Pathogen 

• Urocystis agropyri

Hosts

The disease infects wheat and many grass species; the strain(s) that affect wheat are specific to that crop.

Symptoms

Affected plants are severely stunted. Excessive tillering is common and often the ears fail to emerge, remaining within the boot. Plants show 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 which are then dispersed, giving the plants the appearance of being covered in soot.

Life cycle

The teliospores released from the leaves can either be blown onto grain of healthy plants, contaminating the grain or they can drop to the soil where they are very persistent, surviving up to 4 years. When contaminated grain is sown or if healthy grain is sown into contaminated soil the teliospores germinate, producing a secondary spore type - the sporidia. These spores infect the germinating wheat seedling's coleoptile. The fungus, having penetrated the seedling then grows inside the plant, eventually producing the typical striping on the upper leaves late in the season, giving rise to a new generation of teliospores. The teliospores can survive in soil for several years so even where a break from cereals occurs, susequent wheat crops may become infected.

Importance

Flag smut of wheat occurs in some European countries and in Australia, Canada and the USA. However, it was not known in the UK until 1998 when an outbreak was confirmed in Essex. The disease in itself is not particularly damaging unless present at high levels but it can have serious consequences with regard to exporting grain or wheat products. Many countries have quarantine restrictions which prohibit the importation of wheat products from countries where the disease is established.

Cultural control

The disease is normally considered a problem on autumn sown wheat in countries with arid summers and mild winters. The disease is favoured by minimal cultivation practices which leave plant debris on the soil surface. Spring sown wheats are not affected by the disease. One to two year breaks from wheat can reduce inoculum levels and deep ploughing can help to remove to inoculum from the emerging seedlings.