Powdery mildew is more common in barley than in wheat crops in Victoria. The powdery mildew that attacks wheat ( Blumeria graminis f. sp. tritici ) will not attack barley and vica-versa. The disease is most common in lush, early sown crops with adequate nitrogen nutrition. It is first observed during tillering, but does not normally persist beyond ear emergence. Losses in wheat in Victoria are rare.
At first, small, yellow spots appear on the leaves. Several days later a white fluffy fungus can be seen in these spots, (Figure 2.20). 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 2.20 Powdery mildew on barley. Symptoms of white fluffy fungus on leaves are similar on wheat
Each mildew infection produces masses of tiny, white spores. These are readily blown about by the wind, spreading the disease, (Figure 2.21). The fungus needs a high humidity but not rain or dew to infect the plant. Development of powdery mildew is greater at mild temperatures (15-22°C) and in lush crops. Rain suppresses development for up to five days. Hence, the disease usually occurs during drier winters in most areas.
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 most likely carries over from one season to the next on the stubble. Mildew from one cereal (eg. barley) will not infect other cereals (eg. wheat).
Figure 2.21 Disease cycle of powdery mildew on cereal. Illustration by Kylie Fowler
There are both seed and foliar fungicides available for the suppression of powdery mildew in wheat. However, in Victoria powdery mildew in wheat is normally not severe enough to warrant crop protection.
SEPTORIA LEAF BLOTCH OF WHEAT
RUSTS OF BARLEY