Why Does My Artichoke Have Powdery Mildew?

Powdery mildew on artichoke leaves appears as a white or pale grey powdery coating on the leaf surface — usually on the upper face of the leaves rather than the underside. It is caused by fungal pathogens (primarily Leveillula taurica in artichokes) that thrive in the warm, dry days with cool nights typical of late summer in the UK. Unlike many fungal diseases, powdery mildew does not require free moisture on the leaf surface — it infects in dry conditions when relative humidity is high but the actual leaf surface is dry.

Why late summer artichokes get mildew

By August and September, artichoke leaves are mature and beginning to age — their defences against fungal infection decline as they approach senescence. Warm, dry days followed by cool nights create the humidity fluctuations that favour mildew infection. Dense planting that restricts air movement around the leaves extends periods of high humidity around the foliage. There is usually nothing specifically wrong with plant management when artichoke leaves develop mildew in late summer — it is largely seasonal.

Reducing severity

Watering consistently and sufficiently reduces drought stress, which makes plants less susceptible. Watering at the base rather than overhead reduces the humidity around the foliage. Removing the most heavily mildewed leaves reduces the spore source on the plant. Applying a potassium bicarbonate or sulphur-based fungicide spray every 14 days from the first appearance of mildew suppresses further spread.

End-of-season cleanup

At the end of the season, cut back all stems and remove all leaf material from the site — do not compost heavily mildewed leaves. The mildew fungus overwinters on plant debris and infected plant material, providing the inoculum source for the following season. A thorough autumn cleanup significantly reduces the following year's mildew pressure.

Effect on head quality

Mildew on leaves does not directly affect harvested heads — the heads are not infected. However, severely mildewed plants lose photosynthetic capacity early and may be slightly less productive the following season. Manage mildew primarily to protect the plant's long-term productivity.