Downy Mildew of Wheat

Sclerophthora macrospora

Names:

Crazy Top.
Yellow Tuff of Turf.
Downy Mildew of Turf.

Description:

Yellow leaves, stunting, excessive tillering and occasionally early death of young plants. Older plants often have twisted, leathery and thickened leaves. Heads on surviving plants may be distorted, twisted and thickened ("Crazy Top") with little grain. Usually associated with plants growing in or very near standing water.
In turf grasses the there is initial stunting that is followed by circular yellow patches that are 1-10 cm in diameter. The plants in these patches have stunted roots and may be easily pulled up. White, downy mycelia may cover the leaves during cool wet weather. It is often difficult to see in mown turf.
Symptoms may vary depending on the species of grass.

Species Affected:

Wheat including Durum Wheat, Barley, Cereal Rye, Maize, Oats, Sorghum, Triticale and many grasses including most cool season turf grasses.

Biology:

Usually occurs in waterlogged conditions.
The fungus will survive for months in well drained soils.
Prefers humid rainy weather with day temperatures of 30-350C and night temperatures above 200C. It requires a relative humidity of more than 90% for 10 hours with temperatures above 200C.

Life Cycle:

The fungus survives in the soil and after irrigation or waterlogging spores are released that swim to infect plants in water.
It usually appears in early to late spring or autumn

Origin and History:

Distribution:

Often more common on the edges of paddocks where grasses are a source of infection and in waterlogged areas.
Found mainly in summer irrigation areas.

Significance:

Not common.
Yield reductions in affected areas can be high but it is rare to have large areas affected.

Management and Control:

Reduce waterlogging and inundation.
Control grasses that may be a source of infection.
Avoid nitrogen applications that produce very lush growth.
Improve air circulation.

Related and Similar Species:

References:

1293

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.