Lactuca sativa White Powder - Causes & Fixes

Jump to cause: Powdery Mildew Whiteflies Mineral/Salt Buildup

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Powdery Mildew

This fungal disease, caused by Oidium neovulgaris, is the most common cause of white, flour-like patches on lettuce leaves. It thrives in high humidity and moderate temperatures, often appearing first on older leaves.

Very Common

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How to confirm: Inspect the underside of the leaves for fuzzy white growth that looks like dusted flour.

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1 Apply an organic fungicide to the affected leaves to stop the spread of the fungal spores.

Bonide Captain Jack's Copper Fungicide 32 oz

0.9 L • 1 pcs • Organic

$12

In Stock

2 Prune and remove the most heavily infected older leaves to prevent the fungus from spreading to new growth.

3 Improve air circulation around your lettuce and reduce humidity by spacing plants further apart.

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Whiteflies

Infestations of whitefly larvae or adults can create a white, dusty appearance on the foliage. These insects also excrete honeydew, which can lead to secondary issues like sooty mold.

Common

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How to confirm: Gently shake a leaf over a white piece of paper to see if tiny white insects fly away.

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shopping_cart Recommended Products

1 Apply an organic insecticide to eliminate adult and larval whiteflies and prevent further infestation.

Bonide Captain Jack's Neem Oil 32 oz

0.9 L • 1 pcs • Organic

$10

In Stock

2 Use yellow sticky traps to capture flying adults and monitor the population levels.

Super Ninja Fungus Gnat Traps - 30 Pack

30 pcs

$7

In Stock

3 Wipe the leaves with a damp cloth to remove the white residue and honeydew buildup.

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Mineral/Salt Buildup

Excessive irrigation with hard water or high fertilizer concentrations can leave white, crusty deposits on the leaf surface as water evaporates. This is often seen in hydroponic lettuce or heavy fertigation setups.

Common

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How to confirm: Check if the white spots are crusty and located primarily near the edges of the leaves where evaporation occurs.

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shopping_cart Recommended Products

1 Flush the growing medium or hydroponic reservoir with distilled or demineralized water to leach out accumulated mineral salts.

2 Dilute your nutrient solution and ensure you are using a high-quality fertilizer to prevent future salt concentration spikes.