Hydrangea macrophylla Magical Bluebells White Cottony Spots - Causes & Fixes

Jump to cause: Mealybugs Powdery Mildew Cottony Root Rot (Phytophthora)

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Mealybugs

These small insects secrete a white, waxy substance that looks like cotton to protect themselves. They cluster in the leaf axils and tender new growth of Hydrangeas, sucking sap and weakening the plant.

Very Common

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How to confirm: Use a magnifying glass to look for tiny, slow-moving insects hidden at the base of leaves or stems.

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1 Isolate the plant immediately to prevent the mealybugs from spreading to other greenery and spray the affected areas with an organic insecticide.

Bonide Captain Jack's Neem Oil 32 oz

0.9 L • 1 pcs • Organic

$10

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2 Use a cotton swab dipped in isopropyl alcohol to manually remove visible white waxy clusters from leaf axils and stems.

3 Prune away any heavily infested or dead stems using clean, sharp shears to reduce the pest population.

Fiskars 5/8" Bypass Pruning Shears

Cutting Tools

$13

In Stock

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Powdery Mildew

This fungal pathogen thrives in high humidity and poor air circulation around the dense foliage of Hydrangeas. It manifests as a white, dusty coating on the surface of leaves that can eventually lead to leaf drop.

Very Common

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How to confirm: Check if the white spots can be rubbed off easily with your finger like flour or dust.

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1 Apply an organic fungicide to eliminate the existing fungal spores and prevent the spread of the mildew.

Bonide Captain Jack's Copper Fungicide 32 oz

0.9 L • 1 pcs • Organic

$12

In Stock

2 Improve air circulation around the foliage by pruning dense areas and ensure the plant is not in a high-humidity pocket.

3 Avoid overhead watering to keep the leaves dry, as moisture on the leaf surface encourages fungal growth.

Chapin 48000 0.5G Watering Can

2.3 L • Recycled Plastic

$12

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Cottony Root Rot (Phytophthora)

While primarily a root issue, advanced decay in Hydrangeas can sometimes manifest as white, fungal mycelium appearing on the soil surface or base of the stem. This is often accompanied by wilting despite moist soil.

Common

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How to confirm: Gently lift the edge of the soil to check if the base of the stems feel soft, mushy, or dark.

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shopping_cart Recommended Products

1 Inspect the base of the stems and soil surface for any soft, mushy, or decaying plant tissue and carefully prune away any heavily infected areas using sterilized shears.

Fiskars 5/8" Bypass Pruning Shears

Cutting Tools

$13

In Stock

2 Apply a fungicide to the affected area to control the spread of the fungal mycelium and prevent further decay of the root system.

Bonide Captain Jack's Copper Fungicide 32 oz

0.9 L • 1 pcs • Organic

$12

In Stock

3 Improve soil aeration and drainage by mixing in horticultural perlite to prevent the waterlogged conditions that favor Phytophthora growth.