Hydrangea macrophylla Glowing Alps Tiny Black Flies - Causes & Fixes

search Possible Causes

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Fungus Gnats

The larvae of these flies live in organic-rich, moist soil and feed on decaying matter or fine root hairs. In Hydrangeas, high moisture levels required for their large leaves often create the perfect breeding ground for these pests.

Very Common

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

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1 Deploy yellow sticky traps to capture adult flies and disrupt the breeding cycle.

Super Ninja Fungus Gnat Traps - 30 Pack

30 pcs

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2 Allow the top inch of soil to dry out completely between waterings to kill larvae in the organic matter.

GROWIT Analog Soil Moisture Meter

Water Meters

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3 Apply a biological control or organic insecticide to target the larvae and prevent further infestation.

Bonide Captain Jack's Neem Oil 32 oz

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Overwatering and Soil Compaction

While Hydrangeas love moisture, stagnant water in heavy soil lacks oxygen, triggering the emergence of fungus gnats. This condition can also lead to root rot, which further weakens the 'Glowing Alps' cultivar.

Very Common

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How to confirm: Insert your finger two inches into the soil; if it feels muddy or holds water long after watering, the substrate is too wet.

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shopping_cart Recommended Products

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

GROWIT Soil Moisture Meter SMM-V3

Water Meters

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2 Repot the hydrangea in a well-aerated, high-porosity medium and mix in perlite to improve drainage and prevent soil compaction.

3 Apply yellow sticky traps to capture and remove the adult flying insects from your plant environment.

Super Ninja Fungus Gnat Traps - 30 Pack

30 pcs

In Stock

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Excessive Organic Matter in Potting Mix

A high concentration of decomposing peat moss or compost provides an abundant food source for fly larvae. This is particularly common in decorative indoor potting mixes used for ornamental Hydrangeas.

Common

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How to confirm: Check if the soil surface has a thick layer of decomposing mulch or uncomposted organic material where flies are congregating.

build How to fix it

shopping_cart Recommended Products

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

Bonide Captain Jack's Neem Oil 32 oz

0.9 L • 1 pcs • Organic

$10

In Stock

2 Use yellow sticky traps to capture adult fungus gnats and prevent further breeding in the soil.

Super Ninja Fungus Gnat Traps - 30 Pack