Powdery Mildew

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Powdery Mildew

Erysiphaceae

Fungus


In a Nutshell

  • Floury covering on leaves which can be wiped off.

Hosts

Additional

Apple

Apricot

Bean

Cabbage

Canola

Capsicum & Chili

Carrots

Cherry

Chickpea, Gram

Citrus

Cotton

Cucumber

Eggplant

Lentil

Lettuce

Mung bean

Ornamental

Pea

Peach

Pear

Plum

Potato

Pumpkin

Raspberry

Red gram, Pigeonpea

Tomato

Zucchini

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.

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, hexaconazole, triflumizole, myclobutanil, 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.,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 works.,Fertilize with a balanced nutrient supply.,Avoid extreme temperature changes.,Plow in or remove plant residues after harvest.