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Powdery Mildew

Fungus

Erysiphaceae


In a Nutshell

  • Whitish spots on leaves, stems and sometimes fruits.
  • White covering on the upper side or underside of the leaves.
  • Stunted growth.
  • Leaves shrivel and fall off.

Symptoms

The infection usually starts off as circular, powdery white spots which can affect leaves, stems and sometimes fruits. It usually covers the upper parts of the leaves but may grow on the undersides as well. The fungus hinders photosynthesis and causes the Leaves turn yellow and dry out and some leaves might twist, break or become disfigured. In the later stages, the buds and growing tips become disfigured.

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Hosts

Trigger

Fungal spores overwinter inside leaf buds and other plant debris. Wind, water, and insects transmit the spores to nearby plants. Even though it is a fungus, powdery mildew can develop rather normally in dry conditions. It survives at temperatures between 10-12°C, but optimal conditions are found at 30°C. In contrast to downy mildew, small amounts of rainfall and regular morning dew accelerate the spreading of powdery mildew.

Organic Control

Foliar sprays based on sulfur, neem oil, kaolin or ascorbic acid can prevent severe infection.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. In view of the number of crops that are susceptible to powdery mildew, it is difficult to recommend any particular chemical treatment. Fungicides based on wettable sulphur (3 g/l), hexaconazole, myclobutanil (all 2 ml/l) seem to control the growth of the fungus in some crops.

Preventive Measures

  • Use resistant or tolerant varieties.
  • Plant crops with sufficient spacing to allow for good ventilation.
  • Monitor fields regularly to assess the incidence of a disease or pest.
  • Remove infected leaves when the first spots appear.
  • Do not touch healthy plants after touching infected plants.
  • A thick layer of mulch can prevent the dispersal of spores from the soil up onto the leaves.
  • Practice crop rotation with non-susceptible crops.
  • Fertilize with a balanced nutrient supply.
  • Avoid extreme temperature changes.
  • Plow the soil thoroughly after harvest to dig plant residues deep into the soil.
  • Remove plant residues after harvest.

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