Powdery Mildew

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Powdery Mildew

Erysiphaceae

Fungus


In a Nutshell

  • Yellow spots on leaves.
  • White covering on the upper side or underside of the leaves.
  • Leaves shrivel and fall off.
  • Stunted growth.

Hosts:

Apple

Pear

Raspberry

Bean

Eggplant

Cherry

Apricot

Plum

Peach

Pea

Cucumber

Pumpkin

Zucchini

Tomato

Lettuce

Potato

Black & Green Gram

Pigeonpea & Red Gram

Chickpea & Gram

Cotton

Other

Maize

Citrus

Melon

Lentil

Ornamental

Symptoms

At first, yellow spots appear on the upper side of leaves. At later stage of the disease, a whitish, later greyish, floury covering spreads on leaves, stalks and fruits. The fungus extracts nutrients from the plant and the ash-like layer on the leaves hinders photosynthesis, resulting in stunted plant growth. As the disease progresses, infected parts shrivel, leaves fall off and plants might die. As opposed to Downy Mildew, Powdery Mildew can be controlled to some extent.

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.

Biological Control

For gardens, milk-water solutions seem to work as natural fungicide. Apply this solution to the leaves every second day. This household remedy works especially well with cucurbits (cucumber, zucchini, pumpkin) and berries. The types of powdery mildew differ according to the host, and this solution may not be effective for all types. If no improvement is observed, try garlic or sodium bicarbonate solutions. Commercial biological treatments are also available. Foliar sprays based on sulfur, cavonid acid, neem oil, koanin or ascorbis 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, triflumizole, 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.
  • In some cases, crop rotation with non-susceptible crops works.
  • 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.