Flag smut disease symptoms in wheat

Although this wheat disease is not usually damaging, it is important to identify its presence – especially if grain is destined for export markets.

The disease tends to be more problematic in areas with arid summers and mild winters. It was not known in the UK until 1998, when an outbreak was confirmed in Essex.

Autumn-sown wheat is relatively vulnerable. However, the disease is not particularly damaging, unless present at high levels. Despite this, it can have serious consequences for exported grain or wheat products. Many countries have quarantine restrictions that prohibit the import of wheat products from countries in which the disease is established.

The pathogen (Urocystis agropyri) infects wheat and many grass species. However, the strain(s) that affect wheat are specific to this crop.

When contaminated grain is sown, or if healthy grain is sown into contaminated soil, teliospores germinate.

These produce a secondary spore type (sporidia) that penetrates and infects the coleoptiles of germinating wheat.

The fungus grows inside the plant.

Affected plants are severely stunted.

Excessive tillering is common and often the ears fail to emerge, remaining within the boot.

Late in the season, typical striping symptoms show on the upper leaves – long, dark grey to black streaks on the leaf blades and leaf sheaths.

The streaks eventually erupt, giving the leaves a ragged appearance and exposing the black teliospores.

These teliospores are then dispersed, making plants look as though they are covered in soot.

The teliospores can either be blown onto grain of healthy plants, contaminating the grain, or they can drop to the soil where they survive for up to four years.

• The disease is favoured by minimal cultivation practices, which leave plant debris on the soil surface
• Deep ploughing can help to remove inoculum from the emerging seedlings
• One-to-two-year breaks from wheat can reduce inoculum levels