Why Is There White Powder All Over My Pea Plants?

A white or grey powdery coating appearing on pea leaves, stems, and eventually pods — typically from July onward in UK growing conditions — is pea powdery mildew, caused by Erysiphe pisi. This is one of the most common pea diseases and is considered almost inevitable on late-season pea crops in warm, dry years. Unlike most fungal diseases, powdery mildew does not need wet weather to spread — it thrives in warm, dry conditions with moderate air humidity, making July and August the peak months for infection.

Why it appears late in the season

Powdery mildew spores are always present in the garden air but only infect pea plants that are under stress — most commonly heat and water stress in the latter part of summer when temperatures rise and soils dry. The fungus grows entirely on the leaf surface (extracting water and nutrients from surface cells) without needing free water for spore germination, which is why it spreads rapidly in dry, warm conditions that other pathogens cannot exploit. Autumn-sown overwintering peas are largely unaffected because they develop in cool, moist conditions.

Are mildewed pods edible?

Yes — pods with powdery mildew on their outer surface are safe to eat, though the mildew itself is unpalatable. Wash pods thoroughly and open them — the peas inside are unaffected by the external mildew unless the infection has penetrated very deeply, which is unusual. Harvest all pods promptly once mildew is visible because the peas inside deteriorate quickly once the plant is in decline. Very heavily mildewed plants should be removed and composted (powdery mildew composts without persisting as a problem).

Reducing mildew in future seasons

Consistent watering reduces drought stress that makes plants susceptible. Improving airflow between plants (sow at appropriate spacing, avoid too-thick plantings) slows disease spread. Choose mildew-resistant varieties — many modern pea varieties have been bred with improved resistance to powdery mildew (check seed catalogue descriptions). Most importantly, make an early to mid-May sowing rather than a late one — early-sown peas complete their cropping season before the hot July and August conditions that trigger mildew.