POWDERY MILDEW OF BARLEY

Powdery mildew is a common disease of barley crops and is caused by the fungus Blumeria graminis f. sp hordei. The disease is most common in early sown crops with good canopy cover and good nitrogen nutrition. Symptoms are usually first observed during tillering but the disease does not normally persist beyond ear emergence. Losses are typically minimal in Victoria, but can be as much as 25 percent in heavily-infected crops, which has been observed in South and Western Australia.

What to Look For

At first, small, yellow spots appear on the leaves. Several days later a white fluffy fungus can be seen in these spots, (Figure 2.34). The fungus can infect all above-ground parts of the plant including the head. It causes yellowing and early death of leaves. Later in the season the fungus produces small black specks. These are commonly found in old infections near the base of the plant.

Figure 2.34 Powdery mildew on barley

Disease Cycle

Powdery mildew infection produces masses of tiny, white spores which are spread when blown by the wind. Infection occurs when there is high humidity from dew and temperatures between 15-25 °C and is suppressed by rain resulting in powdery mildew being more severe during drier conditions. Mildew symptoms usually appear five to seven days after infection. The fungus can multiply quickly and crops can become heavily diseased within four to five weeks of the first signs of the disease. The disease carries over from one season to the next on volunteers and grasses. Mildews are host specific and, therefore, mildew from barley will not infect wheat, (Figure 2.35).

Figure 2.35 Disease cycle of powdery mildew on cereals. Illustration by Kylie Fowler

Powdery Mildew of Barley Management

Cultural

No stubble treatments or crop rotations will effectively control powdery mildew because spores can be readily blown onto a healthy crop from diseased crops in the district. However, removing the volunteers by grazing and by herbicides will assist in reducing inoculum loads.

Cultivars

Barley varieties vary in their susceptibility to powdery mildew so consult a current Victorian Cereal Disease Guide (AG 1160) to determine risk.

Powdery Mildew of Barley Management

Cultural

No stubble treatments or crop rotations will effectively control powdery mildew because spores can be readily blown onto a healthy crop from diseased crops in the district. However, removing the volunteers by grazing and by herbicides will assist in reducing inoculum loads.

Cultivars

Barley varieties vary in their susceptibility to powdery mildew so consult a current Victorian Cereal Disease Guide (AG 1160) to determine risk.

Chemicals

Some seed treatment fungicides will suppress the powdery mildew for 6-8 weeks following sowing. This form of control is recommended in barley crops that are sown early and in areas prone to powdery mildew. Some foliar fungicides effectively suppress development of powdery mildew and are best applied before the disease has infected 5 percent of leaf area of the lowest green leaves. Reduced effectiveness of some triazole fungicides has been observed in Western Australia during recent seasons. Crops in eastern Australia should be monitored for signs of reduced sensitivity by powdery mildew to fungicides and samples submitted to the DEDJTR for testing.

Further Information

More detailed information can be obtained from the DEDJTR AgNotes Series www.vic.gov.au/graindiseases

Victorian Cereal Diseases Guide (AG 1160) www.vic.gov.au/cerealdiseaseguide

Victorian Winter Crop Summary www.vic.gov.au/victorianwintercropsummary

Wallwork H (2015) Cereal Seed Treatments (SARDI) www.pir.sa.gov.au, http://www.pir.sa.gov.au/ data/ assets/pdf_file/0005/237920/cerealseedtreat2015_web.pdf

Wallwork H (2000) Cereal Leaf and Stem Diseases (SARDI) www.grdc.com.au/bookshop

NET BLOTCH OF BARLEY

Soil-borne Diseases of Cereals