Hydrangea macrophylla Glowing Alps White Cottony Spots - Causes & Fixes

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Mealybugs

These small, soft-bodied insects secrete a white, waxy, cottony substance to protect themselves while feeding on the sap of the Hydrangea leaves and stems. Their presence often leads to leaf yellowing and stunted growth in 'Glowing Alps' varieties.

Very Common

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How to confirm: Inspect the crevices of the stems and the undersides of leaves for tiny, moving insects hidden within the white fluff.

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

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

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

Fiskars 5/8" Bypass Pruning Shears

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Cottony Scale

Similar to mealybugs, scale insects produce a white, filamentous covering that resembles cotton. They attach themselves firmly to the plant tissue, sucking nutrients and potentially causing sooty mold growth on the hydrangea foliage.

Common

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How to confirm: Look for stationary, raised bumps under the cottony mass that do not move when poked with a toothpick.

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shopping_cart Recommended Products

1 Treat the plant with an organic insecticide/miticide spray to eliminate the scale insects and their protective white coverings.

Bonide Captain Jack's Neem Oil 32 oz

0.9 L • 1 pcs • Organic

$10

In Stock

2 Physically remove visible scale clusters from stems and leaves using a cotton swab dipped in rubbing alcohol to prevent further nutrient loss.

3 Monitor the plant's environment and ensure good airflow to prevent the secondary growth of sooty mold.

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Powdery Mildew (Early Stage/Fungal)

While typically presenting as a fine dust, certain fungal colonies can appear as thicker, white patches on the surface of hydrangea leaves in high humidity. This is common in 'Glowing Alps' if there is poor air circulation around the dense foliage.

Common

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How to confirm: Check if the white spots can be rubbed off easily with your finger and if they appear more like a coating than a physical mass.

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1 Apply an organic fungicide to the affected leaves to eliminate the fungal colonies and prevent the spread of powdery mildew.