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Disease (fungus, oomycete, bacterium, virus)

Powdery mildew

Melon leaves covered in the white powdery felt of powdery mildew.

Powdery mildew: a white, powdery felt on the upper side of the leaves, here on melon, spreading and then drying them out.

Photo: M.E. Bartolo, Bugwood.org · CC BY 3.0 · source

Role in the garden

A fungus forming a white, powdery felt on the surface of the leaves, which end up drying out.

Practical guide

Where to find them

Courgette, cucumber and melon are very susceptible to it, as is the grapevine.

Prevention

Ensure vulnerable plants have good watering and vigorous growth at the end of the season; thin the leaves so the air circulates better; avoid watering the foliage in the evening.

Early signs

A grey, powdery dust appears on some leaves and spreads rapidly to all of them. It generally shows in autumn, when the roots are dry but the air is humid.

Action / control

Pick the diseased leaves quickly to slow the progression. Throw them in the bin or burn them, as powdery mildew can survive the winter. Sprays of diluted milk (1:9) or bicarbonate of soda (5 g/L + black soap) preventively.

Sources

  • INRAE, Ephytia (protection des cultures)
  • Jardiner Autrement (SNHF, plan Écophyto)

Favourite plants / resources

Courgette (zucchini)CucumberMelonGrapesRose

Related plant entries

Courgette (zucchini)

A cucurbit (Cucurbita pepo) with separate male and female flowers on the same plant, dependent on bees and bumblebees for cross-pollination, hence the value of companion flowers nearby. Sow in pots in April or in place after the last frosts (mid-May), in rich soil well supplied with compost. Its large leaves quickly cover the ground and limit weeds; mulching and watering at the base (never on the foliage) slows the powdery mildew common in late summer. Harvesting young and regularly keeps production going.

Cucumber

A trailing cucurbit cross-pollinated by bees and bumblebees. Sow in pots in April or in place after mid-May; staking is essential beyond 1 m. Prone to leaf spot and downy mildew in late summer, water at the base only, mulch abundantly, space plants 60-80 cm apart.

Melon

A trailing cucurbit of high summer: its foliage covers the ground and limits evaporation, while its nectar-bearing flowers attract bees and bumblebees, whose pollination is essential for fruit set. Grown like squash, often on a mound of mature compost.