Begonia rex-cultorum White Powder - Causes & Fixes

Jump to cause: Powdery Mildew Mealybugs Mineral Deposits (Hard Water)

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Powdery Mildew

A common fungal disease caused by high humidity and poor air circulation, appearing as a white, flour-like coating on the Rex Begonia's leaves. This fungus thrives when moisture sits on the foliage of these tropical plants.

Very Common

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How to confirm: Inspect if the white patches can be rubbed off with your finger, leaving a bruised or discolored spot underneath.

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1 Apply an organic fungicide to eliminate the existing fungal spores and prevent further spread across the foliage.

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2 Improve air circulation around the plant and avoid wetting the leaves during watering to prevent new fungal growth.

3 Prune and discard any heavily infected leaves to reduce the fungal load on the plant.

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Mealybugs

Small, soft-bodied insects that secrete a white, waxy, cottony substance to protect themselves. In Rex Begonias, they often cluster in the crevices between leaf petioles and the stem.

Common

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How to confirm: Use a magnifying glass to look for tiny, slow-moving insects nestled in the leaf axils or under the foliage.

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1 Isolate the plant immediately to prevent the mealybugs from spreading to your other houseplants.

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

3 Apply an organic insecticide spray to the entire plant to eliminate any remaining insects and larvae.

Bonide Captain Jack's Neem Oil 32 oz

0.9 L • 1 pcs • Organic

$10

In Stock

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Mineral Deposits (Hard Water)

Accumulated calcium or magnesium from tap water can dry on the leaf surface as a white, crusty residue. Unlike fungus, this is inorganic and does not spread across the leaf tissue.

Common

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How to confirm: Check if the white spots are hard/crusty and located primarily near the edges or tips of the leaves where water evaporates.

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1 Gently wipe the leaves with a soft, damp cloth using distilled or filtered water to remove the mineral crust without damaging the delicate foliage.

2 Switch to using rainwater or distilled water for future watering to prevent new calcium and magnesium deposits from accumulating on the leaves.

3 Monitor soil moisture levels to ensure you are not overwatering, which can exacerbate mineral buildup in the substrate.