: Fungus Gnats Overwatering and Soil Moisture Imbalance Decaying Organic Matter

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Fungus Gnats

The tiny black flies are likely the adult stage of fungus gnats, which breed in the moist top layer of soil. Their larvae feed on organic matter and can damage the fine root hairs of your Pelargonium, leading to stunted growth.

Very Common

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How to confirm: Perform a 'sticky trap test' by placing a yellow adhesive trap near the soil surface to see if small flies are captured.

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1 Reduce watering frequency and allow the top inch of soil to dry out completely to disrupt the fungus gnat breeding cycle in the moist soil.

GROWIT Soil Moisture Meter SMM-V3

Water Meters

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2 Deploy yellow sticky traps near the plant surface to capture adult flies and prevent further egg-laying.

Super Ninja Fungus Gnat Traps - 30 Pack

30 pcs

$7

In Stock

3 Repot the geranium in a well-draining medium and consider adding perlite to improve aeration and prevent soil compaction.

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Overwatering and Soil Moisture Imbalance

Pelargoniums prefer their soil to dry out significantly between waterings. Constant moisture creates a perfect breeding ground for fungus gnat larvae and promotes fungal pathogens in the rhizosphere.

Very Common

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How to confirm: Insert your finger two inches into the soil; if it feels damp while flies are present, you are watering too frequently.

build How to fix it

shopping_cart Recommended Products

1 Reduce watering frequency to allow the top inch of soil to dry out completely, breaking the fungus gnat breeding cycle.

GROWIT Soil Moisture Meter SMM-V3

Water Meters

—

2 Apply yellow sticky traps near the soil surface to capture adult flies and prevent further reproduction.

Super Ninja Fungus Gnat Traps - 30 Pack

30 pcs

$7

In Stock

3 Repot the plant in a well-draining medium amended with perlite to improve aeration and prevent future moisture imbalance.

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Decaying Organic Matter

Old, decomposing potting media or fallen dead leaves at the base of the Geranium provide essential nutrients for fly larvae. This organic decay attracts scavengers and moisture-loving insects.

Common

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How to confirm: Inspect the soil surface for any rotting plant debris or old mulch that needs to be removed.

build How to fix it

shopping_cart Recommended Products

1 Remove all fallen dead leaves and debris from the base of the plant and the top of the soil to eliminate breeding sites.

2 Apply a biological insecticide to target the larvae and adult flies in the soil.