Powdery Mildew Integrated Disease Management

POWDERY MILDEW

Common name:

Powdery Mildew

Powdery mildew on soybean plant

Source: https://extension.umn.edu/pest-management/powdery-mildew-soybean

Disease agent:

Fungi

Scientific name:

Many different strains of fungi all from the family Erisyphaceae, each specific to a different plant host.

Erysiphe spp., Sphaerotheca spp

Host range:

Wide host range, including host-specific species contained within the plant families:

Cucurbitaceae

Rosaceae

Poaceae

Solanaceae

Active season and favourable conditions:

Moderate temperatures, between 15-26C, with shady conditions favour growth of the disease. Most varieties of this disease favour warm, low humidity daytime conditions with increased humidity at night. These conditions most common during spring and summer. Spore germination is inhibited by moisture presence of leaf surfaces.

Life cycle and infection method:

Powdery mildew fungi require living tissue to grow, and once spores come into contact with leaf tissue and germination can occur. Once the spore has germinated, mycelium  can be seen growing on the surface of leaf tissue, resembling a fine white webbing. Spores are spread primarily by wind, though can also be spread by insects such as aphids, mites and fungus gnats.

Description of symptoms/damage to host plant:

Soft white spotted fungus usually in small patches resembling circles, present first on the topside or underside of leaves, then spreading to stem tissue.

Disease management options

Chemical

Sulphur, copper, potassium bicarbonate and neem oil sprays can be effective in preventing and controlling spread of the fungi.

Cultural

Spraying down leaves with water during the early morning (which allows time during the day for excess water to dry from foliage – preventing issues with other diseases from occurring as a result of the moisture) can be effective in preventing and reducing the spread of the disease if it occurs by washing away spores.

Physical

Pruning plants to increase air circulation, as well as light penetration will create conditions unfavourable for spore germination.

Removal of disease affected leaf tissue can be effective in reducing further spreading of spores.

Biological control

Ampelomyces quisqualis, Bacillus subtilis, Illeis galbula (Fungus Eating Ladybird)

Integrated Disease Management (IDM)

During spring, regular spraying down of foliage during the early morning will help to wash spores from the leaf surfaces, whilst allowing time during the day for the remaining moisture to dry, which will avoid inadvertently creating conditions that favour growth of further mildew or other diseases.

Prune plant canopy as required throughout season to increase airflow.

Fortnightly use of a neem oil or potassium bicarbonate foliar spray as an organic preventative solution. Neem oil and potassium bicarbonate can also be effective for treating outbreaks of powdery mildew as they occur.

Prune away any and discard of any diseased tissue to control further spread.

Potassium bicarbonate based fungicides as well as neem oil, lime sulphur, and copper are all effective at controlling powdery mildew as well as being environmentally friendly and do no harm to beneficial insects when used at correct concentrations.