Pea: white powdery coating on leaves

What it is likely to be on pea

1. Powdery mildew

   Candidate 1very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Powdery mildew

   Checked 2026-08-13

   A white, floury coating on the upper leaf surface, most familiar on courgettes and cucumbers late in the season. Unlike most fungal diseases it does not need the leaves to be wet — it needs the roots to be dry and the air to be humid, which is why it arrives in a warm dry August.

   Points towards it

   • · a dry white film on the upper leaf surface is the identification
   • · powdery mildew is unusual among fungal diseases in being worse on dry roots, not wet ones
   • · on grapes and apples the youngest shoots are colonised first

   Argues against it

   • · growth on the underside of the leaf is downy mildew, which needs wet conditions — the opposite requirement — this rules it out entirely.

   Check this next

   Rub the film between finger and thumb. Powdery mildew wipes off the upper surface and returns; downy mildew is fuzz on the underside beneath angular yellow patches. On a grape, check the fruit too — mildew on developing berries splits them.

   What to do now

   Water the roots properly and improve airflow by thinning congested growth. Dry roots are the single biggest contributor on wall-trained grapes and apples, which is the opposite of what most people assume about a fungus.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Powdery mildew — control

   Checked 2026-08-13

2. Downy mildew

   Candidate 2common on this plant

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Pea downy mildew
   • Agriculture and Horticulture Development Board — AHDB: Pulses — downy mildew

   Checked 2026-08-13

   Pale yellow patches on the upper leaf surface with a greyish or purplish furry growth directly beneath them, the patches often bounded by the leaf veins into angular blocks. It is routinely confused with powdery mildew and behaves in the opposite way: downy mildew needs wet conditions, powdery mildew thrives in dry ones.

   Points towards it

   • · a systemically infected pea carries the growth on its youngest leaves and shoot tips, which is the opposite of powdery mildew's pattern on the same crop
   • · a downy grey-brown felt on the underside rather than a dusty film on top
   • · cool wet springs are what bring it, where the powdery mildew on peas comes in a dry late summer
   • · the oospores survive in garden soil where peas have been grown before

   Argues against it

   • · peas get both mildews and the dusty one on the upper surface of older leaves in August is much the commoner
   • · warm dry weather stops downy mildew and favours the powdery one

   Check this next

   Ask which leaves are affected and when it started, because peas get both mildews and the age pattern separates them cleanly. Downy mildew takes the YOUNGEST leaves and shoot tips of a spring crop, often on plants that were stunted and distorted from the seedling stage, with a grey-brown felt on the undersides. Powdery mildew takes the OLDEST leaves of a late-sown crop in a dry August, as a dusty film on the upper surface that rubs off. Early, young, wet, underneath is downy; late, old, dry, on top is powdery.

   What to do now

   Pull out and bin badly affected plants rather than leaving them as a source, and do not compost them. Then change the ground: the resting spores persist where peas have grown, so move the next sowing well away and leave three or four years before returning. Sow thinly with wide rows so air moves through the crop, avoid overhead watering, and choose a resistant cultivar where one is offered — that and rotation are the whole of the practical control.

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Downy mildews — control
   • Agriculture and Horticulture Development Board — AHDB: Pulses — disease and rotation

   Checked 2026-08-13

Narrow it down

This page lists everything at once, which is the right shape for reading and the wrong shape for deciding. The interactive tool asks one question at a time, starting with whichever would separate these causes fastest, and stops as soon as further answers would not help.

Opens with the plant and the symptom already set. Nothing you answer is stored or sent anywhere — the answers live in the address bar and nowhere else.

What this does not cover

These are the causes GrowingHQ holds rules for on pea — not every cause there is. Where several problems look alike, the honest answer is often that they cannot be told apart by eye, and a page that named one would be guessing. If none of the above fits, the general white powdery coating on leaves page lists causes across all plants, and the Pea profile lists the problems it is prone to.