Downy Mildew
Causal Agent
Sclerophthora macrospora
What is Downy Mildew?
Downy mildew is a fungal disease that affects many plants and appears as yellow to white patches on the upper surfaces of older leaves. On the undersides, these areas are covered with white to grayish, cotton-like fungi. These “downy” masses are most often noticed after rain or heavy dew and disappear soon after sunny weather resumes.
Downy mildew occurs mostly in cool, moist weather, usually in early spring or late autumn. This disease overwinters on plant debris and in the soil.
What are the symptoms of Downy Mildew?
Symptoms of downy mildew include:
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Early symptoms are slightly stunted growth and slightly thickened or broadened leaf blades without any discolouration.
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A white downy growth may occur on leaf surfaces during cool, wet periods.
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When the disease is severe, small yellow circular patches 1 to 10cm in diameter appear on the turf.
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Patches contain a dense cluster of excessively tillered yellow shoots with shortened roots, which are easily pulled from the turf.
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Infected new seedling turf form individual clusters of dense shoots that are yellow in colour.
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As the disease progresses leaves may eventually turn crisp and brown and fall off even though the plant has ample water.
Downy Mildew INFO SHEETWhat causes Downy Mildew?
Downy mildew is caused by the fungi Sclerophthora macrospora. These fungal spores can be carried by insects, wind, rain or garden tools.
What turfgrasses are particularly susceptible to Downy Mildew?
All cool-season turfgrass species are susceptible to Downy Mildew.
When does Downy Mildew Occur?
In general, conditions that favour downy mildew include:
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Wet conditions are required
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The yellow tufting symptom occurs more commonly in temperate climates, with the downy growth occurring only in warmer weather.
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Typically occurs in wet, poorly drained low areas.
What can I do to manage or control Downy Mildew?
Management practices that can help manage or control downy mildew include:
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Improving drainage of the turf.
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Increasing air circulation.
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Using proper surface contours to minimise water movement and accumulation on the turf’s surface.
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Avoiding high or excessive levels of nitrogen that result in lush growth.
