Powdery Mildew on Courgettes, Squash and Peas
On this page
A dusting of white
A white, powdery coating appears on the leaves, sometimes the stems and fruit, as if dusted with talc. Once it appears, it spreads across the plant.
Which crops get it
Courgettes, marrows, cucumbers, squash, pumpkins, melons, peas, beans and brassicas are common vegetable hosts. Each mildew attacks a narrow group of plants, so the mildew on your peas will not jump to your apples.
Why dry summers bring it
Most leaf diseases need wet leaves; powdery mildew is common in warm, dry weather, helped along by humid, still air around crowded plants. A packed bed of courgettes in August is a classic setting.
What to do
- Space plants so air moves between them, and avoid heavy nitrogen feeding.
- Grow resistant varieties next year.
- Remove the worst leaves; heavy attacks weaken plants and cut yields, while light ones are mostly cosmetic.
Growing guides: courgettes (zucchini), cucumbers and peas.
Related problems: aphids, blight, yellow leaves. Or go back to all garden problems.
Powdery mildew questions
Will it kill my courgettes?
Usually not; on many plants it is unsightly rather than fatal, though heavy attacks weaken them.
Should I water the leaves?
Watering does not cause or cure it; the disease is common in warm, dry weather. Keep the roots moist and water at the base.
Regional notes
The problem is the same on both sides of the Atlantic; local advice and timing differ. Trusted local guides for this page:
- UK: RHS: Powdery mildews. Timing in your area: the UK vegetable planting calendar.
- USA: University of Wisconsin–Madison Extension: Powdery mildew; UC IPM (University of California): Powdery mildew on fruits and berries. Timing in your area: the USA vegetable planting calendar.
- Canada: your provincial agriculture department, or Canadian university gardening services. Timing in your area: the Canada vegetable planting calendar.
More problems: all garden problems.
Sources and further reading
- RHS: Powdery mildews
- University of Wisconsin–Madison Extension: Powdery mildew
- UC IPM (University of California): Powdery mildew on fruits and berries
Facts on this page are summarised in our own words from the pages above; each is supported by at least two of them, or by one plus well-established growing science (noted in our research file). Every source was opened and checked on 23 October 2026.
Keep a garden record
Most problems come back to the same beds in the same weeks. A simple record of what grew where, and when trouble started, lets you get ahead of it next year. Sketch your beds in the free Vegetable Garden Layout Planner Tool, and keep sowing dates, problems and harvests in the Global Vegetable Garden Planner (printable PDF). Every crop we cover is in the vegetable growing guides.
Last reviewed:
Fix The Cause, Then Plan The Next Crop
Troubleshooting works best when you improve the growing conditions and record what changed for the next season.
Keep going
Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.