Powdery mildew in barley
Powdery mildew is one of the major diseases affecting barley. There are currently many spring barley varieties which show good varietal resistance, but the popular malting barley variety Optic is very susceptible to this disease.
With so much of the spring barley area using this variety, it has led to an increase in this disease in recent years. The disease, which affects both winter and spring varieties, produces a white fluffy fungal growth on the leaf surface.
This can cause leaves to turn yellow, leading to a loss in green leaf. High levels of disease at an early crop growth stage can kill out tillers. Many varieties show adult resistance, including Optic. This means disease levels are generally lower later in the season.
The disease is known as a biotroph which means it requires a living host to survive. A typical symptom of powdery mildew is white fluffy superficial fungal growth on the surface of leaves, stems and ears. Fungal spores which develop from these lesions are spread to other plants via the wind. The ideal infection conditions are mild and humid. Very wet conditions can limit the spread of the spores.
The disease can also overwinter in crop trash in black fungal bodies known as cleistothecia. Cereal volunteers are another method of survival. The "Green Bridge" allows powdery mildew to spread from a winter-sown crop in the autumn to the spring sown crop in the spring, to late-developing volunteers before infecting the following winter barley crop.
Diversification of varieties is one method of minimising the spread of disease from one crop to another. Many spring barley varieties have excellent resistance (mlo resistance) which has been effective in recent years.
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